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1878
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1 /*
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1972
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2 * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved.
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1878
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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1972
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25 #include "precompiled.hpp"
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26 #include "classfile/vmSymbols.hpp"
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27 #include "memory/resourceArea.hpp"
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28 #include "oops/markOop.hpp"
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29 #include "oops/oop.inline.hpp"
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30 #include "runtime/handles.inline.hpp"
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31 #include "runtime/interfaceSupport.hpp"
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32 #include "runtime/mutexLocker.hpp"
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33 #include "runtime/objectMonitor.hpp"
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34 #include "runtime/objectMonitor.inline.hpp"
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35 #include "runtime/osThread.hpp"
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36 #include "runtime/stubRoutines.hpp"
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37 #include "runtime/thread.hpp"
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38 #include "services/threadService.hpp"
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39 #include "utilities/dtrace.hpp"
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40 #include "utilities/preserveException.hpp"
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41 #ifdef TARGET_OS_FAMILY_linux
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42 # include "os_linux.inline.hpp"
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43 # include "thread_linux.inline.hpp"
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44 #endif
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45 #ifdef TARGET_OS_FAMILY_solaris
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46 # include "os_solaris.inline.hpp"
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47 # include "thread_solaris.inline.hpp"
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48 #endif
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49 #ifdef TARGET_OS_FAMILY_windows
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50 # include "os_windows.inline.hpp"
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51 # include "thread_windows.inline.hpp"
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52 #endif
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1878
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53
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54 #if defined(__GNUC__) && !defined(IA64)
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55 // Need to inhibit inlining for older versions of GCC to avoid build-time failures
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56 #define ATTR __attribute__((noinline))
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57 #else
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58 #define ATTR
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59 #endif
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60
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61
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62 #ifdef DTRACE_ENABLED
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63
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64 // Only bother with this argument setup if dtrace is available
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65 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
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66
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67 HS_DTRACE_PROBE_DECL4(hotspot, monitor__notify,
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68 jlong, uintptr_t, char*, int);
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69 HS_DTRACE_PROBE_DECL4(hotspot, monitor__notifyAll,
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70 jlong, uintptr_t, char*, int);
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71 HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__enter,
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72 jlong, uintptr_t, char*, int);
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73 HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__entered,
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74 jlong, uintptr_t, char*, int);
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75 HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__exit,
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76 jlong, uintptr_t, char*, int);
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77
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78 #define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread) \
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79 char* bytes = NULL; \
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80 int len = 0; \
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81 jlong jtid = SharedRuntime::get_java_tid(thread); \
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82 symbolOop klassname = ((oop)(klassOop))->klass()->klass_part()->name(); \
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83 if (klassname != NULL) { \
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84 bytes = (char*)klassname->bytes(); \
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85 len = klassname->utf8_length(); \
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86 }
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87
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88 #define DTRACE_MONITOR_WAIT_PROBE(monitor, klassOop, thread, millis) \
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89 { \
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90 if (DTraceMonitorProbes) { \
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91 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \
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92 HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \
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93 (monitor), bytes, len, (millis)); \
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94 } \
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95 }
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96
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97 #define DTRACE_MONITOR_PROBE(probe, monitor, klassOop, thread) \
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98 { \
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99 if (DTraceMonitorProbes) { \
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100 DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \
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101 HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \
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102 (uintptr_t)(monitor), bytes, len); \
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103 } \
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104 }
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105
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106 #else // ndef DTRACE_ENABLED
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107
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108 #define DTRACE_MONITOR_WAIT_PROBE(klassOop, thread, millis, mon) {;}
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109 #define DTRACE_MONITOR_PROBE(probe, klassOop, thread, mon) {;}
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110
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111 #endif // ndef DTRACE_ENABLED
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112
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113 // Tunables ...
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114 // The knob* variables are effectively final. Once set they should
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115 // never be modified hence. Consider using __read_mostly with GCC.
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116
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117 int ObjectMonitor::Knob_Verbose = 0 ;
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118 int ObjectMonitor::Knob_SpinLimit = 5000 ; // derived by an external tool -
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119 static int Knob_LogSpins = 0 ; // enable jvmstat tally for spins
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120 static int Knob_HandOff = 0 ;
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121 static int Knob_ReportSettings = 0 ;
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122
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123 static int Knob_SpinBase = 0 ; // Floor AKA SpinMin
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124 static int Knob_SpinBackOff = 0 ; // spin-loop backoff
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125 static int Knob_CASPenalty = -1 ; // Penalty for failed CAS
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126 static int Knob_OXPenalty = -1 ; // Penalty for observed _owner change
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127 static int Knob_SpinSetSucc = 1 ; // spinners set the _succ field
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128 static int Knob_SpinEarly = 1 ;
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129 static int Knob_SuccEnabled = 1 ; // futile wake throttling
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130 static int Knob_SuccRestrict = 0 ; // Limit successors + spinners to at-most-one
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131 static int Knob_MaxSpinners = -1 ; // Should be a function of # CPUs
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132 static int Knob_Bonus = 100 ; // spin success bonus
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133 static int Knob_BonusB = 100 ; // spin success bonus
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134 static int Knob_Penalty = 200 ; // spin failure penalty
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135 static int Knob_Poverty = 1000 ;
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136 static int Knob_SpinAfterFutile = 1 ; // Spin after returning from park()
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137 static int Knob_FixedSpin = 0 ;
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138 static int Knob_OState = 3 ; // Spinner checks thread state of _owner
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139 static int Knob_UsePause = 1 ;
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140 static int Knob_ExitPolicy = 0 ;
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141 static int Knob_PreSpin = 10 ; // 20-100 likely better
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142 static int Knob_ResetEvent = 0 ;
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143 static int BackOffMask = 0 ;
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144
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145 static int Knob_FastHSSEC = 0 ;
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146 static int Knob_MoveNotifyee = 2 ; // notify() - disposition of notifyee
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147 static int Knob_QMode = 0 ; // EntryList-cxq policy - queue discipline
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148 static volatile int InitDone = 0 ;
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149
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150 #define TrySpin TrySpin_VaryDuration
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151
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152 // -----------------------------------------------------------------------------
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153 // Theory of operations -- Monitors lists, thread residency, etc:
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154 //
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155 // * A thread acquires ownership of a monitor by successfully
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156 // CAS()ing the _owner field from null to non-null.
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157 //
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158 // * Invariant: A thread appears on at most one monitor list --
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159 // cxq, EntryList or WaitSet -- at any one time.
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160 //
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161 // * Contending threads "push" themselves onto the cxq with CAS
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162 // and then spin/park.
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163 //
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164 // * After a contending thread eventually acquires the lock it must
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165 // dequeue itself from either the EntryList or the cxq.
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166 //
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167 // * The exiting thread identifies and unparks an "heir presumptive"
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168 // tentative successor thread on the EntryList. Critically, the
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169 // exiting thread doesn't unlink the successor thread from the EntryList.
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170 // After having been unparked, the wakee will recontend for ownership of
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171 // the monitor. The successor (wakee) will either acquire the lock or
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172 // re-park itself.
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173 //
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174 // Succession is provided for by a policy of competitive handoff.
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175 // The exiting thread does _not_ grant or pass ownership to the
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176 // successor thread. (This is also referred to as "handoff" succession").
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177 // Instead the exiting thread releases ownership and possibly wakes
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178 // a successor, so the successor can (re)compete for ownership of the lock.
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179 // If the EntryList is empty but the cxq is populated the exiting
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180 // thread will drain the cxq into the EntryList. It does so by
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181 // by detaching the cxq (installing null with CAS) and folding
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182 // the threads from the cxq into the EntryList. The EntryList is
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183 // doubly linked, while the cxq is singly linked because of the
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184 // CAS-based "push" used to enqueue recently arrived threads (RATs).
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185 //
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186 // * Concurrency invariants:
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187 //
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188 // -- only the monitor owner may access or mutate the EntryList.
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189 // The mutex property of the monitor itself protects the EntryList
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190 // from concurrent interference.
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191 // -- Only the monitor owner may detach the cxq.
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192 //
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193 // * The monitor entry list operations avoid locks, but strictly speaking
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194 // they're not lock-free. Enter is lock-free, exit is not.
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195 // See http://j2se.east/~dice/PERSIST/040825-LockFreeQueues.html
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196 //
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197 // * The cxq can have multiple concurrent "pushers" but only one concurrent
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198 // detaching thread. This mechanism is immune from the ABA corruption.
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199 // More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
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200 //
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201 // * Taken together, the cxq and the EntryList constitute or form a
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202 // single logical queue of threads stalled trying to acquire the lock.
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203 // We use two distinct lists to improve the odds of a constant-time
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204 // dequeue operation after acquisition (in the ::enter() epilog) and
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205 // to reduce heat on the list ends. (c.f. Michael Scott's "2Q" algorithm).
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206 // A key desideratum is to minimize queue & monitor metadata manipulation
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207 // that occurs while holding the monitor lock -- that is, we want to
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208 // minimize monitor lock holds times. Note that even a small amount of
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209 // fixed spinning will greatly reduce the # of enqueue-dequeue operations
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210 // on EntryList|cxq. That is, spinning relieves contention on the "inner"
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211 // locks and monitor metadata.
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212 //
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213 // Cxq points to the the set of Recently Arrived Threads attempting entry.
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214 // Because we push threads onto _cxq with CAS, the RATs must take the form of
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215 // a singly-linked LIFO. We drain _cxq into EntryList at unlock-time when
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216 // the unlocking thread notices that EntryList is null but _cxq is != null.
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217 //
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218 // The EntryList is ordered by the prevailing queue discipline and
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219 // can be organized in any convenient fashion, such as a doubly-linked list or
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220 // a circular doubly-linked list. Critically, we want insert and delete operations
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221 // to operate in constant-time. If we need a priority queue then something akin
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222 // to Solaris' sleepq would work nicely. Viz.,
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223 // http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
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224 // Queue discipline is enforced at ::exit() time, when the unlocking thread
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225 // drains the cxq into the EntryList, and orders or reorders the threads on the
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226 // EntryList accordingly.
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227 //
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228 // Barring "lock barging", this mechanism provides fair cyclic ordering,
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229 // somewhat similar to an elevator-scan.
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230 //
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231 // * The monitor synchronization subsystem avoids the use of native
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232 // synchronization primitives except for the narrow platform-specific
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233 // park-unpark abstraction. See the comments in os_solaris.cpp regarding
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234 // the semantics of park-unpark. Put another way, this monitor implementation
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235 // depends only on atomic operations and park-unpark. The monitor subsystem
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236 // manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
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237 // underlying OS manages the READY<->RUN transitions.
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238 //
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239 // * Waiting threads reside on the WaitSet list -- wait() puts
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240 // the caller onto the WaitSet.
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241 //
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242 // * notify() or notifyAll() simply transfers threads from the WaitSet to
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243 // either the EntryList or cxq. Subsequent exit() operations will
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244 // unpark the notifyee. Unparking a notifee in notify() is inefficient -
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245 // it's likely the notifyee would simply impale itself on the lock held
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246 // by the notifier.
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247 //
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248 // * An interesting alternative is to encode cxq as (List,LockByte) where
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249 // the LockByte is 0 iff the monitor is owned. _owner is simply an auxiliary
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250 // variable, like _recursions, in the scheme. The threads or Events that form
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251 // the list would have to be aligned in 256-byte addresses. A thread would
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252 // try to acquire the lock or enqueue itself with CAS, but exiting threads
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253 // could use a 1-0 protocol and simply STB to set the LockByte to 0.
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254 // Note that is is *not* word-tearing, but it does presume that full-word
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255 // CAS operations are coherent with intermix with STB operations. That's true
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256 // on most common processors.
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257 //
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258 // * See also http://blogs.sun.com/dave
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259
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260
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261 // -----------------------------------------------------------------------------
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262 // Enter support
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263
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264 bool ObjectMonitor::try_enter(Thread* THREAD) {
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265 if (THREAD != _owner) {
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266 if (THREAD->is_lock_owned ((address)_owner)) {
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267 assert(_recursions == 0, "internal state error");
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268 _owner = THREAD ;
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269 _recursions = 1 ;
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270 OwnerIsThread = 1 ;
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271 return true;
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272 }
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273 if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
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274 return false;
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275 }
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276 return true;
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277 } else {
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278 _recursions++;
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279 return true;
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280 }
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281 }
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282
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283 void ATTR ObjectMonitor::enter(TRAPS) {
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284 // The following code is ordered to check the most common cases first
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285 // and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
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286 Thread * const Self = THREAD ;
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287 void * cur ;
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288
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289 cur = Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
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290 if (cur == NULL) {
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291 // Either ASSERT _recursions == 0 or explicitly set _recursions = 0.
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292 assert (_recursions == 0 , "invariant") ;
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293 assert (_owner == Self, "invariant") ;
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294 // CONSIDER: set or assert OwnerIsThread == 1
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295 return ;
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296 }
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297
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298 if (cur == Self) {
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299 // TODO-FIXME: check for integer overflow! BUGID 6557169.
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300 _recursions ++ ;
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301 return ;
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302 }
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303
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304 if (Self->is_lock_owned ((address)cur)) {
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305 assert (_recursions == 0, "internal state error");
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306 _recursions = 1 ;
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307 // Commute owner from a thread-specific on-stack BasicLockObject address to
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308 // a full-fledged "Thread *".
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309 _owner = Self ;
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310 OwnerIsThread = 1 ;
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311 return ;
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312 }
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313
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314 // We've encountered genuine contention.
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315 assert (Self->_Stalled == 0, "invariant") ;
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316 Self->_Stalled = intptr_t(this) ;
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317
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318 // Try one round of spinning *before* enqueueing Self
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319 // and before going through the awkward and expensive state
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320 // transitions. The following spin is strictly optional ...
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321 // Note that if we acquire the monitor from an initial spin
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322 // we forgo posting JVMTI events and firing DTRACE probes.
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323 if (Knob_SpinEarly && TrySpin (Self) > 0) {
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324 assert (_owner == Self , "invariant") ;
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325 assert (_recursions == 0 , "invariant") ;
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326 assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
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327 Self->_Stalled = 0 ;
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328 return ;
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329 }
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330
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331 assert (_owner != Self , "invariant") ;
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332 assert (_succ != Self , "invariant") ;
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333 assert (Self->is_Java_thread() , "invariant") ;
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334 JavaThread * jt = (JavaThread *) Self ;
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335 assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
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336 assert (jt->thread_state() != _thread_blocked , "invariant") ;
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337 assert (this->object() != NULL , "invariant") ;
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338 assert (_count >= 0, "invariant") ;
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339
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340 // Prevent deflation at STW-time. See deflate_idle_monitors() and is_busy().
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341 // Ensure the object-monitor relationship remains stable while there's contention.
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342 Atomic::inc_ptr(&_count);
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343
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344 { // Change java thread status to indicate blocked on monitor enter.
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345 JavaThreadBlockedOnMonitorEnterState jtbmes(jt, this);
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346
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347 DTRACE_MONITOR_PROBE(contended__enter, this, object(), jt);
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348 if (JvmtiExport::should_post_monitor_contended_enter()) {
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349 JvmtiExport::post_monitor_contended_enter(jt, this);
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350 }
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351
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352 OSThreadContendState osts(Self->osthread());
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353 ThreadBlockInVM tbivm(jt);
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354
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355 Self->set_current_pending_monitor(this);
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356
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357 // TODO-FIXME: change the following for(;;) loop to straight-line code.
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358 for (;;) {
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359 jt->set_suspend_equivalent();
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360 // cleared by handle_special_suspend_equivalent_condition()
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361 // or java_suspend_self()
|
|
|
362
|
|
|
363 EnterI (THREAD) ;
|
|
|
364
|
|
|
365 if (!ExitSuspendEquivalent(jt)) break ;
|
|
|
366
|
|
|
367 //
|
|
|
368 // We have acquired the contended monitor, but while we were
|
|
|
369 // waiting another thread suspended us. We don't want to enter
|
|
|
370 // the monitor while suspended because that would surprise the
|
|
|
371 // thread that suspended us.
|
|
|
372 //
|
|
|
373 _recursions = 0 ;
|
|
|
374 _succ = NULL ;
|
|
|
375 exit (Self) ;
|
|
|
376
|
|
|
377 jt->java_suspend_self();
|
|
|
378 }
|
|
|
379 Self->set_current_pending_monitor(NULL);
|
|
|
380 }
|
|
|
381
|
|
|
382 Atomic::dec_ptr(&_count);
|
|
|
383 assert (_count >= 0, "invariant") ;
|
|
|
384 Self->_Stalled = 0 ;
|
|
|
385
|
|
|
386 // Must either set _recursions = 0 or ASSERT _recursions == 0.
|
|
|
387 assert (_recursions == 0 , "invariant") ;
|
|
|
388 assert (_owner == Self , "invariant") ;
|
|
|
389 assert (_succ != Self , "invariant") ;
|
|
|
390 assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
|
|
|
391
|
|
|
392 // The thread -- now the owner -- is back in vm mode.
|
|
|
393 // Report the glorious news via TI,DTrace and jvmstat.
|
|
|
394 // The probe effect is non-trivial. All the reportage occurs
|
|
|
395 // while we hold the monitor, increasing the length of the critical
|
|
|
396 // section. Amdahl's parallel speedup law comes vividly into play.
|
|
|
397 //
|
|
|
398 // Another option might be to aggregate the events (thread local or
|
|
|
399 // per-monitor aggregation) and defer reporting until a more opportune
|
|
|
400 // time -- such as next time some thread encounters contention but has
|
|
|
401 // yet to acquire the lock. While spinning that thread could
|
|
|
402 // spinning we could increment JVMStat counters, etc.
|
|
|
403
|
|
|
404 DTRACE_MONITOR_PROBE(contended__entered, this, object(), jt);
|
|
|
405 if (JvmtiExport::should_post_monitor_contended_entered()) {
|
|
|
406 JvmtiExport::post_monitor_contended_entered(jt, this);
|
|
|
407 }
|
|
|
408 if (ObjectMonitor::_sync_ContendedLockAttempts != NULL) {
|
|
|
409 ObjectMonitor::_sync_ContendedLockAttempts->inc() ;
|
|
|
410 }
|
|
|
411 }
|
|
|
412
|
|
|
413
|
|
|
414 // Caveat: TryLock() is not necessarily serializing if it returns failure.
|
|
|
415 // Callers must compensate as needed.
|
|
|
416
|
|
|
417 int ObjectMonitor::TryLock (Thread * Self) {
|
|
|
418 for (;;) {
|
|
|
419 void * own = _owner ;
|
|
|
420 if (own != NULL) return 0 ;
|
|
|
421 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
|
|
|
422 // Either guarantee _recursions == 0 or set _recursions = 0.
|
|
|
423 assert (_recursions == 0, "invariant") ;
|
|
|
424 assert (_owner == Self, "invariant") ;
|
|
|
425 // CONSIDER: set or assert that OwnerIsThread == 1
|
|
|
426 return 1 ;
|
|
|
427 }
|
|
|
428 // The lock had been free momentarily, but we lost the race to the lock.
|
|
|
429 // Interference -- the CAS failed.
|
|
|
430 // We can either return -1 or retry.
|
|
|
431 // Retry doesn't make as much sense because the lock was just acquired.
|
|
|
432 if (true) return -1 ;
|
|
|
433 }
|
|
|
434 }
|
|
|
435
|
|
|
436 void ATTR ObjectMonitor::EnterI (TRAPS) {
|
|
|
437 Thread * Self = THREAD ;
|
|
|
438 assert (Self->is_Java_thread(), "invariant") ;
|
|
|
439 assert (((JavaThread *) Self)->thread_state() == _thread_blocked , "invariant") ;
|
|
|
440
|
|
|
441 // Try the lock - TATAS
|
|
|
442 if (TryLock (Self) > 0) {
|
|
|
443 assert (_succ != Self , "invariant") ;
|
|
|
444 assert (_owner == Self , "invariant") ;
|
|
|
445 assert (_Responsible != Self , "invariant") ;
|
|
|
446 return ;
|
|
|
447 }
|
|
|
448
|
|
|
449 DeferredInitialize () ;
|
|
|
450
|
|
|
451 // We try one round of spinning *before* enqueueing Self.
|
|
|
452 //
|
|
|
453 // If the _owner is ready but OFFPROC we could use a YieldTo()
|
|
|
454 // operation to donate the remainder of this thread's quantum
|
|
|
455 // to the owner. This has subtle but beneficial affinity
|
|
|
456 // effects.
|
|
|
457
|
|
|
458 if (TrySpin (Self) > 0) {
|
|
|
459 assert (_owner == Self , "invariant") ;
|
|
|
460 assert (_succ != Self , "invariant") ;
|
|
|
461 assert (_Responsible != Self , "invariant") ;
|
|
|
462 return ;
|
|
|
463 }
|
|
|
464
|
|
|
465 // The Spin failed -- Enqueue and park the thread ...
|
|
|
466 assert (_succ != Self , "invariant") ;
|
|
|
467 assert (_owner != Self , "invariant") ;
|
|
|
468 assert (_Responsible != Self , "invariant") ;
|
|
|
469
|
|
|
470 // Enqueue "Self" on ObjectMonitor's _cxq.
|
|
|
471 //
|
|
|
472 // Node acts as a proxy for Self.
|
|
|
473 // As an aside, if were to ever rewrite the synchronization code mostly
|
|
|
474 // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
|
|
|
475 // Java objects. This would avoid awkward lifecycle and liveness issues,
|
|
|
476 // as well as eliminate a subset of ABA issues.
|
|
|
477 // TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
|
|
|
478 //
|
|
|
479
|
|
|
480 ObjectWaiter node(Self) ;
|
|
|
481 Self->_ParkEvent->reset() ;
|
|
|
482 node._prev = (ObjectWaiter *) 0xBAD ;
|
|
|
483 node.TState = ObjectWaiter::TS_CXQ ;
|
|
|
484
|
|
|
485 // Push "Self" onto the front of the _cxq.
|
|
|
486 // Once on cxq/EntryList, Self stays on-queue until it acquires the lock.
|
|
|
487 // Note that spinning tends to reduce the rate at which threads
|
|
|
488 // enqueue and dequeue on EntryList|cxq.
|
|
|
489 ObjectWaiter * nxt ;
|
|
|
490 for (;;) {
|
|
|
491 node._next = nxt = _cxq ;
|
|
|
492 if (Atomic::cmpxchg_ptr (&node, &_cxq, nxt) == nxt) break ;
|
|
|
493
|
|
|
494 // Interference - the CAS failed because _cxq changed. Just retry.
|
|
|
495 // As an optional optimization we retry the lock.
|
|
|
496 if (TryLock (Self) > 0) {
|
|
|
497 assert (_succ != Self , "invariant") ;
|
|
|
498 assert (_owner == Self , "invariant") ;
|
|
|
499 assert (_Responsible != Self , "invariant") ;
|
|
|
500 return ;
|
|
|
501 }
|
|
|
502 }
|
|
|
503
|
|
|
504 // Check for cxq|EntryList edge transition to non-null. This indicates
|
|
|
505 // the onset of contention. While contention persists exiting threads
|
|
|
506 // will use a ST:MEMBAR:LD 1-1 exit protocol. When contention abates exit
|
|
|
507 // operations revert to the faster 1-0 mode. This enter operation may interleave
|
|
|
508 // (race) a concurrent 1-0 exit operation, resulting in stranding, so we
|
|
|
509 // arrange for one of the contending thread to use a timed park() operations
|
|
|
510 // to detect and recover from the race. (Stranding is form of progress failure
|
|
|
511 // where the monitor is unlocked but all the contending threads remain parked).
|
|
|
512 // That is, at least one of the contended threads will periodically poll _owner.
|
|
|
513 // One of the contending threads will become the designated "Responsible" thread.
|
|
|
514 // The Responsible thread uses a timed park instead of a normal indefinite park
|
|
|
515 // operation -- it periodically wakes and checks for and recovers from potential
|
|
|
516 // strandings admitted by 1-0 exit operations. We need at most one Responsible
|
|
|
517 // thread per-monitor at any given moment. Only threads on cxq|EntryList may
|
|
|
518 // be responsible for a monitor.
|
|
|
519 //
|
|
|
520 // Currently, one of the contended threads takes on the added role of "Responsible".
|
|
|
521 // A viable alternative would be to use a dedicated "stranding checker" thread
|
|
|
522 // that periodically iterated over all the threads (or active monitors) and unparked
|
|
|
523 // successors where there was risk of stranding. This would help eliminate the
|
|
|
524 // timer scalability issues we see on some platforms as we'd only have one thread
|
|
|
525 // -- the checker -- parked on a timer.
|
|
|
526
|
|
|
527 if ((SyncFlags & 16) == 0 && nxt == NULL && _EntryList == NULL) {
|
|
|
528 // Try to assume the role of responsible thread for the monitor.
|
|
|
529 // CONSIDER: ST vs CAS vs { if (Responsible==null) Responsible=Self }
|
|
|
530 Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
|
|
|
531 }
|
|
|
532
|
|
|
533 // The lock have been released while this thread was occupied queueing
|
|
|
534 // itself onto _cxq. To close the race and avoid "stranding" and
|
|
|
535 // progress-liveness failure we must resample-retry _owner before parking.
|
|
|
536 // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
|
|
|
537 // In this case the ST-MEMBAR is accomplished with CAS().
|
|
|
538 //
|
|
|
539 // TODO: Defer all thread state transitions until park-time.
|
|
|
540 // Since state transitions are heavy and inefficient we'd like
|
|
|
541 // to defer the state transitions until absolutely necessary,
|
|
|
542 // and in doing so avoid some transitions ...
|
|
|
543
|
|
|
544 TEVENT (Inflated enter - Contention) ;
|
|
|
545 int nWakeups = 0 ;
|
|
|
546 int RecheckInterval = 1 ;
|
|
|
547
|
|
|
548 for (;;) {
|
|
|
549
|
|
|
550 if (TryLock (Self) > 0) break ;
|
|
|
551 assert (_owner != Self, "invariant") ;
|
|
|
552
|
|
|
553 if ((SyncFlags & 2) && _Responsible == NULL) {
|
|
|
554 Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
|
|
|
555 }
|
|
|
556
|
|
|
557 // park self
|
|
|
558 if (_Responsible == Self || (SyncFlags & 1)) {
|
|
|
559 TEVENT (Inflated enter - park TIMED) ;
|
|
|
560 Self->_ParkEvent->park ((jlong) RecheckInterval) ;
|
|
|
561 // Increase the RecheckInterval, but clamp the value.
|
|
|
562 RecheckInterval *= 8 ;
|
|
|
563 if (RecheckInterval > 1000) RecheckInterval = 1000 ;
|
|
|
564 } else {
|
|
|
565 TEVENT (Inflated enter - park UNTIMED) ;
|
|
|
566 Self->_ParkEvent->park() ;
|
|
|
567 }
|
|
|
568
|
|
|
569 if (TryLock(Self) > 0) break ;
|
|
|
570
|
|
|
571 // The lock is still contested.
|
|
|
572 // Keep a tally of the # of futile wakeups.
|
|
|
573 // Note that the counter is not protected by a lock or updated by atomics.
|
|
|
574 // That is by design - we trade "lossy" counters which are exposed to
|
|
|
575 // races during updates for a lower probe effect.
|
|
|
576 TEVENT (Inflated enter - Futile wakeup) ;
|
|
|
577 if (ObjectMonitor::_sync_FutileWakeups != NULL) {
|
|
|
578 ObjectMonitor::_sync_FutileWakeups->inc() ;
|
|
|
579 }
|
|
|
580 ++ nWakeups ;
|
|
|
581
|
|
|
582 // Assuming this is not a spurious wakeup we'll normally find _succ == Self.
|
|
|
583 // We can defer clearing _succ until after the spin completes
|
|
|
584 // TrySpin() must tolerate being called with _succ == Self.
|
|
|
585 // Try yet another round of adaptive spinning.
|
|
|
586 if ((Knob_SpinAfterFutile & 1) && TrySpin (Self) > 0) break ;
|
|
|
587
|
|
|
588 // We can find that we were unpark()ed and redesignated _succ while
|
|
|
589 // we were spinning. That's harmless. If we iterate and call park(),
|
|
|
590 // park() will consume the event and return immediately and we'll
|
|
|
591 // just spin again. This pattern can repeat, leaving _succ to simply
|
|
|
592 // spin on a CPU. Enable Knob_ResetEvent to clear pending unparks().
|
|
|
593 // Alternately, we can sample fired() here, and if set, forgo spinning
|
|
|
594 // in the next iteration.
|
|
|
595
|
|
|
596 if ((Knob_ResetEvent & 1) && Self->_ParkEvent->fired()) {
|
|
|
597 Self->_ParkEvent->reset() ;
|
|
|
598 OrderAccess::fence() ;
|
|
|
599 }
|
|
|
600 if (_succ == Self) _succ = NULL ;
|
|
|
601
|
|
|
602 // Invariant: after clearing _succ a thread *must* retry _owner before parking.
|
|
|
603 OrderAccess::fence() ;
|
|
|
604 }
|
|
|
605
|
|
|
606 // Egress :
|
|
|
607 // Self has acquired the lock -- Unlink Self from the cxq or EntryList.
|
|
|
608 // Normally we'll find Self on the EntryList .
|
|
|
609 // From the perspective of the lock owner (this thread), the
|
|
|
610 // EntryList is stable and cxq is prepend-only.
|
|
|
611 // The head of cxq is volatile but the interior is stable.
|
|
|
612 // In addition, Self.TState is stable.
|
|
|
613
|
|
|
614 assert (_owner == Self , "invariant") ;
|
|
|
615 assert (object() != NULL , "invariant") ;
|
|
|
616 // I'd like to write:
|
|
|
617 // guarantee (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
|
|
|
618 // but as we're at a safepoint that's not safe.
|
|
|
619
|
|
|
620 UnlinkAfterAcquire (Self, &node) ;
|
|
|
621 if (_succ == Self) _succ = NULL ;
|
|
|
622
|
|
|
623 assert (_succ != Self, "invariant") ;
|
|
|
624 if (_Responsible == Self) {
|
|
|
625 _Responsible = NULL ;
|
|
|
626 // Dekker pivot-point.
|
|
|
627 // Consider OrderAccess::storeload() here
|
|
|
628
|
|
|
629 // We may leave threads on cxq|EntryList without a designated
|
|
|
630 // "Responsible" thread. This is benign. When this thread subsequently
|
|
|
631 // exits the monitor it can "see" such preexisting "old" threads --
|
|
|
632 // threads that arrived on the cxq|EntryList before the fence, above --
|
|
|
633 // by LDing cxq|EntryList. Newly arrived threads -- that is, threads
|
|
|
634 // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
|
|
|
635 // non-null and elect a new "Responsible" timer thread.
|
|
|
636 //
|
|
|
637 // This thread executes:
|
|
|
638 // ST Responsible=null; MEMBAR (in enter epilog - here)
|
|
|
639 // LD cxq|EntryList (in subsequent exit)
|
|
|
640 //
|
|
|
641 // Entering threads in the slow/contended path execute:
|
|
|
642 // ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
|
|
|
643 // The (ST cxq; MEMBAR) is accomplished with CAS().
|
|
|
644 //
|
|
|
645 // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
|
|
|
646 // exit operation from floating above the ST Responsible=null.
|
|
|
647 //
|
|
|
648 // In *practice* however, EnterI() is always followed by some atomic
|
|
|
649 // operation such as the decrement of _count in ::enter(). Those atomics
|
|
|
650 // obviate the need for the explicit MEMBAR, above.
|
|
|
651 }
|
|
|
652
|
|
|
653 // We've acquired ownership with CAS().
|
|
|
654 // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
|
|
|
655 // But since the CAS() this thread may have also stored into _succ,
|
|
|
656 // EntryList, cxq or Responsible. These meta-data updates must be
|
|
|
657 // visible __before this thread subsequently drops the lock.
|
|
|
658 // Consider what could occur if we didn't enforce this constraint --
|
|
|
659 // STs to monitor meta-data and user-data could reorder with (become
|
|
|
660 // visible after) the ST in exit that drops ownership of the lock.
|
|
|
661 // Some other thread could then acquire the lock, but observe inconsistent
|
|
|
662 // or old monitor meta-data and heap data. That violates the JMM.
|
|
|
663 // To that end, the 1-0 exit() operation must have at least STST|LDST
|
|
|
664 // "release" barrier semantics. Specifically, there must be at least a
|
|
|
665 // STST|LDST barrier in exit() before the ST of null into _owner that drops
|
|
|
666 // the lock. The barrier ensures that changes to monitor meta-data and data
|
|
|
667 // protected by the lock will be visible before we release the lock, and
|
|
|
668 // therefore before some other thread (CPU) has a chance to acquire the lock.
|
|
|
669 // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
|
|
|
670 //
|
|
|
671 // Critically, any prior STs to _succ or EntryList must be visible before
|
|
|
672 // the ST of null into _owner in the *subsequent* (following) corresponding
|
|
|
673 // monitorexit. Recall too, that in 1-0 mode monitorexit does not necessarily
|
|
|
674 // execute a serializing instruction.
|
|
|
675
|
|
|
676 if (SyncFlags & 8) {
|
|
|
677 OrderAccess::fence() ;
|
|
|
678 }
|
|
|
679 return ;
|
|
|
680 }
|
|
|
681
|
|
|
682 // ReenterI() is a specialized inline form of the latter half of the
|
|
|
683 // contended slow-path from EnterI(). We use ReenterI() only for
|
|
|
684 // monitor reentry in wait().
|
|
|
685 //
|
|
|
686 // In the future we should reconcile EnterI() and ReenterI(), adding
|
|
|
687 // Knob_Reset and Knob_SpinAfterFutile support and restructuring the
|
|
|
688 // loop accordingly.
|
|
|
689
|
|
|
690 void ATTR ObjectMonitor::ReenterI (Thread * Self, ObjectWaiter * SelfNode) {
|
|
|
691 assert (Self != NULL , "invariant") ;
|
|
|
692 assert (SelfNode != NULL , "invariant") ;
|
|
|
693 assert (SelfNode->_thread == Self , "invariant") ;
|
|
|
694 assert (_waiters > 0 , "invariant") ;
|
|
|
695 assert (((oop)(object()))->mark() == markOopDesc::encode(this) , "invariant") ;
|
|
|
696 assert (((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
|
|
|
697 JavaThread * jt = (JavaThread *) Self ;
|
|
|
698
|
|
|
699 int nWakeups = 0 ;
|
|
|
700 for (;;) {
|
|
|
701 ObjectWaiter::TStates v = SelfNode->TState ;
|
|
|
702 guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
|
|
|
703 assert (_owner != Self, "invariant") ;
|
|
|
704
|
|
|
705 if (TryLock (Self) > 0) break ;
|
|
|
706 if (TrySpin (Self) > 0) break ;
|
|
|
707
|
|
|
708 TEVENT (Wait Reentry - parking) ;
|
|
|
709
|
|
|
710 // State transition wrappers around park() ...
|
|
|
711 // ReenterI() wisely defers state transitions until
|
|
|
712 // it's clear we must park the thread.
|
|
|
713 {
|
|
|
714 OSThreadContendState osts(Self->osthread());
|
|
|
715 ThreadBlockInVM tbivm(jt);
|
|
|
716
|
|
|
717 // cleared by handle_special_suspend_equivalent_condition()
|
|
|
718 // or java_suspend_self()
|
|
|
719 jt->set_suspend_equivalent();
|
|
|
720 if (SyncFlags & 1) {
|
|
|
721 Self->_ParkEvent->park ((jlong)1000) ;
|
|
|
722 } else {
|
|
|
723 Self->_ParkEvent->park () ;
|
|
|
724 }
|
|
|
725
|
|
|
726 // were we externally suspended while we were waiting?
|
|
|
727 for (;;) {
|
|
|
728 if (!ExitSuspendEquivalent (jt)) break ;
|
|
|
729 if (_succ == Self) { _succ = NULL; OrderAccess::fence(); }
|
|
|
730 jt->java_suspend_self();
|
|
|
731 jt->set_suspend_equivalent();
|
|
|
732 }
|
|
|
733 }
|
|
|
734
|
|
|
735 // Try again, but just so we distinguish between futile wakeups and
|
|
|
736 // successful wakeups. The following test isn't algorithmically
|
|
|
737 // necessary, but it helps us maintain sensible statistics.
|
|
|
738 if (TryLock(Self) > 0) break ;
|
|
|
739
|
|
|
740 // The lock is still contested.
|
|
|
741 // Keep a tally of the # of futile wakeups.
|
|
|
742 // Note that the counter is not protected by a lock or updated by atomics.
|
|
|
743 // That is by design - we trade "lossy" counters which are exposed to
|
|
|
744 // races during updates for a lower probe effect.
|
|
|
745 TEVENT (Wait Reentry - futile wakeup) ;
|
|
|
746 ++ nWakeups ;
|
|
|
747
|
|
|
748 // Assuming this is not a spurious wakeup we'll normally
|
|
|
749 // find that _succ == Self.
|
|
|
750 if (_succ == Self) _succ = NULL ;
|
|
|
751
|
|
|
752 // Invariant: after clearing _succ a contending thread
|
|
|
753 // *must* retry _owner before parking.
|
|
|
754 OrderAccess::fence() ;
|
|
|
755
|
|
|
756 if (ObjectMonitor::_sync_FutileWakeups != NULL) {
|
|
|
757 ObjectMonitor::_sync_FutileWakeups->inc() ;
|
|
|
758 }
|
|
|
759 }
|
|
|
760
|
|
|
761 // Self has acquired the lock -- Unlink Self from the cxq or EntryList .
|
|
|
762 // Normally we'll find Self on the EntryList.
|
|
|
763 // Unlinking from the EntryList is constant-time and atomic-free.
|
|
|
764 // From the perspective of the lock owner (this thread), the
|
|
|
765 // EntryList is stable and cxq is prepend-only.
|
|
|
766 // The head of cxq is volatile but the interior is stable.
|
|
|
767 // In addition, Self.TState is stable.
|
|
|
768
|
|
|
769 assert (_owner == Self, "invariant") ;
|
|
|
770 assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
|
|
|
771 UnlinkAfterAcquire (Self, SelfNode) ;
|
|
|
772 if (_succ == Self) _succ = NULL ;
|
|
|
773 assert (_succ != Self, "invariant") ;
|
|
|
774 SelfNode->TState = ObjectWaiter::TS_RUN ;
|
|
|
775 OrderAccess::fence() ; // see comments at the end of EnterI()
|
|
|
776 }
|
|
|
777
|
|
|
778 // after the thread acquires the lock in ::enter(). Equally, we could defer
|
|
|
779 // unlinking the thread until ::exit()-time.
|
|
|
780
|
|
|
781 void ObjectMonitor::UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode)
|
|
|
782 {
|
|
|
783 assert (_owner == Self, "invariant") ;
|
|
|
784 assert (SelfNode->_thread == Self, "invariant") ;
|
|
|
785
|
|
|
786 if (SelfNode->TState == ObjectWaiter::TS_ENTER) {
|
|
|
787 // Normal case: remove Self from the DLL EntryList .
|
|
|
788 // This is a constant-time operation.
|
|
|
789 ObjectWaiter * nxt = SelfNode->_next ;
|
|
|
790 ObjectWaiter * prv = SelfNode->_prev ;
|
|
|
791 if (nxt != NULL) nxt->_prev = prv ;
|
|
|
792 if (prv != NULL) prv->_next = nxt ;
|
|
|
793 if (SelfNode == _EntryList ) _EntryList = nxt ;
|
|
|
794 assert (nxt == NULL || nxt->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
795 assert (prv == NULL || prv->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
796 TEVENT (Unlink from EntryList) ;
|
|
|
797 } else {
|
|
|
798 guarantee (SelfNode->TState == ObjectWaiter::TS_CXQ, "invariant") ;
|
|
|
799 // Inopportune interleaving -- Self is still on the cxq.
|
|
|
800 // This usually means the enqueue of self raced an exiting thread.
|
|
|
801 // Normally we'll find Self near the front of the cxq, so
|
|
|
802 // dequeueing is typically fast. If needbe we can accelerate
|
|
|
803 // this with some MCS/CHL-like bidirectional list hints and advisory
|
|
|
804 // back-links so dequeueing from the interior will normally operate
|
|
|
805 // in constant-time.
|
|
|
806 // Dequeue Self from either the head (with CAS) or from the interior
|
|
|
807 // with a linear-time scan and normal non-atomic memory operations.
|
|
|
808 // CONSIDER: if Self is on the cxq then simply drain cxq into EntryList
|
|
|
809 // and then unlink Self from EntryList. We have to drain eventually,
|
|
|
810 // so it might as well be now.
|
|
|
811
|
|
|
812 ObjectWaiter * v = _cxq ;
|
|
|
813 assert (v != NULL, "invariant") ;
|
|
|
814 if (v != SelfNode || Atomic::cmpxchg_ptr (SelfNode->_next, &_cxq, v) != v) {
|
|
|
815 // The CAS above can fail from interference IFF a "RAT" arrived.
|
|
|
816 // In that case Self must be in the interior and can no longer be
|
|
|
817 // at the head of cxq.
|
|
|
818 if (v == SelfNode) {
|
|
|
819 assert (_cxq != v, "invariant") ;
|
|
|
820 v = _cxq ; // CAS above failed - start scan at head of list
|
|
|
821 }
|
|
|
822 ObjectWaiter * p ;
|
|
|
823 ObjectWaiter * q = NULL ;
|
|
|
824 for (p = v ; p != NULL && p != SelfNode; p = p->_next) {
|
|
|
825 q = p ;
|
|
|
826 assert (p->TState == ObjectWaiter::TS_CXQ, "invariant") ;
|
|
|
827 }
|
|
|
828 assert (v != SelfNode, "invariant") ;
|
|
|
829 assert (p == SelfNode, "Node not found on cxq") ;
|
|
|
830 assert (p != _cxq, "invariant") ;
|
|
|
831 assert (q != NULL, "invariant") ;
|
|
|
832 assert (q->_next == p, "invariant") ;
|
|
|
833 q->_next = p->_next ;
|
|
|
834 }
|
|
|
835 TEVENT (Unlink from cxq) ;
|
|
|
836 }
|
|
|
837
|
|
|
838 // Diagnostic hygiene ...
|
|
|
839 SelfNode->_prev = (ObjectWaiter *) 0xBAD ;
|
|
|
840 SelfNode->_next = (ObjectWaiter *) 0xBAD ;
|
|
|
841 SelfNode->TState = ObjectWaiter::TS_RUN ;
|
|
|
842 }
|
|
|
843
|
|
|
844 // -----------------------------------------------------------------------------
|
|
|
845 // Exit support
|
|
|
846 //
|
|
|
847 // exit()
|
|
|
848 // ~~~~~~
|
|
|
849 // Note that the collector can't reclaim the objectMonitor or deflate
|
|
|
850 // the object out from underneath the thread calling ::exit() as the
|
|
|
851 // thread calling ::exit() never transitions to a stable state.
|
|
|
852 // This inhibits GC, which in turn inhibits asynchronous (and
|
|
|
853 // inopportune) reclamation of "this".
|
|
|
854 //
|
|
|
855 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
|
|
|
856 // There's one exception to the claim above, however. EnterI() can call
|
|
|
857 // exit() to drop a lock if the acquirer has been externally suspended.
|
|
|
858 // In that case exit() is called with _thread_state as _thread_blocked,
|
|
|
859 // but the monitor's _count field is > 0, which inhibits reclamation.
|
|
|
860 //
|
|
|
861 // 1-0 exit
|
|
|
862 // ~~~~~~~~
|
|
|
863 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
|
|
|
864 // the fast-path operators have been optimized so the common ::exit()
|
|
|
865 // operation is 1-0. See i486.ad fast_unlock(), for instance.
|
|
|
866 // The code emitted by fast_unlock() elides the usual MEMBAR. This
|
|
|
867 // greatly improves latency -- MEMBAR and CAS having considerable local
|
|
|
868 // latency on modern processors -- but at the cost of "stranding". Absent the
|
|
|
869 // MEMBAR, a thread in fast_unlock() can race a thread in the slow
|
|
|
870 // ::enter() path, resulting in the entering thread being stranding
|
|
|
871 // and a progress-liveness failure. Stranding is extremely rare.
|
|
|
872 // We use timers (timed park operations) & periodic polling to detect
|
|
|
873 // and recover from stranding. Potentially stranded threads periodically
|
|
|
874 // wake up and poll the lock. See the usage of the _Responsible variable.
|
|
|
875 //
|
|
|
876 // The CAS() in enter provides for safety and exclusion, while the CAS or
|
|
|
877 // MEMBAR in exit provides for progress and avoids stranding. 1-0 locking
|
|
|
878 // eliminates the CAS/MEMBAR from the exist path, but it admits stranding.
|
|
|
879 // We detect and recover from stranding with timers.
|
|
|
880 //
|
|
|
881 // If a thread transiently strands it'll park until (a) another
|
|
|
882 // thread acquires the lock and then drops the lock, at which time the
|
|
|
883 // exiting thread will notice and unpark the stranded thread, or, (b)
|
|
|
884 // the timer expires. If the lock is high traffic then the stranding latency
|
|
|
885 // will be low due to (a). If the lock is low traffic then the odds of
|
|
|
886 // stranding are lower, although the worst-case stranding latency
|
|
|
887 // is longer. Critically, we don't want to put excessive load in the
|
|
|
888 // platform's timer subsystem. We want to minimize both the timer injection
|
|
|
889 // rate (timers created/sec) as well as the number of timers active at
|
|
|
890 // any one time. (more precisely, we want to minimize timer-seconds, which is
|
|
|
891 // the integral of the # of active timers at any instant over time).
|
|
|
892 // Both impinge on OS scalability. Given that, at most one thread parked on
|
|
|
893 // a monitor will use a timer.
|
|
|
894
|
|
|
895 void ATTR ObjectMonitor::exit(TRAPS) {
|
|
|
896 Thread * Self = THREAD ;
|
|
|
897 if (THREAD != _owner) {
|
|
|
898 if (THREAD->is_lock_owned((address) _owner)) {
|
|
|
899 // Transmute _owner from a BasicLock pointer to a Thread address.
|
|
|
900 // We don't need to hold _mutex for this transition.
|
|
|
901 // Non-null to Non-null is safe as long as all readers can
|
|
|
902 // tolerate either flavor.
|
|
|
903 assert (_recursions == 0, "invariant") ;
|
|
|
904 _owner = THREAD ;
|
|
|
905 _recursions = 0 ;
|
|
|
906 OwnerIsThread = 1 ;
|
|
|
907 } else {
|
|
|
908 // NOTE: we need to handle unbalanced monitor enter/exit
|
|
|
909 // in native code by throwing an exception.
|
|
|
910 // TODO: Throw an IllegalMonitorStateException ?
|
|
|
911 TEVENT (Exit - Throw IMSX) ;
|
|
|
912 assert(false, "Non-balanced monitor enter/exit!");
|
|
|
913 if (false) {
|
|
|
914 THROW(vmSymbols::java_lang_IllegalMonitorStateException());
|
|
|
915 }
|
|
|
916 return;
|
|
|
917 }
|
|
|
918 }
|
|
|
919
|
|
|
920 if (_recursions != 0) {
|
|
|
921 _recursions--; // this is simple recursive enter
|
|
|
922 TEVENT (Inflated exit - recursive) ;
|
|
|
923 return ;
|
|
|
924 }
|
|
|
925
|
|
|
926 // Invariant: after setting Responsible=null an thread must execute
|
|
|
927 // a MEMBAR or other serializing instruction before fetching EntryList|cxq.
|
|
|
928 if ((SyncFlags & 4) == 0) {
|
|
|
929 _Responsible = NULL ;
|
|
|
930 }
|
|
|
931
|
|
|
932 for (;;) {
|
|
|
933 assert (THREAD == _owner, "invariant") ;
|
|
|
934
|
|
|
935
|
|
|
936 if (Knob_ExitPolicy == 0) {
|
|
|
937 // release semantics: prior loads and stores from within the critical section
|
|
|
938 // must not float (reorder) past the following store that drops the lock.
|
|
|
939 // On SPARC that requires MEMBAR #loadstore|#storestore.
|
|
|
940 // But of course in TSO #loadstore|#storestore is not required.
|
|
|
941 // I'd like to write one of the following:
|
|
|
942 // A. OrderAccess::release() ; _owner = NULL
|
|
|
943 // B. OrderAccess::loadstore(); OrderAccess::storestore(); _owner = NULL;
|
|
|
944 // Unfortunately OrderAccess::release() and OrderAccess::loadstore() both
|
|
|
945 // store into a _dummy variable. That store is not needed, but can result
|
|
|
946 // in massive wasteful coherency traffic on classic SMP systems.
|
|
|
947 // Instead, I use release_store(), which is implemented as just a simple
|
|
|
948 // ST on x64, x86 and SPARC.
|
|
|
949 OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock
|
|
|
950 OrderAccess::storeload() ; // See if we need to wake a successor
|
|
|
951 if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
|
|
|
952 TEVENT (Inflated exit - simple egress) ;
|
|
|
953 return ;
|
|
|
954 }
|
|
|
955 TEVENT (Inflated exit - complex egress) ;
|
|
|
956
|
|
|
957 // Normally the exiting thread is responsible for ensuring succession,
|
|
|
958 // but if other successors are ready or other entering threads are spinning
|
|
|
959 // then this thread can simply store NULL into _owner and exit without
|
|
|
960 // waking a successor. The existence of spinners or ready successors
|
|
|
961 // guarantees proper succession (liveness). Responsibility passes to the
|
|
|
962 // ready or running successors. The exiting thread delegates the duty.
|
|
|
963 // More precisely, if a successor already exists this thread is absolved
|
|
|
964 // of the responsibility of waking (unparking) one.
|
|
|
965 //
|
|
|
966 // The _succ variable is critical to reducing futile wakeup frequency.
|
|
|
967 // _succ identifies the "heir presumptive" thread that has been made
|
|
|
968 // ready (unparked) but that has not yet run. We need only one such
|
|
|
969 // successor thread to guarantee progress.
|
|
|
970 // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
|
|
|
971 // section 3.3 "Futile Wakeup Throttling" for details.
|
|
|
972 //
|
|
|
973 // Note that spinners in Enter() also set _succ non-null.
|
|
|
974 // In the current implementation spinners opportunistically set
|
|
|
975 // _succ so that exiting threads might avoid waking a successor.
|
|
|
976 // Another less appealing alternative would be for the exiting thread
|
|
|
977 // to drop the lock and then spin briefly to see if a spinner managed
|
|
|
978 // to acquire the lock. If so, the exiting thread could exit
|
|
|
979 // immediately without waking a successor, otherwise the exiting
|
|
|
980 // thread would need to dequeue and wake a successor.
|
|
|
981 // (Note that we'd need to make the post-drop spin short, but no
|
|
|
982 // shorter than the worst-case round-trip cache-line migration time.
|
|
|
983 // The dropped lock needs to become visible to the spinner, and then
|
|
|
984 // the acquisition of the lock by the spinner must become visible to
|
|
|
985 // the exiting thread).
|
|
|
986 //
|
|
|
987
|
|
|
988 // It appears that an heir-presumptive (successor) must be made ready.
|
|
|
989 // Only the current lock owner can manipulate the EntryList or
|
|
|
990 // drain _cxq, so we need to reacquire the lock. If we fail
|
|
|
991 // to reacquire the lock the responsibility for ensuring succession
|
|
|
992 // falls to the new owner.
|
|
|
993 //
|
|
|
994 if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
|
|
|
995 return ;
|
|
|
996 }
|
|
|
997 TEVENT (Exit - Reacquired) ;
|
|
|
998 } else {
|
|
|
999 if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
|
|
|
1000 OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock
|
|
|
1001 OrderAccess::storeload() ;
|
|
|
1002 // Ratify the previously observed values.
|
|
|
1003 if (_cxq == NULL || _succ != NULL) {
|
|
|
1004 TEVENT (Inflated exit - simple egress) ;
|
|
|
1005 return ;
|
|
|
1006 }
|
|
|
1007
|
|
|
1008 // inopportune interleaving -- the exiting thread (this thread)
|
|
|
1009 // in the fast-exit path raced an entering thread in the slow-enter
|
|
|
1010 // path.
|
|
|
1011 // We have two choices:
|
|
|
1012 // A. Try to reacquire the lock.
|
|
|
1013 // If the CAS() fails return immediately, otherwise
|
|
|
1014 // we either restart/rerun the exit operation, or simply
|
|
|
1015 // fall-through into the code below which wakes a successor.
|
|
|
1016 // B. If the elements forming the EntryList|cxq are TSM
|
|
|
1017 // we could simply unpark() the lead thread and return
|
|
|
1018 // without having set _succ.
|
|
|
1019 if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
|
|
|
1020 TEVENT (Inflated exit - reacquired succeeded) ;
|
|
|
1021 return ;
|
|
|
1022 }
|
|
|
1023 TEVENT (Inflated exit - reacquired failed) ;
|
|
|
1024 } else {
|
|
|
1025 TEVENT (Inflated exit - complex egress) ;
|
|
|
1026 }
|
|
|
1027 }
|
|
|
1028
|
|
|
1029 guarantee (_owner == THREAD, "invariant") ;
|
|
|
1030
|
|
|
1031 ObjectWaiter * w = NULL ;
|
|
|
1032 int QMode = Knob_QMode ;
|
|
|
1033
|
|
|
1034 if (QMode == 2 && _cxq != NULL) {
|
|
|
1035 // QMode == 2 : cxq has precedence over EntryList.
|
|
|
1036 // Try to directly wake a successor from the cxq.
|
|
|
1037 // If successful, the successor will need to unlink itself from cxq.
|
|
|
1038 w = _cxq ;
|
|
|
1039 assert (w != NULL, "invariant") ;
|
|
|
1040 assert (w->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
|
|
|
1041 ExitEpilog (Self, w) ;
|
|
|
1042 return ;
|
|
|
1043 }
|
|
|
1044
|
|
|
1045 if (QMode == 3 && _cxq != NULL) {
|
|
|
1046 // Aggressively drain cxq into EntryList at the first opportunity.
|
|
|
1047 // This policy ensure that recently-run threads live at the head of EntryList.
|
|
|
1048 // Drain _cxq into EntryList - bulk transfer.
|
|
|
1049 // First, detach _cxq.
|
|
|
1050 // The following loop is tantamount to: w = swap (&cxq, NULL)
|
|
|
1051 w = _cxq ;
|
|
|
1052 for (;;) {
|
|
|
1053 assert (w != NULL, "Invariant") ;
|
|
|
1054 ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
|
|
|
1055 if (u == w) break ;
|
|
|
1056 w = u ;
|
|
|
1057 }
|
|
|
1058 assert (w != NULL , "invariant") ;
|
|
|
1059
|
|
|
1060 ObjectWaiter * q = NULL ;
|
|
|
1061 ObjectWaiter * p ;
|
|
|
1062 for (p = w ; p != NULL ; p = p->_next) {
|
|
|
1063 guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
|
|
|
1064 p->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1065 p->_prev = q ;
|
|
|
1066 q = p ;
|
|
|
1067 }
|
|
|
1068
|
|
|
1069 // Append the RATs to the EntryList
|
|
|
1070 // TODO: organize EntryList as a CDLL so we can locate the tail in constant-time.
|
|
|
1071 ObjectWaiter * Tail ;
|
|
|
1072 for (Tail = _EntryList ; Tail != NULL && Tail->_next != NULL ; Tail = Tail->_next) ;
|
|
|
1073 if (Tail == NULL) {
|
|
|
1074 _EntryList = w ;
|
|
|
1075 } else {
|
|
|
1076 Tail->_next = w ;
|
|
|
1077 w->_prev = Tail ;
|
|
|
1078 }
|
|
|
1079
|
|
|
1080 // Fall thru into code that tries to wake a successor from EntryList
|
|
|
1081 }
|
|
|
1082
|
|
|
1083 if (QMode == 4 && _cxq != NULL) {
|
|
|
1084 // Aggressively drain cxq into EntryList at the first opportunity.
|
|
|
1085 // This policy ensure that recently-run threads live at the head of EntryList.
|
|
|
1086
|
|
|
1087 // Drain _cxq into EntryList - bulk transfer.
|
|
|
1088 // First, detach _cxq.
|
|
|
1089 // The following loop is tantamount to: w = swap (&cxq, NULL)
|
|
|
1090 w = _cxq ;
|
|
|
1091 for (;;) {
|
|
|
1092 assert (w != NULL, "Invariant") ;
|
|
|
1093 ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
|
|
|
1094 if (u == w) break ;
|
|
|
1095 w = u ;
|
|
|
1096 }
|
|
|
1097 assert (w != NULL , "invariant") ;
|
|
|
1098
|
|
|
1099 ObjectWaiter * q = NULL ;
|
|
|
1100 ObjectWaiter * p ;
|
|
|
1101 for (p = w ; p != NULL ; p = p->_next) {
|
|
|
1102 guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
|
|
|
1103 p->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1104 p->_prev = q ;
|
|
|
1105 q = p ;
|
|
|
1106 }
|
|
|
1107
|
|
|
1108 // Prepend the RATs to the EntryList
|
|
|
1109 if (_EntryList != NULL) {
|
|
|
1110 q->_next = _EntryList ;
|
|
|
1111 _EntryList->_prev = q ;
|
|
|
1112 }
|
|
|
1113 _EntryList = w ;
|
|
|
1114
|
|
|
1115 // Fall thru into code that tries to wake a successor from EntryList
|
|
|
1116 }
|
|
|
1117
|
|
|
1118 w = _EntryList ;
|
|
|
1119 if (w != NULL) {
|
|
|
1120 // I'd like to write: guarantee (w->_thread != Self).
|
|
|
1121 // But in practice an exiting thread may find itself on the EntryList.
|
|
|
1122 // Lets say thread T1 calls O.wait(). Wait() enqueues T1 on O's waitset and
|
|
|
1123 // then calls exit(). Exit release the lock by setting O._owner to NULL.
|
|
|
1124 // Lets say T1 then stalls. T2 acquires O and calls O.notify(). The
|
|
|
1125 // notify() operation moves T1 from O's waitset to O's EntryList. T2 then
|
|
|
1126 // release the lock "O". T2 resumes immediately after the ST of null into
|
|
|
1127 // _owner, above. T2 notices that the EntryList is populated, so it
|
|
|
1128 // reacquires the lock and then finds itself on the EntryList.
|
|
|
1129 // Given all that, we have to tolerate the circumstance where "w" is
|
|
|
1130 // associated with Self.
|
|
|
1131 assert (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
1132 ExitEpilog (Self, w) ;
|
|
|
1133 return ;
|
|
|
1134 }
|
|
|
1135
|
|
|
1136 // If we find that both _cxq and EntryList are null then just
|
|
|
1137 // re-run the exit protocol from the top.
|
|
|
1138 w = _cxq ;
|
|
|
1139 if (w == NULL) continue ;
|
|
|
1140
|
|
|
1141 // Drain _cxq into EntryList - bulk transfer.
|
|
|
1142 // First, detach _cxq.
|
|
|
1143 // The following loop is tantamount to: w = swap (&cxq, NULL)
|
|
|
1144 for (;;) {
|
|
|
1145 assert (w != NULL, "Invariant") ;
|
|
|
1146 ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
|
|
|
1147 if (u == w) break ;
|
|
|
1148 w = u ;
|
|
|
1149 }
|
|
|
1150 TEVENT (Inflated exit - drain cxq into EntryList) ;
|
|
|
1151
|
|
|
1152 assert (w != NULL , "invariant") ;
|
|
|
1153 assert (_EntryList == NULL , "invariant") ;
|
|
|
1154
|
|
|
1155 // Convert the LIFO SLL anchored by _cxq into a DLL.
|
|
|
1156 // The list reorganization step operates in O(LENGTH(w)) time.
|
|
|
1157 // It's critical that this step operate quickly as
|
|
|
1158 // "Self" still holds the outer-lock, restricting parallelism
|
|
|
1159 // and effectively lengthening the critical section.
|
|
|
1160 // Invariant: s chases t chases u.
|
|
|
1161 // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
|
|
|
1162 // we have faster access to the tail.
|
|
|
1163
|
|
|
1164 if (QMode == 1) {
|
|
|
1165 // QMode == 1 : drain cxq to EntryList, reversing order
|
|
|
1166 // We also reverse the order of the list.
|
|
|
1167 ObjectWaiter * s = NULL ;
|
|
|
1168 ObjectWaiter * t = w ;
|
|
|
1169 ObjectWaiter * u = NULL ;
|
|
|
1170 while (t != NULL) {
|
|
|
1171 guarantee (t->TState == ObjectWaiter::TS_CXQ, "invariant") ;
|
|
|
1172 t->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1173 u = t->_next ;
|
|
|
1174 t->_prev = u ;
|
|
|
1175 t->_next = s ;
|
|
|
1176 s = t;
|
|
|
1177 t = u ;
|
|
|
1178 }
|
|
|
1179 _EntryList = s ;
|
|
|
1180 assert (s != NULL, "invariant") ;
|
|
|
1181 } else {
|
|
|
1182 // QMode == 0 or QMode == 2
|
|
|
1183 _EntryList = w ;
|
|
|
1184 ObjectWaiter * q = NULL ;
|
|
|
1185 ObjectWaiter * p ;
|
|
|
1186 for (p = w ; p != NULL ; p = p->_next) {
|
|
|
1187 guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
|
|
|
1188 p->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1189 p->_prev = q ;
|
|
|
1190 q = p ;
|
|
|
1191 }
|
|
|
1192 }
|
|
|
1193
|
|
|
1194 // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = NULL
|
|
|
1195 // The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
|
|
|
1196
|
|
|
1197 // See if we can abdicate to a spinner instead of waking a thread.
|
|
|
1198 // A primary goal of the implementation is to reduce the
|
|
|
1199 // context-switch rate.
|
|
|
1200 if (_succ != NULL) continue;
|
|
|
1201
|
|
|
1202 w = _EntryList ;
|
|
|
1203 if (w != NULL) {
|
|
|
1204 guarantee (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
1205 ExitEpilog (Self, w) ;
|
|
|
1206 return ;
|
|
|
1207 }
|
|
|
1208 }
|
|
|
1209 }
|
|
|
1210
|
|
|
1211 // ExitSuspendEquivalent:
|
|
|
1212 // A faster alternate to handle_special_suspend_equivalent_condition()
|
|
|
1213 //
|
|
|
1214 // handle_special_suspend_equivalent_condition() unconditionally
|
|
|
1215 // acquires the SR_lock. On some platforms uncontended MutexLocker()
|
|
|
1216 // operations have high latency. Note that in ::enter() we call HSSEC
|
|
|
1217 // while holding the monitor, so we effectively lengthen the critical sections.
|
|
|
1218 //
|
|
|
1219 // There are a number of possible solutions:
|
|
|
1220 //
|
|
|
1221 // A. To ameliorate the problem we might also defer state transitions
|
|
|
1222 // to as late as possible -- just prior to parking.
|
|
|
1223 // Given that, we'd call HSSEC after having returned from park(),
|
|
|
1224 // but before attempting to acquire the monitor. This is only a
|
|
|
1225 // partial solution. It avoids calling HSSEC while holding the
|
|
|
1226 // monitor (good), but it still increases successor reacquisition latency --
|
|
|
1227 // the interval between unparking a successor and the time the successor
|
|
|
1228 // resumes and retries the lock. See ReenterI(), which defers state transitions.
|
|
|
1229 // If we use this technique we can also avoid EnterI()-exit() loop
|
|
|
1230 // in ::enter() where we iteratively drop the lock and then attempt
|
|
|
1231 // to reacquire it after suspending.
|
|
|
1232 //
|
|
|
1233 // B. In the future we might fold all the suspend bits into a
|
|
|
1234 // composite per-thread suspend flag and then update it with CAS().
|
|
|
1235 // Alternately, a Dekker-like mechanism with multiple variables
|
|
|
1236 // would suffice:
|
|
|
1237 // ST Self->_suspend_equivalent = false
|
|
|
1238 // MEMBAR
|
|
|
1239 // LD Self_>_suspend_flags
|
|
|
1240 //
|
|
|
1241
|
|
|
1242
|
|
|
1243 bool ObjectMonitor::ExitSuspendEquivalent (JavaThread * jSelf) {
|
|
|
1244 int Mode = Knob_FastHSSEC ;
|
|
|
1245 if (Mode && !jSelf->is_external_suspend()) {
|
|
|
1246 assert (jSelf->is_suspend_equivalent(), "invariant") ;
|
|
|
1247 jSelf->clear_suspend_equivalent() ;
|
|
|
1248 if (2 == Mode) OrderAccess::storeload() ;
|
|
|
1249 if (!jSelf->is_external_suspend()) return false ;
|
|
|
1250 // We raced a suspension -- fall thru into the slow path
|
|
|
1251 TEVENT (ExitSuspendEquivalent - raced) ;
|
|
|
1252 jSelf->set_suspend_equivalent() ;
|
|
|
1253 }
|
|
|
1254 return jSelf->handle_special_suspend_equivalent_condition() ;
|
|
|
1255 }
|
|
|
1256
|
|
|
1257
|
|
|
1258 void ObjectMonitor::ExitEpilog (Thread * Self, ObjectWaiter * Wakee) {
|
|
|
1259 assert (_owner == Self, "invariant") ;
|
|
|
1260
|
|
|
1261 // Exit protocol:
|
|
|
1262 // 1. ST _succ = wakee
|
|
|
1263 // 2. membar #loadstore|#storestore;
|
|
|
1264 // 2. ST _owner = NULL
|
|
|
1265 // 3. unpark(wakee)
|
|
|
1266
|
|
|
1267 _succ = Knob_SuccEnabled ? Wakee->_thread : NULL ;
|
|
|
1268 ParkEvent * Trigger = Wakee->_event ;
|
|
|
1269
|
|
|
1270 // Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
|
|
|
1271 // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
|
|
|
1272 // out-of-scope (non-extant).
|
|
|
1273 Wakee = NULL ;
|
|
|
1274
|
|
|
1275 // Drop the lock
|
|
|
1276 OrderAccess::release_store_ptr (&_owner, NULL) ;
|
|
|
1277 OrderAccess::fence() ; // ST _owner vs LD in unpark()
|
|
|
1278
|
|
|
1279 if (SafepointSynchronize::do_call_back()) {
|
|
|
1280 TEVENT (unpark before SAFEPOINT) ;
|
|
|
1281 }
|
|
|
1282
|
|
|
1283 DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
|
|
|
1284 Trigger->unpark() ;
|
|
|
1285
|
|
|
1286 // Maintain stats and report events to JVMTI
|
|
|
1287 if (ObjectMonitor::_sync_Parks != NULL) {
|
|
|
1288 ObjectMonitor::_sync_Parks->inc() ;
|
|
|
1289 }
|
|
|
1290 }
|
|
|
1291
|
|
|
1292
|
|
|
1293 // -----------------------------------------------------------------------------
|
|
|
1294 // Class Loader deadlock handling.
|
|
|
1295 //
|
|
|
1296 // complete_exit exits a lock returning recursion count
|
|
|
1297 // complete_exit/reenter operate as a wait without waiting
|
|
|
1298 // complete_exit requires an inflated monitor
|
|
|
1299 // The _owner field is not always the Thread addr even with an
|
|
|
1300 // inflated monitor, e.g. the monitor can be inflated by a non-owning
|
|
|
1301 // thread due to contention.
|
|
|
1302 intptr_t ObjectMonitor::complete_exit(TRAPS) {
|
|
|
1303 Thread * const Self = THREAD;
|
|
|
1304 assert(Self->is_Java_thread(), "Must be Java thread!");
|
|
|
1305 JavaThread *jt = (JavaThread *)THREAD;
|
|
|
1306
|
|
|
1307 DeferredInitialize();
|
|
|
1308
|
|
|
1309 if (THREAD != _owner) {
|
|
|
1310 if (THREAD->is_lock_owned ((address)_owner)) {
|
|
|
1311 assert(_recursions == 0, "internal state error");
|
|
|
1312 _owner = THREAD ; /* Convert from basiclock addr to Thread addr */
|
|
|
1313 _recursions = 0 ;
|
|
|
1314 OwnerIsThread = 1 ;
|
|
|
1315 }
|
|
|
1316 }
|
|
|
1317
|
|
|
1318 guarantee(Self == _owner, "complete_exit not owner");
|
|
|
1319 intptr_t save = _recursions; // record the old recursion count
|
|
|
1320 _recursions = 0; // set the recursion level to be 0
|
|
|
1321 exit (Self) ; // exit the monitor
|
|
|
1322 guarantee (_owner != Self, "invariant");
|
|
|
1323 return save;
|
|
|
1324 }
|
|
|
1325
|
|
|
1326 // reenter() enters a lock and sets recursion count
|
|
|
1327 // complete_exit/reenter operate as a wait without waiting
|
|
|
1328 void ObjectMonitor::reenter(intptr_t recursions, TRAPS) {
|
|
|
1329 Thread * const Self = THREAD;
|
|
|
1330 assert(Self->is_Java_thread(), "Must be Java thread!");
|
|
|
1331 JavaThread *jt = (JavaThread *)THREAD;
|
|
|
1332
|
|
|
1333 guarantee(_owner != Self, "reenter already owner");
|
|
|
1334 enter (THREAD); // enter the monitor
|
|
|
1335 guarantee (_recursions == 0, "reenter recursion");
|
|
|
1336 _recursions = recursions;
|
|
|
1337 return;
|
|
|
1338 }
|
|
|
1339
|
|
|
1340
|
|
|
1341 // -----------------------------------------------------------------------------
|
|
|
1342 // A macro is used below because there may already be a pending
|
|
|
1343 // exception which should not abort the execution of the routines
|
|
|
1344 // which use this (which is why we don't put this into check_slow and
|
|
|
1345 // call it with a CHECK argument).
|
|
|
1346
|
|
|
1347 #define CHECK_OWNER() \
|
|
|
1348 do { \
|
|
|
1349 if (THREAD != _owner) { \
|
|
|
1350 if (THREAD->is_lock_owned((address) _owner)) { \
|
|
|
1351 _owner = THREAD ; /* Convert from basiclock addr to Thread addr */ \
|
|
|
1352 _recursions = 0; \
|
|
|
1353 OwnerIsThread = 1 ; \
|
|
|
1354 } else { \
|
|
|
1355 TEVENT (Throw IMSX) ; \
|
|
|
1356 THROW(vmSymbols::java_lang_IllegalMonitorStateException()); \
|
|
|
1357 } \
|
|
|
1358 } \
|
|
|
1359 } while (false)
|
|
|
1360
|
|
|
1361 // check_slow() is a misnomer. It's called to simply to throw an IMSX exception.
|
|
|
1362 // TODO-FIXME: remove check_slow() -- it's likely dead.
|
|
|
1363
|
|
|
1364 void ObjectMonitor::check_slow(TRAPS) {
|
|
|
1365 TEVENT (check_slow - throw IMSX) ;
|
|
|
1366 assert(THREAD != _owner && !THREAD->is_lock_owned((address) _owner), "must not be owner");
|
|
|
1367 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), "current thread not owner");
|
|
|
1368 }
|
|
|
1369
|
|
|
1370 static int Adjust (volatile int * adr, int dx) {
|
|
|
1371 int v ;
|
|
|
1372 for (v = *adr ; Atomic::cmpxchg (v + dx, adr, v) != v; v = *adr) ;
|
|
|
1373 return v ;
|
|
|
1374 }
|
|
|
1375 // -----------------------------------------------------------------------------
|
|
|
1376 // Wait/Notify/NotifyAll
|
|
|
1377 //
|
|
|
1378 // Note: a subset of changes to ObjectMonitor::wait()
|
|
|
1379 // will need to be replicated in complete_exit above
|
|
|
1380 void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
|
|
|
1381 Thread * const Self = THREAD ;
|
|
|
1382 assert(Self->is_Java_thread(), "Must be Java thread!");
|
|
|
1383 JavaThread *jt = (JavaThread *)THREAD;
|
|
|
1384
|
|
|
1385 DeferredInitialize () ;
|
|
|
1386
|
|
|
1387 // Throw IMSX or IEX.
|
|
|
1388 CHECK_OWNER();
|
|
|
1389
|
|
|
1390 // check for a pending interrupt
|
|
|
1391 if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
|
|
|
1392 // post monitor waited event. Note that this is past-tense, we are done waiting.
|
|
|
1393 if (JvmtiExport::should_post_monitor_waited()) {
|
|
|
1394 // Note: 'false' parameter is passed here because the
|
|
|
1395 // wait was not timed out due to thread interrupt.
|
|
|
1396 JvmtiExport::post_monitor_waited(jt, this, false);
|
|
|
1397 }
|
|
|
1398 TEVENT (Wait - Throw IEX) ;
|
|
|
1399 THROW(vmSymbols::java_lang_InterruptedException());
|
|
|
1400 return ;
|
|
|
1401 }
|
|
|
1402 TEVENT (Wait) ;
|
|
|
1403
|
|
|
1404 assert (Self->_Stalled == 0, "invariant") ;
|
|
|
1405 Self->_Stalled = intptr_t(this) ;
|
|
|
1406 jt->set_current_waiting_monitor(this);
|
|
|
1407
|
|
|
1408 // create a node to be put into the queue
|
|
|
1409 // Critically, after we reset() the event but prior to park(), we must check
|
|
|
1410 // for a pending interrupt.
|
|
|
1411 ObjectWaiter node(Self);
|
|
|
1412 node.TState = ObjectWaiter::TS_WAIT ;
|
|
|
1413 Self->_ParkEvent->reset() ;
|
|
|
1414 OrderAccess::fence(); // ST into Event; membar ; LD interrupted-flag
|
|
|
1415
|
|
|
1416 // Enter the waiting queue, which is a circular doubly linked list in this case
|
|
|
1417 // but it could be a priority queue or any data structure.
|
|
|
1418 // _WaitSetLock protects the wait queue. Normally the wait queue is accessed only
|
|
|
1419 // by the the owner of the monitor *except* in the case where park()
|
|
|
1420 // returns because of a timeout of interrupt. Contention is exceptionally rare
|
|
|
1421 // so we use a simple spin-lock instead of a heavier-weight blocking lock.
|
|
|
1422
|
|
|
1423 Thread::SpinAcquire (&_WaitSetLock, "WaitSet - add") ;
|
|
|
1424 AddWaiter (&node) ;
|
|
|
1425 Thread::SpinRelease (&_WaitSetLock) ;
|
|
|
1426
|
|
|
1427 if ((SyncFlags & 4) == 0) {
|
|
|
1428 _Responsible = NULL ;
|
|
|
1429 }
|
|
|
1430 intptr_t save = _recursions; // record the old recursion count
|
|
|
1431 _waiters++; // increment the number of waiters
|
|
|
1432 _recursions = 0; // set the recursion level to be 1
|
|
|
1433 exit (Self) ; // exit the monitor
|
|
|
1434 guarantee (_owner != Self, "invariant") ;
|
|
|
1435
|
|
|
1436 // As soon as the ObjectMonitor's ownership is dropped in the exit()
|
|
|
1437 // call above, another thread can enter() the ObjectMonitor, do the
|
|
|
1438 // notify(), and exit() the ObjectMonitor. If the other thread's
|
|
|
1439 // exit() call chooses this thread as the successor and the unpark()
|
|
|
1440 // call happens to occur while this thread is posting a
|
|
|
1441 // MONITOR_CONTENDED_EXIT event, then we run the risk of the event
|
|
|
1442 // handler using RawMonitors and consuming the unpark().
|
|
|
1443 //
|
|
|
1444 // To avoid the problem, we re-post the event. This does no harm
|
|
|
1445 // even if the original unpark() was not consumed because we are the
|
|
|
1446 // chosen successor for this monitor.
|
|
|
1447 if (node._notified != 0 && _succ == Self) {
|
|
|
1448 node._event->unpark();
|
|
|
1449 }
|
|
|
1450
|
|
|
1451 // The thread is on the WaitSet list - now park() it.
|
|
|
1452 // On MP systems it's conceivable that a brief spin before we park
|
|
|
1453 // could be profitable.
|
|
|
1454 //
|
|
|
1455 // TODO-FIXME: change the following logic to a loop of the form
|
|
|
1456 // while (!timeout && !interrupted && _notified == 0) park()
|
|
|
1457
|
|
|
1458 int ret = OS_OK ;
|
|
|
1459 int WasNotified = 0 ;
|
|
|
1460 { // State transition wrappers
|
|
|
1461 OSThread* osthread = Self->osthread();
|
|
|
1462 OSThreadWaitState osts(osthread, true);
|
|
|
1463 {
|
|
|
1464 ThreadBlockInVM tbivm(jt);
|
|
|
1465 // Thread is in thread_blocked state and oop access is unsafe.
|
|
|
1466 jt->set_suspend_equivalent();
|
|
|
1467
|
|
|
1468 if (interruptible && (Thread::is_interrupted(THREAD, false) || HAS_PENDING_EXCEPTION)) {
|
|
|
1469 // Intentionally empty
|
|
|
1470 } else
|
|
|
1471 if (node._notified == 0) {
|
|
|
1472 if (millis <= 0) {
|
|
|
1473 Self->_ParkEvent->park () ;
|
|
|
1474 } else {
|
|
|
1475 ret = Self->_ParkEvent->park (millis) ;
|
|
|
1476 }
|
|
|
1477 }
|
|
|
1478
|
|
|
1479 // were we externally suspended while we were waiting?
|
|
|
1480 if (ExitSuspendEquivalent (jt)) {
|
|
|
1481 // TODO-FIXME: add -- if succ == Self then succ = null.
|
|
|
1482 jt->java_suspend_self();
|
|
|
1483 }
|
|
|
1484
|
|
|
1485 } // Exit thread safepoint: transition _thread_blocked -> _thread_in_vm
|
|
|
1486
|
|
|
1487
|
|
|
1488 // Node may be on the WaitSet, the EntryList (or cxq), or in transition
|
|
|
1489 // from the WaitSet to the EntryList.
|
|
|
1490 // See if we need to remove Node from the WaitSet.
|
|
|
1491 // We use double-checked locking to avoid grabbing _WaitSetLock
|
|
|
1492 // if the thread is not on the wait queue.
|
|
|
1493 //
|
|
|
1494 // Note that we don't need a fence before the fetch of TState.
|
|
|
1495 // In the worst case we'll fetch a old-stale value of TS_WAIT previously
|
|
|
1496 // written by the is thread. (perhaps the fetch might even be satisfied
|
|
|
1497 // by a look-aside into the processor's own store buffer, although given
|
|
|
1498 // the length of the code path between the prior ST and this load that's
|
|
|
1499 // highly unlikely). If the following LD fetches a stale TS_WAIT value
|
|
|
1500 // then we'll acquire the lock and then re-fetch a fresh TState value.
|
|
|
1501 // That is, we fail toward safety.
|
|
|
1502
|
|
|
1503 if (node.TState == ObjectWaiter::TS_WAIT) {
|
|
|
1504 Thread::SpinAcquire (&_WaitSetLock, "WaitSet - unlink") ;
|
|
|
1505 if (node.TState == ObjectWaiter::TS_WAIT) {
|
|
|
1506 DequeueSpecificWaiter (&node) ; // unlink from WaitSet
|
|
|
1507 assert(node._notified == 0, "invariant");
|
|
|
1508 node.TState = ObjectWaiter::TS_RUN ;
|
|
|
1509 }
|
|
|
1510 Thread::SpinRelease (&_WaitSetLock) ;
|
|
|
1511 }
|
|
|
1512
|
|
|
1513 // The thread is now either on off-list (TS_RUN),
|
|
|
1514 // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
|
|
|
1515 // The Node's TState variable is stable from the perspective of this thread.
|
|
|
1516 // No other threads will asynchronously modify TState.
|
|
|
1517 guarantee (node.TState != ObjectWaiter::TS_WAIT, "invariant") ;
|
|
|
1518 OrderAccess::loadload() ;
|
|
|
1519 if (_succ == Self) _succ = NULL ;
|
|
|
1520 WasNotified = node._notified ;
|
|
|
1521
|
|
|
1522 // Reentry phase -- reacquire the monitor.
|
|
|
1523 // re-enter contended monitor after object.wait().
|
|
|
1524 // retain OBJECT_WAIT state until re-enter successfully completes
|
|
|
1525 // Thread state is thread_in_vm and oop access is again safe,
|
|
|
1526 // although the raw address of the object may have changed.
|
|
|
1527 // (Don't cache naked oops over safepoints, of course).
|
|
|
1528
|
|
|
1529 // post monitor waited event. Note that this is past-tense, we are done waiting.
|
|
|
1530 if (JvmtiExport::should_post_monitor_waited()) {
|
|
|
1531 JvmtiExport::post_monitor_waited(jt, this, ret == OS_TIMEOUT);
|
|
|
1532 }
|
|
|
1533 OrderAccess::fence() ;
|
|
|
1534
|
|
|
1535 assert (Self->_Stalled != 0, "invariant") ;
|
|
|
1536 Self->_Stalled = 0 ;
|
|
|
1537
|
|
|
1538 assert (_owner != Self, "invariant") ;
|
|
|
1539 ObjectWaiter::TStates v = node.TState ;
|
|
|
1540 if (v == ObjectWaiter::TS_RUN) {
|
|
|
1541 enter (Self) ;
|
|
|
1542 } else {
|
|
|
1543 guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
|
|
|
1544 ReenterI (Self, &node) ;
|
|
|
1545 node.wait_reenter_end(this);
|
|
|
1546 }
|
|
|
1547
|
|
|
1548 // Self has reacquired the lock.
|
|
|
1549 // Lifecycle - the node representing Self must not appear on any queues.
|
|
|
1550 // Node is about to go out-of-scope, but even if it were immortal we wouldn't
|
|
|
1551 // want residual elements associated with this thread left on any lists.
|
|
|
1552 guarantee (node.TState == ObjectWaiter::TS_RUN, "invariant") ;
|
|
|
1553 assert (_owner == Self, "invariant") ;
|
|
|
1554 assert (_succ != Self , "invariant") ;
|
|
|
1555 } // OSThreadWaitState()
|
|
|
1556
|
|
|
1557 jt->set_current_waiting_monitor(NULL);
|
|
|
1558
|
|
|
1559 guarantee (_recursions == 0, "invariant") ;
|
|
|
1560 _recursions = save; // restore the old recursion count
|
|
|
1561 _waiters--; // decrement the number of waiters
|
|
|
1562
|
|
|
1563 // Verify a few postconditions
|
|
|
1564 assert (_owner == Self , "invariant") ;
|
|
|
1565 assert (_succ != Self , "invariant") ;
|
|
|
1566 assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
|
|
|
1567
|
|
|
1568 if (SyncFlags & 32) {
|
|
|
1569 OrderAccess::fence() ;
|
|
|
1570 }
|
|
|
1571
|
|
|
1572 // check if the notification happened
|
|
|
1573 if (!WasNotified) {
|
|
|
1574 // no, it could be timeout or Thread.interrupt() or both
|
|
|
1575 // check for interrupt event, otherwise it is timeout
|
|
|
1576 if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
|
|
|
1577 TEVENT (Wait - throw IEX from epilog) ;
|
|
|
1578 THROW(vmSymbols::java_lang_InterruptedException());
|
|
|
1579 }
|
|
|
1580 }
|
|
|
1581
|
|
|
1582 // NOTE: Spurious wake up will be consider as timeout.
|
|
|
1583 // Monitor notify has precedence over thread interrupt.
|
|
|
1584 }
|
|
|
1585
|
|
|
1586
|
|
|
1587 // Consider:
|
|
|
1588 // If the lock is cool (cxq == null && succ == null) and we're on an MP system
|
|
|
1589 // then instead of transferring a thread from the WaitSet to the EntryList
|
|
|
1590 // we might just dequeue a thread from the WaitSet and directly unpark() it.
|
|
|
1591
|
|
|
1592 void ObjectMonitor::notify(TRAPS) {
|
|
|
1593 CHECK_OWNER();
|
|
|
1594 if (_WaitSet == NULL) {
|
|
|
1595 TEVENT (Empty-Notify) ;
|
|
|
1596 return ;
|
|
|
1597 }
|
|
|
1598 DTRACE_MONITOR_PROBE(notify, this, object(), THREAD);
|
|
|
1599
|
|
|
1600 int Policy = Knob_MoveNotifyee ;
|
|
|
1601
|
|
|
1602 Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notify") ;
|
|
|
1603 ObjectWaiter * iterator = DequeueWaiter() ;
|
|
|
1604 if (iterator != NULL) {
|
|
|
1605 TEVENT (Notify1 - Transfer) ;
|
|
|
1606 guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
|
|
|
1607 guarantee (iterator->_notified == 0, "invariant") ;
|
|
|
1608 if (Policy != 4) {
|
|
|
1609 iterator->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1610 }
|
|
|
1611 iterator->_notified = 1 ;
|
|
|
1612
|
|
|
1613 ObjectWaiter * List = _EntryList ;
|
|
|
1614 if (List != NULL) {
|
|
|
1615 assert (List->_prev == NULL, "invariant") ;
|
|
|
1616 assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
1617 assert (List != iterator, "invariant") ;
|
|
|
1618 }
|
|
|
1619
|
|
|
1620 if (Policy == 0) { // prepend to EntryList
|
|
|
1621 if (List == NULL) {
|
|
|
1622 iterator->_next = iterator->_prev = NULL ;
|
|
|
1623 _EntryList = iterator ;
|
|
|
1624 } else {
|
|
|
1625 List->_prev = iterator ;
|
|
|
1626 iterator->_next = List ;
|
|
|
1627 iterator->_prev = NULL ;
|
|
|
1628 _EntryList = iterator ;
|
|
|
1629 }
|
|
|
1630 } else
|
|
|
1631 if (Policy == 1) { // append to EntryList
|
|
|
1632 if (List == NULL) {
|
|
|
1633 iterator->_next = iterator->_prev = NULL ;
|
|
|
1634 _EntryList = iterator ;
|
|
|
1635 } else {
|
|
|
1636 // CONSIDER: finding the tail currently requires a linear-time walk of
|
|
|
1637 // the EntryList. We can make tail access constant-time by converting to
|
|
|
1638 // a CDLL instead of using our current DLL.
|
|
|
1639 ObjectWaiter * Tail ;
|
|
|
1640 for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
|
|
|
1641 assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
|
|
|
1642 Tail->_next = iterator ;
|
|
|
1643 iterator->_prev = Tail ;
|
|
|
1644 iterator->_next = NULL ;
|
|
|
1645 }
|
|
|
1646 } else
|
|
|
1647 if (Policy == 2) { // prepend to cxq
|
|
|
1648 // prepend to cxq
|
|
|
1649 if (List == NULL) {
|
|
|
1650 iterator->_next = iterator->_prev = NULL ;
|
|
|
1651 _EntryList = iterator ;
|
|
|
1652 } else {
|
|
|
1653 iterator->TState = ObjectWaiter::TS_CXQ ;
|
|
|
1654 for (;;) {
|
|
|
1655 ObjectWaiter * Front = _cxq ;
|
|
|
1656 iterator->_next = Front ;
|
|
|
1657 if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
|
|
|
1658 break ;
|
|
|
1659 }
|
|
|
1660 }
|
|
|
1661 }
|
|
|
1662 } else
|
|
|
1663 if (Policy == 3) { // append to cxq
|
|
|
1664 iterator->TState = ObjectWaiter::TS_CXQ ;
|
|
|
1665 for (;;) {
|
|
|
1666 ObjectWaiter * Tail ;
|
|
|
1667 Tail = _cxq ;
|
|
|
1668 if (Tail == NULL) {
|
|
|
1669 iterator->_next = NULL ;
|
|
|
1670 if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
|
|
|
1671 break ;
|
|
|
1672 }
|
|
|
1673 } else {
|
|
|
1674 while (Tail->_next != NULL) Tail = Tail->_next ;
|
|
|
1675 Tail->_next = iterator ;
|
|
|
1676 iterator->_prev = Tail ;
|
|
|
1677 iterator->_next = NULL ;
|
|
|
1678 break ;
|
|
|
1679 }
|
|
|
1680 }
|
|
|
1681 } else {
|
|
|
1682 ParkEvent * ev = iterator->_event ;
|
|
|
1683 iterator->TState = ObjectWaiter::TS_RUN ;
|
|
|
1684 OrderAccess::fence() ;
|
|
|
1685 ev->unpark() ;
|
|
|
1686 }
|
|
|
1687
|
|
|
1688 if (Policy < 4) {
|
|
|
1689 iterator->wait_reenter_begin(this);
|
|
|
1690 }
|
|
|
1691
|
|
|
1692 // _WaitSetLock protects the wait queue, not the EntryList. We could
|
|
|
1693 // move the add-to-EntryList operation, above, outside the critical section
|
|
|
1694 // protected by _WaitSetLock. In practice that's not useful. With the
|
|
|
1695 // exception of wait() timeouts and interrupts the monitor owner
|
|
|
1696 // is the only thread that grabs _WaitSetLock. There's almost no contention
|
|
|
1697 // on _WaitSetLock so it's not profitable to reduce the length of the
|
|
|
1698 // critical section.
|
|
|
1699 }
|
|
|
1700
|
|
|
1701 Thread::SpinRelease (&_WaitSetLock) ;
|
|
|
1702
|
|
|
1703 if (iterator != NULL && ObjectMonitor::_sync_Notifications != NULL) {
|
|
|
1704 ObjectMonitor::_sync_Notifications->inc() ;
|
|
|
1705 }
|
|
|
1706 }
|
|
|
1707
|
|
|
1708
|
|
|
1709 void ObjectMonitor::notifyAll(TRAPS) {
|
|
|
1710 CHECK_OWNER();
|
|
|
1711 ObjectWaiter* iterator;
|
|
|
1712 if (_WaitSet == NULL) {
|
|
|
1713 TEVENT (Empty-NotifyAll) ;
|
|
|
1714 return ;
|
|
|
1715 }
|
|
|
1716 DTRACE_MONITOR_PROBE(notifyAll, this, object(), THREAD);
|
|
|
1717
|
|
|
1718 int Policy = Knob_MoveNotifyee ;
|
|
|
1719 int Tally = 0 ;
|
|
|
1720 Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notifyall") ;
|
|
|
1721
|
|
|
1722 for (;;) {
|
|
|
1723 iterator = DequeueWaiter () ;
|
|
|
1724 if (iterator == NULL) break ;
|
|
|
1725 TEVENT (NotifyAll - Transfer1) ;
|
|
|
1726 ++Tally ;
|
|
|
1727
|
|
|
1728 // Disposition - what might we do with iterator ?
|
|
|
1729 // a. add it directly to the EntryList - either tail or head.
|
|
|
1730 // b. push it onto the front of the _cxq.
|
|
|
1731 // For now we use (a).
|
|
|
1732
|
|
|
1733 guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
|
|
|
1734 guarantee (iterator->_notified == 0, "invariant") ;
|
|
|
1735 iterator->_notified = 1 ;
|
|
|
1736 if (Policy != 4) {
|
|
|
1737 iterator->TState = ObjectWaiter::TS_ENTER ;
|
|
|
1738 }
|
|
|
1739
|
|
|
1740 ObjectWaiter * List = _EntryList ;
|
|
|
1741 if (List != NULL) {
|
|
|
1742 assert (List->_prev == NULL, "invariant") ;
|
|
|
1743 assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
|
|
|
1744 assert (List != iterator, "invariant") ;
|
|
|
1745 }
|
|
|
1746
|
|
|
1747 if (Policy == 0) { // prepend to EntryList
|
|
|
1748 if (List == NULL) {
|
|
|
1749 iterator->_next = iterator->_prev = NULL ;
|
|
|
1750 _EntryList = iterator ;
|
|
|
1751 } else {
|
|
|
1752 List->_prev = iterator ;
|
|
|
1753 iterator->_next = List ;
|
|
|
1754 iterator->_prev = NULL ;
|
|
|
1755 _EntryList = iterator ;
|
|
|
1756 }
|
|
|
1757 } else
|
|
|
1758 if (Policy == 1) { // append to EntryList
|
|
|
1759 if (List == NULL) {
|
|
|
1760 iterator->_next = iterator->_prev = NULL ;
|
|
|
1761 _EntryList = iterator ;
|
|
|
1762 } else {
|
|
|
1763 // CONSIDER: finding the tail currently requires a linear-time walk of
|
|
|
1764 // the EntryList. We can make tail access constant-time by converting to
|
|
|
1765 // a CDLL instead of using our current DLL.
|
|
|
1766 ObjectWaiter * Tail ;
|
|
|
1767 for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
|
|
|
1768 assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
|
|
|
1769 Tail->_next = iterator ;
|
|
|
1770 iterator->_prev = Tail ;
|
|
|
1771 iterator->_next = NULL ;
|
|
|
1772 }
|
|
|
1773 } else
|
|
|
1774 if (Policy == 2) { // prepend to cxq
|
|
|
1775 // prepend to cxq
|
|
|
1776 iterator->TState = ObjectWaiter::TS_CXQ ;
|
|
|
1777 for (;;) {
|
|
|
1778 ObjectWaiter * Front = _cxq ;
|
|
|
1779 iterator->_next = Front ;
|
|
|
1780 if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
|
|
|
1781 break ;
|
|
|
1782 }
|
|
|
1783 }
|
|
|
1784 } else
|
|
|
1785 if (Policy == 3) { // append to cxq
|
|
|
1786 iterator->TState = ObjectWaiter::TS_CXQ ;
|
|
|
1787 for (;;) {
|
|
|
1788 ObjectWaiter * Tail ;
|
|
|
1789 Tail = _cxq ;
|
|
|
1790 if (Tail == NULL) {
|
|
|
1791 iterator->_next = NULL ;
|
|
|
1792 if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
|
|
|
1793 break ;
|
|
|
1794 }
|
|
|
1795 } else {
|
|
|
1796 while (Tail->_next != NULL) Tail = Tail->_next ;
|
|
|
1797 Tail->_next = iterator ;
|
|
|
1798 iterator->_prev = Tail ;
|
|
|
1799 iterator->_next = NULL ;
|
|
|
1800 break ;
|
|
|
1801 }
|
|
|
1802 }
|
|
|
1803 } else {
|
|
|
1804 ParkEvent * ev = iterator->_event ;
|
|
|
1805 iterator->TState = ObjectWaiter::TS_RUN ;
|
|
|
1806 OrderAccess::fence() ;
|
|
|
1807 ev->unpark() ;
|
|
|
1808 }
|
|
|
1809
|
|
|
1810 if (Policy < 4) {
|
|
|
1811 iterator->wait_reenter_begin(this);
|
|
|
1812 }
|
|
|
1813
|
|
|
1814 // _WaitSetLock protects the wait queue, not the EntryList. We could
|
|
|
1815 // move the add-to-EntryList operation, above, outside the critical section
|
|
|
1816 // protected by _WaitSetLock. In practice that's not useful. With the
|
|
|
1817 // exception of wait() timeouts and interrupts the monitor owner
|
|
|
1818 // is the only thread that grabs _WaitSetLock. There's almost no contention
|
|
|
1819 // on _WaitSetLock so it's not profitable to reduce the length of the
|
|
|
1820 // critical section.
|
|
|
1821 }
|
|
|
1822
|
|
|
1823 Thread::SpinRelease (&_WaitSetLock) ;
|
|
|
1824
|
|
|
1825 if (Tally != 0 && ObjectMonitor::_sync_Notifications != NULL) {
|
|
|
1826 ObjectMonitor::_sync_Notifications->inc(Tally) ;
|
|
|
1827 }
|
|
|
1828 }
|
|
|
1829
|
|
|
1830 // -----------------------------------------------------------------------------
|
|
|
1831 // Adaptive Spinning Support
|
|
|
1832 //
|
|
|
1833 // Adaptive spin-then-block - rational spinning
|
|
|
1834 //
|
|
|
1835 // Note that we spin "globally" on _owner with a classic SMP-polite TATAS
|
|
|
1836 // algorithm. On high order SMP systems it would be better to start with
|
|
|
1837 // a brief global spin and then revert to spinning locally. In the spirit of MCS/CLH,
|
|
|
1838 // a contending thread could enqueue itself on the cxq and then spin locally
|
|
|
1839 // on a thread-specific variable such as its ParkEvent._Event flag.
|
|
|
1840 // That's left as an exercise for the reader. Note that global spinning is
|
|
|
1841 // not problematic on Niagara, as the L2$ serves the interconnect and has both
|
|
|
1842 // low latency and massive bandwidth.
|
|
|
1843 //
|
|
|
1844 // Broadly, we can fix the spin frequency -- that is, the % of contended lock
|
|
|
1845 // acquisition attempts where we opt to spin -- at 100% and vary the spin count
|
|
|
1846 // (duration) or we can fix the count at approximately the duration of
|
|
|
1847 // a context switch and vary the frequency. Of course we could also
|
|
|
1848 // vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
|
|
|
1849 // See http://j2se.east/~dice/PERSIST/040824-AdaptiveSpinning.html.
|
|
|
1850 //
|
|
|
1851 // This implementation varies the duration "D", where D varies with
|
|
|
1852 // the success rate of recent spin attempts. (D is capped at approximately
|
|
|
1853 // length of a round-trip context switch). The success rate for recent
|
|
|
1854 // spin attempts is a good predictor of the success rate of future spin
|
|
|
1855 // attempts. The mechanism adapts automatically to varying critical
|
|
|
1856 // section length (lock modality), system load and degree of parallelism.
|
|
|
1857 // D is maintained per-monitor in _SpinDuration and is initialized
|
|
|
1858 // optimistically. Spin frequency is fixed at 100%.
|
|
|
1859 //
|
|
|
1860 // Note that _SpinDuration is volatile, but we update it without locks
|
|
|
1861 // or atomics. The code is designed so that _SpinDuration stays within
|
|
|
1862 // a reasonable range even in the presence of races. The arithmetic
|
|
|
1863 // operations on _SpinDuration are closed over the domain of legal values,
|
|
|
1864 // so at worst a race will install and older but still legal value.
|
|
|
1865 // At the very worst this introduces some apparent non-determinism.
|
|
|
1866 // We might spin when we shouldn't or vice-versa, but since the spin
|
|
|
1867 // count are relatively short, even in the worst case, the effect is harmless.
|
|
|
1868 //
|
|
|
1869 // Care must be taken that a low "D" value does not become an
|
|
|
1870 // an absorbing state. Transient spinning failures -- when spinning
|
|
|
1871 // is overall profitable -- should not cause the system to converge
|
|
|
1872 // on low "D" values. We want spinning to be stable and predictable
|
|
|
1873 // and fairly responsive to change and at the same time we don't want
|
|
|
1874 // it to oscillate, become metastable, be "too" non-deterministic,
|
|
|
1875 // or converge on or enter undesirable stable absorbing states.
|
|
|
1876 //
|
|
|
1877 // We implement a feedback-based control system -- using past behavior
|
|
|
1878 // to predict future behavior. We face two issues: (a) if the
|
|
|
1879 // input signal is random then the spin predictor won't provide optimal
|
|
|
1880 // results, and (b) if the signal frequency is too high then the control
|
|
|
1881 // system, which has some natural response lag, will "chase" the signal.
|
|
|
1882 // (b) can arise from multimodal lock hold times. Transient preemption
|
|
|
1883 // can also result in apparent bimodal lock hold times.
|
|
|
1884 // Although sub-optimal, neither condition is particularly harmful, as
|
|
|
1885 // in the worst-case we'll spin when we shouldn't or vice-versa.
|
|
|
1886 // The maximum spin duration is rather short so the failure modes aren't bad.
|
|
|
1887 // To be conservative, I've tuned the gain in system to bias toward
|
|
|
1888 // _not spinning. Relatedly, the system can sometimes enter a mode where it
|
|
|
1889 // "rings" or oscillates between spinning and not spinning. This happens
|
|
|
1890 // when spinning is just on the cusp of profitability, however, so the
|
|
|
1891 // situation is not dire. The state is benign -- there's no need to add
|
|
|
1892 // hysteresis control to damp the transition rate between spinning and
|
|
|
1893 // not spinning.
|
|
|
1894 //
|
|
|
1895
|
|
|
1896 intptr_t ObjectMonitor::SpinCallbackArgument = 0 ;
|
|
|
1897 int (*ObjectMonitor::SpinCallbackFunction)(intptr_t, int) = NULL ;
|
|
|
1898
|
|
|
1899 // Spinning: Fixed frequency (100%), vary duration
|
|
|
1900
|
|
|
1901
|
|
|
1902 int ObjectMonitor::TrySpin_VaryDuration (Thread * Self) {
|
|
|
1903
|
|
|
1904 // Dumb, brutal spin. Good for comparative measurements against adaptive spinning.
|
|
|
1905 int ctr = Knob_FixedSpin ;
|
|
|
1906 if (ctr != 0) {
|
|
|
1907 while (--ctr >= 0) {
|
|
|
1908 if (TryLock (Self) > 0) return 1 ;
|
|
|
1909 SpinPause () ;
|
|
|
1910 }
|
|
|
1911 return 0 ;
|
|
|
1912 }
|
|
|
1913
|
|
|
1914 for (ctr = Knob_PreSpin + 1; --ctr >= 0 ; ) {
|
|
|
1915 if (TryLock(Self) > 0) {
|
|
|
1916 // Increase _SpinDuration ...
|
|
|
1917 // Note that we don't clamp SpinDuration precisely at SpinLimit.
|
|
|
1918 // Raising _SpurDuration to the poverty line is key.
|
|
|
1919 int x = _SpinDuration ;
|
|
|
1920 if (x < Knob_SpinLimit) {
|
|
|
1921 if (x < Knob_Poverty) x = Knob_Poverty ;
|
|
|
1922 _SpinDuration = x + Knob_BonusB ;
|
|
|
1923 }
|
|
|
1924 return 1 ;
|
|
|
1925 }
|
|
|
1926 SpinPause () ;
|
|
|
1927 }
|
|
|
1928
|
|
|
1929 // Admission control - verify preconditions for spinning
|
|
|
1930 //
|
|
|
1931 // We always spin a little bit, just to prevent _SpinDuration == 0 from
|
|
|
1932 // becoming an absorbing state. Put another way, we spin briefly to
|
|
|
1933 // sample, just in case the system load, parallelism, contention, or lock
|
|
|
1934 // modality changed.
|
|
|
1935 //
|
|
|
1936 // Consider the following alternative:
|
|
|
1937 // Periodically set _SpinDuration = _SpinLimit and try a long/full
|
|
|
1938 // spin attempt. "Periodically" might mean after a tally of
|
|
|
1939 // the # of failed spin attempts (or iterations) reaches some threshold.
|
|
|
1940 // This takes us into the realm of 1-out-of-N spinning, where we
|
|
|
1941 // hold the duration constant but vary the frequency.
|
|
|
1942
|
|
|
1943 ctr = _SpinDuration ;
|
|
|
1944 if (ctr < Knob_SpinBase) ctr = Knob_SpinBase ;
|
|
|
1945 if (ctr <= 0) return 0 ;
|
|
|
1946
|
|
|
1947 if (Knob_SuccRestrict && _succ != NULL) return 0 ;
|
|
|
1948 if (Knob_OState && NotRunnable (Self, (Thread *) _owner)) {
|
|
|
1949 TEVENT (Spin abort - notrunnable [TOP]);
|
|
|
1950 return 0 ;
|
|
|
1951 }
|
|
|
1952
|
|
|
1953 int MaxSpin = Knob_MaxSpinners ;
|
|
|
1954 if (MaxSpin >= 0) {
|
|
|
1955 if (_Spinner > MaxSpin) {
|
|
|
1956 TEVENT (Spin abort -- too many spinners) ;
|
|
|
1957 return 0 ;
|
|
|
1958 }
|
|
|
1959 // Slighty racy, but benign ...
|
|
|
1960 Adjust (&_Spinner, 1) ;
|
|
|
1961 }
|
|
|
1962
|
|
|
1963 // We're good to spin ... spin ingress.
|
|
|
1964 // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
|
|
|
1965 // when preparing to LD...CAS _owner, etc and the CAS is likely
|
|
|
1966 // to succeed.
|
|
|
1967 int hits = 0 ;
|
|
|
1968 int msk = 0 ;
|
|
|
1969 int caspty = Knob_CASPenalty ;
|
|
|
1970 int oxpty = Knob_OXPenalty ;
|
|
|
1971 int sss = Knob_SpinSetSucc ;
|
|
|
1972 if (sss && _succ == NULL ) _succ = Self ;
|
|
|
1973 Thread * prv = NULL ;
|
|
|
1974
|
|
|
1975 // There are three ways to exit the following loop:
|
|
|
1976 // 1. A successful spin where this thread has acquired the lock.
|
|
|
1977 // 2. Spin failure with prejudice
|
|
|
1978 // 3. Spin failure without prejudice
|
|
|
1979
|
|
|
1980 while (--ctr >= 0) {
|
|
|
1981
|
|
|
1982 // Periodic polling -- Check for pending GC
|
|
|
1983 // Threads may spin while they're unsafe.
|
|
|
1984 // We don't want spinning threads to delay the JVM from reaching
|
|
|
1985 // a stop-the-world safepoint or to steal cycles from GC.
|
|
|
1986 // If we detect a pending safepoint we abort in order that
|
|
|
1987 // (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
|
|
|
1988 // this thread, if safe, doesn't steal cycles from GC.
|
|
|
1989 // This is in keeping with the "no loitering in runtime" rule.
|
|
|
1990 // We periodically check to see if there's a safepoint pending.
|
|
|
1991 if ((ctr & 0xFF) == 0) {
|
|
|
1992 if (SafepointSynchronize::do_call_back()) {
|
|
|
1993 TEVENT (Spin: safepoint) ;
|
|
|
1994 goto Abort ; // abrupt spin egress
|
|
|
1995 }
|
|
|
1996 if (Knob_UsePause & 1) SpinPause () ;
|
|
|
1997
|
|
|
1998 int (*scb)(intptr_t,int) = SpinCallbackFunction ;
|
|
|
1999 if (hits > 50 && scb != NULL) {
|
|
|
2000 int abend = (*scb)(SpinCallbackArgument, 0) ;
|
|
|
2001 }
|
|
|
2002 }
|
|
|
2003
|
|
|
2004 if (Knob_UsePause & 2) SpinPause() ;
|
|
|
2005
|
|
|
2006 // Exponential back-off ... Stay off the bus to reduce coherency traffic.
|
|
|
2007 // This is useful on classic SMP systems, but is of less utility on
|
|
|
2008 // N1-style CMT platforms.
|
|
|
2009 //
|
|
|
2010 // Trade-off: lock acquisition latency vs coherency bandwidth.
|
|
|
2011 // Lock hold times are typically short. A histogram
|
|
|
2012 // of successful spin attempts shows that we usually acquire
|
|
|
2013 // the lock early in the spin. That suggests we want to
|
|
|
2014 // sample _owner frequently in the early phase of the spin,
|
|
|
2015 // but then back-off and sample less frequently as the spin
|
|
|
2016 // progresses. The back-off makes a good citizen on SMP big
|
|
|
2017 // SMP systems. Oversampling _owner can consume excessive
|
|
|
2018 // coherency bandwidth. Relatedly, if we _oversample _owner we
|
|
|
2019 // can inadvertently interfere with the the ST m->owner=null.
|
|
|
2020 // executed by the lock owner.
|
|
|
2021 if (ctr & msk) continue ;
|
|
|
2022 ++hits ;
|
|
|
2023 if ((hits & 0xF) == 0) {
|
|
|
2024 // The 0xF, above, corresponds to the exponent.
|
|
|
2025 // Consider: (msk+1)|msk
|
|
|
2026 msk = ((msk << 2)|3) & BackOffMask ;
|
|
|
2027 }
|
|
|
2028
|
|
|
2029 // Probe _owner with TATAS
|
|
|
2030 // If this thread observes the monitor transition or flicker
|
|
|
2031 // from locked to unlocked to locked, then the odds that this
|
|
|
2032 // thread will acquire the lock in this spin attempt go down
|
|
|
2033 // considerably. The same argument applies if the CAS fails
|
|
|
2034 // or if we observe _owner change from one non-null value to
|
|
|
2035 // another non-null value. In such cases we might abort
|
|
|
2036 // the spin without prejudice or apply a "penalty" to the
|
|
|
2037 // spin count-down variable "ctr", reducing it by 100, say.
|
|
|
2038
|
|
|
2039 Thread * ox = (Thread *) _owner ;
|
|
|
2040 if (ox == NULL) {
|
|
|
2041 ox = (Thread *) Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
|
|
|
2042 if (ox == NULL) {
|
|
|
2043 // The CAS succeeded -- this thread acquired ownership
|
|
|
2044 // Take care of some bookkeeping to exit spin state.
|
|
|
2045 if (sss && _succ == Self) {
|
|
|
2046 _succ = NULL ;
|
|
|
2047 }
|
|
|
2048 if (MaxSpin > 0) Adjust (&_Spinner, -1) ;
|
|
|
2049
|
|
|
2050 // Increase _SpinDuration :
|
|
|
2051 // The spin was successful (profitable) so we tend toward
|
|
|
2052 // longer spin attempts in the future.
|
|
|
2053 // CONSIDER: factor "ctr" into the _SpinDuration adjustment.
|
|
|
2054 // If we acquired the lock early in the spin cycle it
|
|
|
2055 // makes sense to increase _SpinDuration proportionally.
|
|
|
2056 // Note that we don't clamp SpinDuration precisely at SpinLimit.
|
|
|
2057 int x = _SpinDuration ;
|
|
|
2058 if (x < Knob_SpinLimit) {
|
|
|
2059 if (x < Knob_Poverty) x = Knob_Poverty ;
|
|
|
2060 _SpinDuration = x + Knob_Bonus ;
|
|
|
2061 }
|
|
|
2062 return 1 ;
|
|
|
2063 }
|
|
|
2064
|
|
|
2065 // The CAS failed ... we can take any of the following actions:
|
|
|
2066 // * penalize: ctr -= Knob_CASPenalty
|
|
|
2067 // * exit spin with prejudice -- goto Abort;
|
|
|
2068 // * exit spin without prejudice.
|
|
|
2069 // * Since CAS is high-latency, retry again immediately.
|
|
|
2070 prv = ox ;
|
|
|
2071 TEVENT (Spin: cas failed) ;
|
|
|
2072 if (caspty == -2) break ;
|
|
|
2073 if (caspty == -1) goto Abort ;
|
|
|
2074 ctr -= caspty ;
|
|
|
2075 continue ;
|
|
|
2076 }
|
|
|
2077
|
|
|
2078 // Did lock ownership change hands ?
|
|
|
2079 if (ox != prv && prv != NULL ) {
|
|
|
2080 TEVENT (spin: Owner changed)
|
|
|
2081 if (oxpty == -2) break ;
|
|
|
2082 if (oxpty == -1) goto Abort ;
|
|
|
2083 ctr -= oxpty ;
|
|
|
2084 }
|
|
|
2085 prv = ox ;
|
|
|
2086
|
|
|
2087 // Abort the spin if the owner is not executing.
|
|
|
2088 // The owner must be executing in order to drop the lock.
|
|
|
2089 // Spinning while the owner is OFFPROC is idiocy.
|
|
|
2090 // Consider: ctr -= RunnablePenalty ;
|
|
|
2091 if (Knob_OState && NotRunnable (Self, ox)) {
|
|
|
2092 TEVENT (Spin abort - notrunnable);
|
|
|
2093 goto Abort ;
|
|
|
2094 }
|
|
|
2095 if (sss && _succ == NULL ) _succ = Self ;
|
|
|
2096 }
|
|
|
2097
|
|
|
2098 // Spin failed with prejudice -- reduce _SpinDuration.
|
|
|
2099 // TODO: Use an AIMD-like policy to adjust _SpinDuration.
|
|
|
2100 // AIMD is globally stable.
|
|
|
2101 TEVENT (Spin failure) ;
|
|
|
2102 {
|
|
|
2103 int x = _SpinDuration ;
|
|
|
2104 if (x > 0) {
|
|
|
2105 // Consider an AIMD scheme like: x -= (x >> 3) + 100
|
|
|
2106 // This is globally sample and tends to damp the response.
|
|
|
2107 x -= Knob_Penalty ;
|
|
|
2108 if (x < 0) x = 0 ;
|
|
|
2109 _SpinDuration = x ;
|
|
|
2110 }
|
|
|
2111 }
|
|
|
2112
|
|
|
2113 Abort:
|
|
|
2114 if (MaxSpin >= 0) Adjust (&_Spinner, -1) ;
|
|
|
2115 if (sss && _succ == Self) {
|
|
|
2116 _succ = NULL ;
|
|
|
2117 // Invariant: after setting succ=null a contending thread
|
|
|
2118 // must recheck-retry _owner before parking. This usually happens
|
|
|
2119 // in the normal usage of TrySpin(), but it's safest
|
|
|
2120 // to make TrySpin() as foolproof as possible.
|
|
|
2121 OrderAccess::fence() ;
|
|
|
2122 if (TryLock(Self) > 0) return 1 ;
|
|
|
2123 }
|
|
|
2124 return 0 ;
|
|
|
2125 }
|
|
|
2126
|
|
|
2127 // NotRunnable() -- informed spinning
|
|
|
2128 //
|
|
|
2129 // Don't bother spinning if the owner is not eligible to drop the lock.
|
|
|
2130 // Peek at the owner's schedctl.sc_state and Thread._thread_values and
|
|
|
2131 // spin only if the owner thread is _thread_in_Java or _thread_in_vm.
|
|
|
2132 // The thread must be runnable in order to drop the lock in timely fashion.
|
|
|
2133 // If the _owner is not runnable then spinning will not likely be
|
|
|
2134 // successful (profitable).
|
|
|
2135 //
|
|
|
2136 // Beware -- the thread referenced by _owner could have died
|
|
|
2137 // so a simply fetch from _owner->_thread_state might trap.
|
|
|
2138 // Instead, we use SafeFetchXX() to safely LD _owner->_thread_state.
|
|
|
2139 // Because of the lifecycle issues the schedctl and _thread_state values
|
|
|
2140 // observed by NotRunnable() might be garbage. NotRunnable must
|
|
|
2141 // tolerate this and consider the observed _thread_state value
|
|
|
2142 // as advisory.
|
|
|
2143 //
|
|
|
2144 // Beware too, that _owner is sometimes a BasicLock address and sometimes
|
|
|
2145 // a thread pointer. We differentiate the two cases with OwnerIsThread.
|
|
|
2146 // Alternately, we might tag the type (thread pointer vs basiclock pointer)
|
|
|
2147 // with the LSB of _owner. Another option would be to probablistically probe
|
|
|
2148 // the putative _owner->TypeTag value.
|
|
|
2149 //
|
|
|
2150 // Checking _thread_state isn't perfect. Even if the thread is
|
|
|
2151 // in_java it might be blocked on a page-fault or have been preempted
|
|
|
2152 // and sitting on a ready/dispatch queue. _thread state in conjunction
|
|
|
2153 // with schedctl.sc_state gives us a good picture of what the
|
|
|
2154 // thread is doing, however.
|
|
|
2155 //
|
|
|
2156 // TODO: check schedctl.sc_state.
|
|
|
2157 // We'll need to use SafeFetch32() to read from the schedctl block.
|
|
|
2158 // See RFE #5004247 and http://sac.sfbay.sun.com/Archives/CaseLog/arc/PSARC/2005/351/
|
|
|
2159 //
|
|
|
2160 // The return value from NotRunnable() is *advisory* -- the
|
|
|
2161 // result is based on sampling and is not necessarily coherent.
|
|
|
2162 // The caller must tolerate false-negative and false-positive errors.
|
|
|
2163 // Spinning, in general, is probabilistic anyway.
|
|
|
2164
|
|
|
2165
|
|
|
2166 int ObjectMonitor::NotRunnable (Thread * Self, Thread * ox) {
|
|
|
2167 // Check either OwnerIsThread or ox->TypeTag == 2BAD.
|
|
|
2168 if (!OwnerIsThread) return 0 ;
|
|
|
2169
|
|
|
2170 if (ox == NULL) return 0 ;
|
|
|
2171
|
|
|
2172 // Avoid transitive spinning ...
|
|
|
2173 // Say T1 spins or blocks trying to acquire L. T1._Stalled is set to L.
|
|
|
2174 // Immediately after T1 acquires L it's possible that T2, also
|
|
|
2175 // spinning on L, will see L.Owner=T1 and T1._Stalled=L.
|
|
|
2176 // This occurs transiently after T1 acquired L but before
|
|
|
2177 // T1 managed to clear T1.Stalled. T2 does not need to abort
|
|
|
2178 // its spin in this circumstance.
|
|
|
2179 intptr_t BlockedOn = SafeFetchN ((intptr_t *) &ox->_Stalled, intptr_t(1)) ;
|
|
|
2180
|
|
|
2181 if (BlockedOn == 1) return 1 ;
|
|
|
2182 if (BlockedOn != 0) {
|
|
|
2183 return BlockedOn != intptr_t(this) && _owner == ox ;
|
|
|
2184 }
|
|
|
2185
|
|
|
2186 assert (sizeof(((JavaThread *)ox)->_thread_state == sizeof(int)), "invariant") ;
|
|
|
2187 int jst = SafeFetch32 ((int *) &((JavaThread *) ox)->_thread_state, -1) ; ;
|
|
|
2188 // consider also: jst != _thread_in_Java -- but that's overspecific.
|
|
|
2189 return jst == _thread_blocked || jst == _thread_in_native ;
|
|
|
2190 }
|
|
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2191
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|
2192
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|
|
2193 // -----------------------------------------------------------------------------
|
|
|
2194 // WaitSet management ...
|
|
|
2195
|
|
|
2196 ObjectWaiter::ObjectWaiter(Thread* thread) {
|
|
|
2197 _next = NULL;
|
|
|
2198 _prev = NULL;
|
|
|
2199 _notified = 0;
|
|
|
2200 TState = TS_RUN ;
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|
|
2201 _thread = thread;
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|
|
2202 _event = thread->_ParkEvent ;
|
|
|
2203 _active = false;
|
|
|
2204 assert (_event != NULL, "invariant") ;
|
|
|
2205 }
|
|
|
2206
|
|
|
2207 void ObjectWaiter::wait_reenter_begin(ObjectMonitor *mon) {
|
|
|
2208 JavaThread *jt = (JavaThread *)this->_thread;
|
|
|
2209 _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(jt, mon);
|
|
|
2210 }
|
|
|
2211
|
|
|
2212 void ObjectWaiter::wait_reenter_end(ObjectMonitor *mon) {
|
|
|
2213 JavaThread *jt = (JavaThread *)this->_thread;
|
|
|
2214 JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(jt, _active);
|
|
|
2215 }
|
|
|
2216
|
|
|
2217 inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
|
|
|
2218 assert(node != NULL, "should not dequeue NULL node");
|
|
|
2219 assert(node->_prev == NULL, "node already in list");
|
|
|
2220 assert(node->_next == NULL, "node already in list");
|
|
|
2221 // put node at end of queue (circular doubly linked list)
|
|
|
2222 if (_WaitSet == NULL) {
|
|
|
2223 _WaitSet = node;
|
|
|
2224 node->_prev = node;
|
|
|
2225 node->_next = node;
|
|
|
2226 } else {
|
|
|
2227 ObjectWaiter* head = _WaitSet ;
|
|
|
2228 ObjectWaiter* tail = head->_prev;
|
|
|
2229 assert(tail->_next == head, "invariant check");
|
|
|
2230 tail->_next = node;
|
|
|
2231 head->_prev = node;
|
|
|
2232 node->_next = head;
|
|
|
2233 node->_prev = tail;
|
|
|
2234 }
|
|
|
2235 }
|
|
|
2236
|
|
|
2237 inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
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|
|
2238 // dequeue the very first waiter
|
|
|
2239 ObjectWaiter* waiter = _WaitSet;
|
|
|
2240 if (waiter) {
|
|
|
2241 DequeueSpecificWaiter(waiter);
|
|
|
2242 }
|
|
|
2243 return waiter;
|
|
|
2244 }
|
|
|
2245
|
|
|
2246 inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
|
|
|
2247 assert(node != NULL, "should not dequeue NULL node");
|
|
|
2248 assert(node->_prev != NULL, "node already removed from list");
|
|
|
2249 assert(node->_next != NULL, "node already removed from list");
|
|
|
2250 // when the waiter has woken up because of interrupt,
|
|
|
2251 // timeout or other spurious wake-up, dequeue the
|
|
|
2252 // waiter from waiting list
|
|
|
2253 ObjectWaiter* next = node->_next;
|
|
|
2254 if (next == node) {
|
|
|
2255 assert(node->_prev == node, "invariant check");
|
|
|
2256 _WaitSet = NULL;
|
|
|
2257 } else {
|
|
|
2258 ObjectWaiter* prev = node->_prev;
|
|
|
2259 assert(prev->_next == node, "invariant check");
|
|
|
2260 assert(next->_prev == node, "invariant check");
|
|
|
2261 next->_prev = prev;
|
|
|
2262 prev->_next = next;
|
|
|
2263 if (_WaitSet == node) {
|
|
|
2264 _WaitSet = next;
|
|
|
2265 }
|
|
|
2266 }
|
|
|
2267 node->_next = NULL;
|
|
|
2268 node->_prev = NULL;
|
|
|
2269 }
|
|
|
2270
|
|
|
2271 // -----------------------------------------------------------------------------
|
|
|
2272 // PerfData support
|
|
|
2273 PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts = NULL ;
|
|
|
2274 PerfCounter * ObjectMonitor::_sync_FutileWakeups = NULL ;
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|
|
2275 PerfCounter * ObjectMonitor::_sync_Parks = NULL ;
|
|
|
2276 PerfCounter * ObjectMonitor::_sync_EmptyNotifications = NULL ;
|
|
|
2277 PerfCounter * ObjectMonitor::_sync_Notifications = NULL ;
|
|
|
2278 PerfCounter * ObjectMonitor::_sync_PrivateA = NULL ;
|
|
|
2279 PerfCounter * ObjectMonitor::_sync_PrivateB = NULL ;
|
|
|
2280 PerfCounter * ObjectMonitor::_sync_SlowExit = NULL ;
|
|
|
2281 PerfCounter * ObjectMonitor::_sync_SlowEnter = NULL ;
|
|
|
2282 PerfCounter * ObjectMonitor::_sync_SlowNotify = NULL ;
|
|
|
2283 PerfCounter * ObjectMonitor::_sync_SlowNotifyAll = NULL ;
|
|
|
2284 PerfCounter * ObjectMonitor::_sync_FailedSpins = NULL ;
|
|
|
2285 PerfCounter * ObjectMonitor::_sync_SuccessfulSpins = NULL ;
|
|
|
2286 PerfCounter * ObjectMonitor::_sync_MonInCirculation = NULL ;
|
|
|
2287 PerfCounter * ObjectMonitor::_sync_MonScavenged = NULL ;
|
|
|
2288 PerfCounter * ObjectMonitor::_sync_Inflations = NULL ;
|
|
|
2289 PerfCounter * ObjectMonitor::_sync_Deflations = NULL ;
|
|
|
2290 PerfLongVariable * ObjectMonitor::_sync_MonExtant = NULL ;
|
|
|
2291
|
|
|
2292 // One-shot global initialization for the sync subsystem.
|
|
|
2293 // We could also defer initialization and initialize on-demand
|
|
|
2294 // the first time we call inflate(). Initialization would
|
|
|
2295 // be protected - like so many things - by the MonitorCache_lock.
|
|
|
2296
|
|
|
2297 void ObjectMonitor::Initialize () {
|
|
|
2298 static int InitializationCompleted = 0 ;
|
|
|
2299 assert (InitializationCompleted == 0, "invariant") ;
|
|
|
2300 InitializationCompleted = 1 ;
|
|
|
2301 if (UsePerfData) {
|
|
|
2302 EXCEPTION_MARK ;
|
|
|
2303 #define NEWPERFCOUNTER(n) {n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,CHECK); }
|
|
|
2304 #define NEWPERFVARIABLE(n) {n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,CHECK); }
|
|
|
2305 NEWPERFCOUNTER(_sync_Inflations) ;
|
|
|
2306 NEWPERFCOUNTER(_sync_Deflations) ;
|
|
|
2307 NEWPERFCOUNTER(_sync_ContendedLockAttempts) ;
|
|
|
2308 NEWPERFCOUNTER(_sync_FutileWakeups) ;
|
|
|
2309 NEWPERFCOUNTER(_sync_Parks) ;
|
|
|
2310 NEWPERFCOUNTER(_sync_EmptyNotifications) ;
|
|
|
2311 NEWPERFCOUNTER(_sync_Notifications) ;
|
|
|
2312 NEWPERFCOUNTER(_sync_SlowEnter) ;
|
|
|
2313 NEWPERFCOUNTER(_sync_SlowExit) ;
|
|
|
2314 NEWPERFCOUNTER(_sync_SlowNotify) ;
|
|
|
2315 NEWPERFCOUNTER(_sync_SlowNotifyAll) ;
|
|
|
2316 NEWPERFCOUNTER(_sync_FailedSpins) ;
|
|
|
2317 NEWPERFCOUNTER(_sync_SuccessfulSpins) ;
|
|
|
2318 NEWPERFCOUNTER(_sync_PrivateA) ;
|
|
|
2319 NEWPERFCOUNTER(_sync_PrivateB) ;
|
|
|
2320 NEWPERFCOUNTER(_sync_MonInCirculation) ;
|
|
|
2321 NEWPERFCOUNTER(_sync_MonScavenged) ;
|
|
|
2322 NEWPERFVARIABLE(_sync_MonExtant) ;
|
|
|
2323 #undef NEWPERFCOUNTER
|
|
|
2324 }
|
|
|
2325 }
|
|
|
2326
|
|
|
2327
|
|
|
2328 // Compile-time asserts
|
|
|
2329 // When possible, it's better to catch errors deterministically at
|
|
|
2330 // compile-time than at runtime. The down-side to using compile-time
|
|
|
2331 // asserts is that error message -- often something about negative array
|
|
|
2332 // indices -- is opaque.
|
|
|
2333
|
|
|
2334 #define CTASSERT(x) { int tag[1-(2*!(x))]; printf ("Tag @" INTPTR_FORMAT "\n", (intptr_t)tag); }
|
|
|
2335
|
|
|
2336 void ObjectMonitor::ctAsserts() {
|
|
|
2337 CTASSERT(offset_of (ObjectMonitor, _header) == 0);
|
|
|
2338 }
|
|
|
2339
|
|
|
2340
|
|
|
2341 static char * kvGet (char * kvList, const char * Key) {
|
|
|
2342 if (kvList == NULL) return NULL ;
|
|
|
2343 size_t n = strlen (Key) ;
|
|
|
2344 char * Search ;
|
|
|
2345 for (Search = kvList ; *Search ; Search += strlen(Search) + 1) {
|
|
|
2346 if (strncmp (Search, Key, n) == 0) {
|
|
|
2347 if (Search[n] == '=') return Search + n + 1 ;
|
|
|
2348 if (Search[n] == 0) return (char *) "1" ;
|
|
|
2349 }
|
|
|
2350 }
|
|
|
2351 return NULL ;
|
|
|
2352 }
|
|
|
2353
|
|
|
2354 static int kvGetInt (char * kvList, const char * Key, int Default) {
|
|
|
2355 char * v = kvGet (kvList, Key) ;
|
|
|
2356 int rslt = v ? ::strtol (v, NULL, 0) : Default ;
|
|
|
2357 if (Knob_ReportSettings && v != NULL) {
|
|
|
2358 ::printf (" SyncKnob: %s %d(%d)\n", Key, rslt, Default) ;
|
|
|
2359 ::fflush (stdout) ;
|
|
|
2360 }
|
|
|
2361 return rslt ;
|
|
|
2362 }
|
|
|
2363
|
|
|
2364 void ObjectMonitor::DeferredInitialize () {
|
|
|
2365 if (InitDone > 0) return ;
|
|
|
2366 if (Atomic::cmpxchg (-1, &InitDone, 0) != 0) {
|
|
|
2367 while (InitDone != 1) ;
|
|
|
2368 return ;
|
|
|
2369 }
|
|
|
2370
|
|
|
2371 // One-shot global initialization ...
|
|
|
2372 // The initialization is idempotent, so we don't need locks.
|
|
|
2373 // In the future consider doing this via os::init_2().
|
|
|
2374 // SyncKnobs consist of <Key>=<Value> pairs in the style
|
|
|
2375 // of environment variables. Start by converting ':' to NUL.
|
|
|
2376
|
|
|
2377 if (SyncKnobs == NULL) SyncKnobs = "" ;
|
|
|
2378
|
|
|
2379 size_t sz = strlen (SyncKnobs) ;
|
|
|
2380 char * knobs = (char *) malloc (sz + 2) ;
|
|
|
2381 if (knobs == NULL) {
|
|
|
2382 vm_exit_out_of_memory (sz + 2, "Parse SyncKnobs") ;
|
|
|
2383 guarantee (0, "invariant") ;
|
|
|
2384 }
|
|
|
2385 strcpy (knobs, SyncKnobs) ;
|
|
|
2386 knobs[sz+1] = 0 ;
|
|
|
2387 for (char * p = knobs ; *p ; p++) {
|
|
|
2388 if (*p == ':') *p = 0 ;
|
|
|
2389 }
|
|
|
2390
|
|
|
2391 #define SETKNOB(x) { Knob_##x = kvGetInt (knobs, #x, Knob_##x); }
|
|
|
2392 SETKNOB(ReportSettings) ;
|
|
|
2393 SETKNOB(Verbose) ;
|
|
|
2394 SETKNOB(FixedSpin) ;
|
|
|
2395 SETKNOB(SpinLimit) ;
|
|
|
2396 SETKNOB(SpinBase) ;
|
|
|
2397 SETKNOB(SpinBackOff);
|
|
|
2398 SETKNOB(CASPenalty) ;
|
|
|
2399 SETKNOB(OXPenalty) ;
|
|
|
2400 SETKNOB(LogSpins) ;
|
|
|
2401 SETKNOB(SpinSetSucc) ;
|
|
|
2402 SETKNOB(SuccEnabled) ;
|
|
|
2403 SETKNOB(SuccRestrict) ;
|
|
|
2404 SETKNOB(Penalty) ;
|
|
|
2405 SETKNOB(Bonus) ;
|
|
|
2406 SETKNOB(BonusB) ;
|
|
|
2407 SETKNOB(Poverty) ;
|
|
|
2408 SETKNOB(SpinAfterFutile) ;
|
|
|
2409 SETKNOB(UsePause) ;
|
|
|
2410 SETKNOB(SpinEarly) ;
|
|
|
2411 SETKNOB(OState) ;
|
|
|
2412 SETKNOB(MaxSpinners) ;
|
|
|
2413 SETKNOB(PreSpin) ;
|
|
|
2414 SETKNOB(ExitPolicy) ;
|
|
|
2415 SETKNOB(QMode);
|
|
|
2416 SETKNOB(ResetEvent) ;
|
|
|
2417 SETKNOB(MoveNotifyee) ;
|
|
|
2418 SETKNOB(FastHSSEC) ;
|
|
|
2419 #undef SETKNOB
|
|
|
2420
|
|
|
2421 if (os::is_MP()) {
|
|
|
2422 BackOffMask = (1 << Knob_SpinBackOff) - 1 ;
|
|
|
2423 if (Knob_ReportSettings) ::printf ("BackOffMask=%X\n", BackOffMask) ;
|
|
|
2424 // CONSIDER: BackOffMask = ROUNDUP_NEXT_POWER2 (ncpus-1)
|
|
|
2425 } else {
|
|
|
2426 Knob_SpinLimit = 0 ;
|
|
|
2427 Knob_SpinBase = 0 ;
|
|
|
2428 Knob_PreSpin = 0 ;
|
|
|
2429 Knob_FixedSpin = -1 ;
|
|
|
2430 }
|
|
|
2431
|
|
|
2432 if (Knob_LogSpins == 0) {
|
|
|
2433 ObjectMonitor::_sync_FailedSpins = NULL ;
|
|
|
2434 }
|
|
|
2435
|
|
|
2436 free (knobs) ;
|
|
|
2437 OrderAccess::fence() ;
|
|
|
2438 InitDone = 1 ;
|
|
|
2439 }
|
|
|
2440
|
|
|
2441 #ifndef PRODUCT
|
|
|
2442 void ObjectMonitor::verify() {
|
|
|
2443 }
|
|
|
2444
|
|
|
2445 void ObjectMonitor::print() {
|
|
|
2446 }
|
|
|
2447 #endif
|
