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1878
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1 /*
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1972
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2 * Copyright (c) 2003, 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 "prims/jvmtiRawMonitor.hpp"
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27 #include "runtime/interfaceSupport.hpp"
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28 #include "runtime/thread.hpp"
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1878
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29
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6197
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30 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<JvmtiRawMonitor*>(1,true);
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1878
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31
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32 void JvmtiPendingMonitors::transition_raw_monitors() {
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33 assert((Threads::number_of_threads()==1),
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34 "Java thread has not created yet or more than one java thread \
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35 is running. Raw monitor transition will not work");
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36 JavaThread *current_java_thread = JavaThread::current();
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37 assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");
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38 {
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39 ThreadBlockInVM __tbivm(current_java_thread);
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40 for(int i=0; i< count(); i++) {
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41 JvmtiRawMonitor *rmonitor = monitors()->at(i);
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42 int r = rmonitor->raw_enter(current_java_thread);
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43 assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");
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44 }
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45 }
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46 // pending monitors are converted to real monitor so delete them all.
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47 dispose();
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48 }
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49
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50 //
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51 // class JvmtiRawMonitor
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52 //
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53
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54 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {
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55 #ifdef ASSERT
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6197
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56 _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1, mtInternal), name);
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1878
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57 #else
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58 _name = NULL;
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59 #endif
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60 _magic = JVMTI_RM_MAGIC;
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61 }
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62
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63 JvmtiRawMonitor::~JvmtiRawMonitor() {
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64 #ifdef ASSERT
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65 FreeHeap(_name);
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66 #endif
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67 _magic = 0;
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68 }
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69
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70
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71 bool
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72 JvmtiRawMonitor::is_valid() {
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73 int value = 0;
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74
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75 // This object might not be a JvmtiRawMonitor so we can't assume
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76 // the _magic field is properly aligned. Get the value in a safe
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77 // way and then check against JVMTI_RM_MAGIC.
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78
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79 switch (sizeof(_magic)) {
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80 case 2:
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81 value = Bytes::get_native_u2((address)&_magic);
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82 break;
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83
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84 case 4:
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85 value = Bytes::get_native_u4((address)&_magic);
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86 break;
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87
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88 case 8:
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89 value = Bytes::get_native_u8((address)&_magic);
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90 break;
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91
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92 default:
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93 guarantee(false, "_magic field is an unexpected size");
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94 }
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95
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96 return value == JVMTI_RM_MAGIC;
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97 }
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98
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99 // -------------------------------------------------------------------------
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100 // The raw monitor subsystem is entirely distinct from normal
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101 // java-synchronization or jni-synchronization. raw monitors are not
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102 // associated with objects. They can be implemented in any manner
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103 // that makes sense. The original implementors decided to piggy-back
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104 // the raw-monitor implementation on the existing Java objectMonitor mechanism.
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105 // This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
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106 // Specifically, we should not implement raw monitors via java monitors.
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107 // Time permitting, we should disentangle and deconvolve the two implementations
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108 // and move the resulting raw monitor implementation over to the JVMTI directories.
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109 // Ideally, the raw monitor implementation would be built on top of
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110 // park-unpark and nothing else.
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111 //
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112 // raw monitors are used mainly by JVMTI
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113 // The raw monitor implementation borrows the ObjectMonitor structure,
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114 // but the operators are degenerate and extremely simple.
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115 //
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116 // Mixed use of a single objectMonitor instance -- as both a raw monitor
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117 // and a normal java monitor -- is not permissible.
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118 //
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119 // Note that we use the single RawMonitor_lock to protect queue operations for
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120 // _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
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121 // is deprecated and rare, this is not of concern. The RawMonitor_lock can not
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122 // be held indefinitely. The critical sections must be short and bounded.
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123 //
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124 // -------------------------------------------------------------------------
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125
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126 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {
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127 for (;;) {
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128 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
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129 return OS_OK ;
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130 }
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131
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132 ObjectWaiter Node (Self) ;
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133 Self->_ParkEvent->reset() ; // strictly optional
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134 Node.TState = ObjectWaiter::TS_ENTER ;
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135
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136 RawMonitor_lock->lock_without_safepoint_check() ;
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137 Node._next = _EntryList ;
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138 _EntryList = &Node ;
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139 OrderAccess::fence() ;
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140 if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
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141 _EntryList = Node._next ;
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142 RawMonitor_lock->unlock() ;
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143 return OS_OK ;
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144 }
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145 RawMonitor_lock->unlock() ;
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146 while (Node.TState == ObjectWaiter::TS_ENTER) {
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147 Self->_ParkEvent->park() ;
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148 }
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149 }
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150 }
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151
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152 int JvmtiRawMonitor::SimpleExit (Thread * Self) {
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153 guarantee (_owner == Self, "invariant") ;
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154 OrderAccess::release_store_ptr (&_owner, NULL) ;
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155 OrderAccess::fence() ;
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156 if (_EntryList == NULL) return OS_OK ;
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157 ObjectWaiter * w ;
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158
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159 RawMonitor_lock->lock_without_safepoint_check() ;
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160 w = _EntryList ;
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161 if (w != NULL) {
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162 _EntryList = w->_next ;
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163 }
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164 RawMonitor_lock->unlock() ;
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165 if (w != NULL) {
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166 guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
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167 ParkEvent * ev = w->_event ;
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168 w->TState = ObjectWaiter::TS_RUN ;
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169 OrderAccess::fence() ;
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170 ev->unpark() ;
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171 }
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172 return OS_OK ;
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173 }
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174
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175 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {
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176 guarantee (_owner == Self , "invariant") ;
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177 guarantee (_recursions == 0, "invariant") ;
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178
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179 ObjectWaiter Node (Self) ;
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180 Node._notified = 0 ;
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181 Node.TState = ObjectWaiter::TS_WAIT ;
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182
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183 RawMonitor_lock->lock_without_safepoint_check() ;
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184 Node._next = _WaitSet ;
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185 _WaitSet = &Node ;
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186 RawMonitor_lock->unlock() ;
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187
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188 SimpleExit (Self) ;
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189 guarantee (_owner != Self, "invariant") ;
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190
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191 int ret = OS_OK ;
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192 if (millis <= 0) {
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193 Self->_ParkEvent->park();
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194 } else {
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195 ret = Self->_ParkEvent->park(millis);
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196 }
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197
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198 // If thread still resides on the waitset then unlink it.
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199 // Double-checked locking -- the usage is safe in this context
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200 // as we TState is volatile and the lock-unlock operators are
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201 // serializing (barrier-equivalent).
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202
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203 if (Node.TState == ObjectWaiter::TS_WAIT) {
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204 RawMonitor_lock->lock_without_safepoint_check() ;
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205 if (Node.TState == ObjectWaiter::TS_WAIT) {
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206 // Simple O(n) unlink, but performance isn't critical here.
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207 ObjectWaiter * p ;
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208 ObjectWaiter * q = NULL ;
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209 for (p = _WaitSet ; p != &Node; p = p->_next) {
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210 q = p ;
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211 }
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212 guarantee (p == &Node, "invariant") ;
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213 if (q == NULL) {
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214 guarantee (p == _WaitSet, "invariant") ;
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215 _WaitSet = p->_next ;
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216 } else {
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217 guarantee (p == q->_next, "invariant") ;
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218 q->_next = p->_next ;
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219 }
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220 Node.TState = ObjectWaiter::TS_RUN ;
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221 }
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222 RawMonitor_lock->unlock() ;
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223 }
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224
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225 guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
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226 SimpleEnter (Self) ;
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227
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228 guarantee (_owner == Self, "invariant") ;
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229 guarantee (_recursions == 0, "invariant") ;
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230 return ret ;
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231 }
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232
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233 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {
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234 guarantee (_owner == Self, "invariant") ;
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235 if (_WaitSet == NULL) return OS_OK ;
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236
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237 // We have two options:
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238 // A. Transfer the threads from the WaitSet to the EntryList
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239 // B. Remove the thread from the WaitSet and unpark() it.
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240 //
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241 // We use (B), which is crude and results in lots of futile
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242 // context switching. In particular (B) induces lots of contention.
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243
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244 ParkEvent * ev = NULL ; // consider using a small auto array ...
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245 RawMonitor_lock->lock_without_safepoint_check() ;
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246 for (;;) {
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247 ObjectWaiter * w = _WaitSet ;
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248 if (w == NULL) break ;
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249 _WaitSet = w->_next ;
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250 if (ev != NULL) { ev->unpark(); ev = NULL; }
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251 ev = w->_event ;
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252 OrderAccess::loadstore() ;
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253 w->TState = ObjectWaiter::TS_RUN ;
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254 OrderAccess::storeload();
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255 if (!All) break ;
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256 }
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257 RawMonitor_lock->unlock() ;
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258 if (ev != NULL) ev->unpark();
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259 return OS_OK ;
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260 }
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261
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262 // Any JavaThread will enter here with state _thread_blocked
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263 int JvmtiRawMonitor::raw_enter(TRAPS) {
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264 TEVENT (raw_enter) ;
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265 void * Contended ;
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266
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267 // don't enter raw monitor if thread is being externally suspended, it will
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268 // surprise the suspender if a "suspended" thread can still enter monitor
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269 JavaThread * jt = (JavaThread *)THREAD;
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270 if (THREAD->is_Java_thread()) {
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271 jt->SR_lock()->lock_without_safepoint_check();
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272 while (jt->is_external_suspend()) {
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273 jt->SR_lock()->unlock();
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274 jt->java_suspend_self();
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275 jt->SR_lock()->lock_without_safepoint_check();
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276 }
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277 // guarded by SR_lock to avoid racing with new external suspend requests.
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278 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
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279 jt->SR_lock()->unlock();
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280 } else {
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281 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
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282 }
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283
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284 if (Contended == THREAD) {
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285 _recursions ++ ;
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286 return OM_OK ;
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287 }
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288
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289 if (Contended == NULL) {
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290 guarantee (_owner == THREAD, "invariant") ;
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291 guarantee (_recursions == 0, "invariant") ;
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292 return OM_OK ;
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293 }
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294
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295 THREAD->set_current_pending_monitor(this);
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296
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297 if (!THREAD->is_Java_thread()) {
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298 // No other non-Java threads besides VM thread would acquire
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299 // a raw monitor.
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300 assert(THREAD->is_VM_thread(), "must be VM thread");
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301 SimpleEnter (THREAD) ;
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302 } else {
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303 guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
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304 for (;;) {
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305 jt->set_suspend_equivalent();
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306 // cleared by handle_special_suspend_equivalent_condition() or
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307 // java_suspend_self()
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308 SimpleEnter (THREAD) ;
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309
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310 // were we externally suspended while we were waiting?
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311 if (!jt->handle_special_suspend_equivalent_condition()) break ;
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312
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313 // This thread was externally suspended
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314 //
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315 // This logic isn't needed for JVMTI raw monitors,
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316 // but doesn't hurt just in case the suspend rules change. This
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317 // logic is needed for the JvmtiRawMonitor.wait() reentry phase.
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318 // We have reentered the contended monitor, but while we were
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319 // waiting another thread suspended us. We don't want to reenter
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320 // the monitor while suspended because that would surprise the
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321 // thread that suspended us.
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322 //
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323 // Drop the lock -
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324 SimpleExit (THREAD) ;
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325
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326 jt->java_suspend_self();
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327 }
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328
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329 assert(_owner == THREAD, "Fatal error with monitor owner!");
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330 assert(_recursions == 0, "Fatal error with monitor recursions!");
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331 }
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332
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333 THREAD->set_current_pending_monitor(NULL);
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334 guarantee (_recursions == 0, "invariant") ;
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335 return OM_OK;
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336 }
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337
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338 // Used mainly for JVMTI raw monitor implementation
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339 // Also used for JvmtiRawMonitor::wait().
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340 int JvmtiRawMonitor::raw_exit(TRAPS) {
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341 TEVENT (raw_exit) ;
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342 if (THREAD != _owner) {
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343 return OM_ILLEGAL_MONITOR_STATE;
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344 }
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345 if (_recursions > 0) {
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346 --_recursions ;
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347 return OM_OK ;
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348 }
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349
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350 void * List = _EntryList ;
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351 SimpleExit (THREAD) ;
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352
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353 return OM_OK;
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354 }
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355
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356 // Used for JVMTI raw monitor implementation.
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357 // All JavaThreads will enter here with state _thread_blocked
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358
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359 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
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360 TEVENT (raw_wait) ;
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361 if (THREAD != _owner) {
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362 return OM_ILLEGAL_MONITOR_STATE;
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363 }
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364
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365 // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
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366 // The caller must be able to tolerate spurious returns from raw_wait().
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367 THREAD->_ParkEvent->reset() ;
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368 OrderAccess::fence() ;
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369
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370 // check interrupt event
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371 if (interruptible && Thread::is_interrupted(THREAD, true)) {
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372 return OM_INTERRUPTED;
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373 }
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374
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375 intptr_t save = _recursions ;
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376 _recursions = 0 ;
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377 _waiters ++ ;
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378 if (THREAD->is_Java_thread()) {
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379 guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
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380 ((JavaThread *)THREAD)->set_suspend_equivalent();
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381 }
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382 int rv = SimpleWait (THREAD, millis) ;
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383 _recursions = save ;
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384 _waiters -- ;
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385
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386 guarantee (THREAD == _owner, "invariant") ;
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387 if (THREAD->is_Java_thread()) {
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388 JavaThread * jSelf = (JavaThread *) THREAD ;
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389 for (;;) {
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390 if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
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391 SimpleExit (THREAD) ;
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392 jSelf->java_suspend_self();
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393 SimpleEnter (THREAD) ;
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394 jSelf->set_suspend_equivalent() ;
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395 }
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396 }
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397 guarantee (THREAD == _owner, "invariant") ;
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398
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399 if (interruptible && Thread::is_interrupted(THREAD, true)) {
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400 return OM_INTERRUPTED;
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401 }
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402 return OM_OK ;
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403 }
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404
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405 int JvmtiRawMonitor::raw_notify(TRAPS) {
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406 TEVENT (raw_notify) ;
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407 if (THREAD != _owner) {
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408 return OM_ILLEGAL_MONITOR_STATE;
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409 }
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410 SimpleNotify (THREAD, false) ;
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411 return OM_OK;
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412 }
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413
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414 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {
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415 TEVENT (raw_notifyAll) ;
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416 if (THREAD != _owner) {
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417 return OM_ILLEGAL_MONITOR_STATE;
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418 }
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419 SimpleNotify (THREAD, true) ;
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420 return OM_OK;
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421 }
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422
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