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1878
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1 /*
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2 * Copyright (c) 2003, 2007, Oracle and/or its affiliates. All rights reserved.
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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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25 # include "incls/_precompiled.incl"
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26 # include "incls/_jvmtiRawMonitor.cpp.incl"
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27
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28 GrowableArray<JvmtiRawMonitor*> *JvmtiPendingMonitors::_monitors = new (ResourceObj::C_HEAP) GrowableArray<JvmtiRawMonitor*>(1,true);
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29
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30 void JvmtiPendingMonitors::transition_raw_monitors() {
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31 assert((Threads::number_of_threads()==1),
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32 "Java thread has not created yet or more than one java thread \
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33 is running. Raw monitor transition will not work");
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34 JavaThread *current_java_thread = JavaThread::current();
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35 assert(current_java_thread->thread_state() == _thread_in_vm, "Must be in vm");
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36 {
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37 ThreadBlockInVM __tbivm(current_java_thread);
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38 for(int i=0; i< count(); i++) {
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39 JvmtiRawMonitor *rmonitor = monitors()->at(i);
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40 int r = rmonitor->raw_enter(current_java_thread);
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41 assert(r == ObjectMonitor::OM_OK, "raw_enter should have worked");
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42 }
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43 }
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44 // pending monitors are converted to real monitor so delete them all.
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45 dispose();
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46 }
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47
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48 //
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49 // class JvmtiRawMonitor
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50 //
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51
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52 JvmtiRawMonitor::JvmtiRawMonitor(const char *name) {
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53 #ifdef ASSERT
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54 _name = strcpy(NEW_C_HEAP_ARRAY(char, strlen(name) + 1), name);
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55 #else
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56 _name = NULL;
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57 #endif
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58 _magic = JVMTI_RM_MAGIC;
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59 }
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60
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61 JvmtiRawMonitor::~JvmtiRawMonitor() {
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62 #ifdef ASSERT
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63 FreeHeap(_name);
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64 #endif
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65 _magic = 0;
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66 }
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67
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68
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69 bool
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70 JvmtiRawMonitor::is_valid() {
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71 int value = 0;
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72
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73 // This object might not be a JvmtiRawMonitor so we can't assume
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74 // the _magic field is properly aligned. Get the value in a safe
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75 // way and then check against JVMTI_RM_MAGIC.
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76
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77 switch (sizeof(_magic)) {
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78 case 2:
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79 value = Bytes::get_native_u2((address)&_magic);
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80 break;
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81
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82 case 4:
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83 value = Bytes::get_native_u4((address)&_magic);
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84 break;
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85
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86 case 8:
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87 value = Bytes::get_native_u8((address)&_magic);
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88 break;
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89
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90 default:
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91 guarantee(false, "_magic field is an unexpected size");
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92 }
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93
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94 return value == JVMTI_RM_MAGIC;
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95 }
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96
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97 // -------------------------------------------------------------------------
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98 // The raw monitor subsystem is entirely distinct from normal
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99 // java-synchronization or jni-synchronization. raw monitors are not
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100 // associated with objects. They can be implemented in any manner
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101 // that makes sense. The original implementors decided to piggy-back
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102 // the raw-monitor implementation on the existing Java objectMonitor mechanism.
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103 // This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
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104 // Specifically, we should not implement raw monitors via java monitors.
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105 // Time permitting, we should disentangle and deconvolve the two implementations
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106 // and move the resulting raw monitor implementation over to the JVMTI directories.
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107 // Ideally, the raw monitor implementation would be built on top of
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108 // park-unpark and nothing else.
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109 //
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110 // raw monitors are used mainly by JVMTI
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111 // The raw monitor implementation borrows the ObjectMonitor structure,
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112 // but the operators are degenerate and extremely simple.
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113 //
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114 // Mixed use of a single objectMonitor instance -- as both a raw monitor
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115 // and a normal java monitor -- is not permissible.
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116 //
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117 // Note that we use the single RawMonitor_lock to protect queue operations for
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118 // _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
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119 // is deprecated and rare, this is not of concern. The RawMonitor_lock can not
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120 // be held indefinitely. The critical sections must be short and bounded.
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121 //
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122 // -------------------------------------------------------------------------
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123
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124 int JvmtiRawMonitor::SimpleEnter (Thread * Self) {
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125 for (;;) {
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126 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
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127 return OS_OK ;
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128 }
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129
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130 ObjectWaiter Node (Self) ;
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131 Self->_ParkEvent->reset() ; // strictly optional
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132 Node.TState = ObjectWaiter::TS_ENTER ;
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133
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134 RawMonitor_lock->lock_without_safepoint_check() ;
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135 Node._next = _EntryList ;
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136 _EntryList = &Node ;
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137 OrderAccess::fence() ;
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138 if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
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139 _EntryList = Node._next ;
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140 RawMonitor_lock->unlock() ;
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141 return OS_OK ;
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142 }
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143 RawMonitor_lock->unlock() ;
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144 while (Node.TState == ObjectWaiter::TS_ENTER) {
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145 Self->_ParkEvent->park() ;
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146 }
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147 }
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148 }
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149
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150 int JvmtiRawMonitor::SimpleExit (Thread * Self) {
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151 guarantee (_owner == Self, "invariant") ;
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152 OrderAccess::release_store_ptr (&_owner, NULL) ;
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153 OrderAccess::fence() ;
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154 if (_EntryList == NULL) return OS_OK ;
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155 ObjectWaiter * w ;
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156
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157 RawMonitor_lock->lock_without_safepoint_check() ;
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158 w = _EntryList ;
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159 if (w != NULL) {
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160 _EntryList = w->_next ;
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161 }
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162 RawMonitor_lock->unlock() ;
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163 if (w != NULL) {
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164 guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
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165 ParkEvent * ev = w->_event ;
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166 w->TState = ObjectWaiter::TS_RUN ;
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167 OrderAccess::fence() ;
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168 ev->unpark() ;
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169 }
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170 return OS_OK ;
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171 }
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172
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173 int JvmtiRawMonitor::SimpleWait (Thread * Self, jlong millis) {
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174 guarantee (_owner == Self , "invariant") ;
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175 guarantee (_recursions == 0, "invariant") ;
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176
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177 ObjectWaiter Node (Self) ;
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178 Node._notified = 0 ;
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179 Node.TState = ObjectWaiter::TS_WAIT ;
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180
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181 RawMonitor_lock->lock_without_safepoint_check() ;
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182 Node._next = _WaitSet ;
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183 _WaitSet = &Node ;
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184 RawMonitor_lock->unlock() ;
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185
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186 SimpleExit (Self) ;
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187 guarantee (_owner != Self, "invariant") ;
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188
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189 int ret = OS_OK ;
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190 if (millis <= 0) {
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191 Self->_ParkEvent->park();
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192 } else {
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193 ret = Self->_ParkEvent->park(millis);
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194 }
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195
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196 // If thread still resides on the waitset then unlink it.
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197 // Double-checked locking -- the usage is safe in this context
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198 // as we TState is volatile and the lock-unlock operators are
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199 // serializing (barrier-equivalent).
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200
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201 if (Node.TState == ObjectWaiter::TS_WAIT) {
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202 RawMonitor_lock->lock_without_safepoint_check() ;
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203 if (Node.TState == ObjectWaiter::TS_WAIT) {
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204 // Simple O(n) unlink, but performance isn't critical here.
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205 ObjectWaiter * p ;
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206 ObjectWaiter * q = NULL ;
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207 for (p = _WaitSet ; p != &Node; p = p->_next) {
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208 q = p ;
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209 }
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210 guarantee (p == &Node, "invariant") ;
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211 if (q == NULL) {
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212 guarantee (p == _WaitSet, "invariant") ;
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213 _WaitSet = p->_next ;
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214 } else {
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215 guarantee (p == q->_next, "invariant") ;
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216 q->_next = p->_next ;
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217 }
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218 Node.TState = ObjectWaiter::TS_RUN ;
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219 }
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220 RawMonitor_lock->unlock() ;
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221 }
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222
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223 guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
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224 SimpleEnter (Self) ;
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225
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226 guarantee (_owner == Self, "invariant") ;
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227 guarantee (_recursions == 0, "invariant") ;
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228 return ret ;
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229 }
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230
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231 int JvmtiRawMonitor::SimpleNotify (Thread * Self, bool All) {
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232 guarantee (_owner == Self, "invariant") ;
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233 if (_WaitSet == NULL) return OS_OK ;
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234
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235 // We have two options:
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236 // A. Transfer the threads from the WaitSet to the EntryList
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237 // B. Remove the thread from the WaitSet and unpark() it.
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238 //
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239 // We use (B), which is crude and results in lots of futile
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240 // context switching. In particular (B) induces lots of contention.
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241
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242 ParkEvent * ev = NULL ; // consider using a small auto array ...
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243 RawMonitor_lock->lock_without_safepoint_check() ;
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244 for (;;) {
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245 ObjectWaiter * w = _WaitSet ;
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246 if (w == NULL) break ;
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247 _WaitSet = w->_next ;
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248 if (ev != NULL) { ev->unpark(); ev = NULL; }
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249 ev = w->_event ;
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250 OrderAccess::loadstore() ;
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251 w->TState = ObjectWaiter::TS_RUN ;
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252 OrderAccess::storeload();
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253 if (!All) break ;
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254 }
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255 RawMonitor_lock->unlock() ;
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256 if (ev != NULL) ev->unpark();
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257 return OS_OK ;
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258 }
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259
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260 // Any JavaThread will enter here with state _thread_blocked
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261 int JvmtiRawMonitor::raw_enter(TRAPS) {
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262 TEVENT (raw_enter) ;
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263 void * Contended ;
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264
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265 // don't enter raw monitor if thread is being externally suspended, it will
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266 // surprise the suspender if a "suspended" thread can still enter monitor
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267 JavaThread * jt = (JavaThread *)THREAD;
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268 if (THREAD->is_Java_thread()) {
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269 jt->SR_lock()->lock_without_safepoint_check();
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270 while (jt->is_external_suspend()) {
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271 jt->SR_lock()->unlock();
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272 jt->java_suspend_self();
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273 jt->SR_lock()->lock_without_safepoint_check();
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274 }
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275 // guarded by SR_lock to avoid racing with new external suspend requests.
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276 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
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277 jt->SR_lock()->unlock();
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278 } else {
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279 Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
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280 }
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281
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282 if (Contended == THREAD) {
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283 _recursions ++ ;
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284 return OM_OK ;
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285 }
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286
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287 if (Contended == NULL) {
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288 guarantee (_owner == THREAD, "invariant") ;
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289 guarantee (_recursions == 0, "invariant") ;
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290 return OM_OK ;
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291 }
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292
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293 THREAD->set_current_pending_monitor(this);
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294
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295 if (!THREAD->is_Java_thread()) {
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296 // No other non-Java threads besides VM thread would acquire
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297 // a raw monitor.
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298 assert(THREAD->is_VM_thread(), "must be VM thread");
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299 SimpleEnter (THREAD) ;
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300 } else {
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301 guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
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302 for (;;) {
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303 jt->set_suspend_equivalent();
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304 // cleared by handle_special_suspend_equivalent_condition() or
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305 // java_suspend_self()
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306 SimpleEnter (THREAD) ;
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307
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308 // were we externally suspended while we were waiting?
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309 if (!jt->handle_special_suspend_equivalent_condition()) break ;
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310
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311 // This thread was externally suspended
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312 //
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313 // This logic isn't needed for JVMTI raw monitors,
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314 // but doesn't hurt just in case the suspend rules change. This
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315 // logic is needed for the JvmtiRawMonitor.wait() reentry phase.
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316 // We have reentered the contended monitor, but while we were
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317 // waiting another thread suspended us. We don't want to reenter
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318 // the monitor while suspended because that would surprise the
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319 // thread that suspended us.
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320 //
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321 // Drop the lock -
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322 SimpleExit (THREAD) ;
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323
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324 jt->java_suspend_self();
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325 }
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326
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327 assert(_owner == THREAD, "Fatal error with monitor owner!");
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328 assert(_recursions == 0, "Fatal error with monitor recursions!");
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329 }
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330
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331 THREAD->set_current_pending_monitor(NULL);
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332 guarantee (_recursions == 0, "invariant") ;
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333 return OM_OK;
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334 }
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335
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336 // Used mainly for JVMTI raw monitor implementation
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337 // Also used for JvmtiRawMonitor::wait().
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338 int JvmtiRawMonitor::raw_exit(TRAPS) {
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339 TEVENT (raw_exit) ;
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340 if (THREAD != _owner) {
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341 return OM_ILLEGAL_MONITOR_STATE;
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342 }
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343 if (_recursions > 0) {
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344 --_recursions ;
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345 return OM_OK ;
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346 }
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347
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348 void * List = _EntryList ;
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349 SimpleExit (THREAD) ;
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350
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351 return OM_OK;
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352 }
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353
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354 // Used for JVMTI raw monitor implementation.
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355 // All JavaThreads will enter here with state _thread_blocked
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356
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357 int JvmtiRawMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
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358 TEVENT (raw_wait) ;
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359 if (THREAD != _owner) {
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360 return OM_ILLEGAL_MONITOR_STATE;
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361 }
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362
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363 // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
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364 // The caller must be able to tolerate spurious returns from raw_wait().
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365 THREAD->_ParkEvent->reset() ;
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366 OrderAccess::fence() ;
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367
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368 // check interrupt event
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369 if (interruptible && Thread::is_interrupted(THREAD, true)) {
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370 return OM_INTERRUPTED;
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371 }
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372
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373 intptr_t save = _recursions ;
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374 _recursions = 0 ;
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375 _waiters ++ ;
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376 if (THREAD->is_Java_thread()) {
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377 guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
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378 ((JavaThread *)THREAD)->set_suspend_equivalent();
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379 }
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380 int rv = SimpleWait (THREAD, millis) ;
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381 _recursions = save ;
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382 _waiters -- ;
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383
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384 guarantee (THREAD == _owner, "invariant") ;
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385 if (THREAD->is_Java_thread()) {
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386 JavaThread * jSelf = (JavaThread *) THREAD ;
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387 for (;;) {
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388 if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
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389 SimpleExit (THREAD) ;
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390 jSelf->java_suspend_self();
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391 SimpleEnter (THREAD) ;
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392 jSelf->set_suspend_equivalent() ;
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393 }
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394 }
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395 guarantee (THREAD == _owner, "invariant") ;
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396
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397 if (interruptible && Thread::is_interrupted(THREAD, true)) {
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398 return OM_INTERRUPTED;
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399 }
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400 return OM_OK ;
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401 }
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402
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403 int JvmtiRawMonitor::raw_notify(TRAPS) {
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404 TEVENT (raw_notify) ;
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405 if (THREAD != _owner) {
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406 return OM_ILLEGAL_MONITOR_STATE;
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407 }
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408 SimpleNotify (THREAD, false) ;
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409 return OM_OK;
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|
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410 }
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|
|
411
|
|
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412 int JvmtiRawMonitor::raw_notifyAll(TRAPS) {
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413 TEVENT (raw_notifyAll) ;
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414 if (THREAD != _owner) {
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415 return OM_ILLEGAL_MONITOR_STATE;
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|
|
416 }
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417 SimpleNotify (THREAD, true) ;
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418 return OM_OK;
|
|
|
419 }
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|
|
420
|
