0
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1
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2 /*
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3 * Copyright 2005-2007 Sun Microsystems, Inc. All Rights Reserved.
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4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 *
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6 * This code is free software; you can redistribute it and/or modify it
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7 * under the terms of the GNU General Public License version 2 only, as
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8 * published by the Free Software Foundation.
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9 *
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10 * This code is distributed in the hope that it will be useful, but WITHOUT
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11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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13 * version 2 for more details (a copy is included in the LICENSE file that
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14 * accompanied this code).
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15 *
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16 * You should have received a copy of the GNU General Public License version
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17 * 2 along with this work; if not, write to the Free Software Foundation,
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18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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19 *
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20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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21 * CA 95054 USA or visit www.sun.com if you need additional information or
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22 * have any questions.
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23 *
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24 */
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25
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26 # include "incls/_precompiled.incl"
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27 # include "incls/_biasedLocking.cpp.incl"
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28
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29 static bool _biased_locking_enabled = false;
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30 BiasedLockingCounters BiasedLocking::_counters;
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31
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32 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
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33 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
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34
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35 static void enable_biased_locking(klassOop k) {
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36 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype());
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37 }
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38
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39 class VM_EnableBiasedLocking: public VM_Operation {
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40 public:
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41 VM_EnableBiasedLocking() {}
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42 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
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43 void doit() {
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44 // Iterate the system dictionary enabling biased locking for all
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45 // currently loaded classes
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46 SystemDictionary::classes_do(enable_biased_locking);
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47 // Indicate that future instances should enable it as well
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48 _biased_locking_enabled = true;
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49
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50 if (TraceBiasedLocking) {
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51 tty->print_cr("Biased locking enabled");
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52 }
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53 }
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54
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55 bool allow_nested_vm_operations() const { return false; }
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56 };
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57
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58
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59 // One-shot PeriodicTask subclass for enabling biased locking
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60 class EnableBiasedLockingTask : public PeriodicTask {
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61 public:
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62 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
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63
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64 virtual void task() {
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65 VM_EnableBiasedLocking op;
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66 VMThread::execute(&op);
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67
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68 // Reclaim our storage and disenroll ourself
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69 delete this;
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70 }
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71 };
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72
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73
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74 void BiasedLocking::init() {
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75 // If biased locking is enabled, schedule a task to fire a few
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76 // seconds into the run which turns on biased locking for all
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77 // currently loaded classes as well as future ones. This is a
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78 // workaround for startup time regressions due to a large number of
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79 // safepoints being taken during VM startup for bias revocation.
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80 // Ideally we would have a lower cost for individual bias revocation
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81 // and not need a mechanism like this.
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82 if (UseBiasedLocking) {
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83 if (BiasedLockingStartupDelay > 0) {
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84 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
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85 task->enroll();
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86 } else {
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87 VM_EnableBiasedLocking op;
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88 VMThread::execute(&op);
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89 }
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90 }
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91 }
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92
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93
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94 bool BiasedLocking::enabled() {
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95 return _biased_locking_enabled;
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96 }
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97
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98 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
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99 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
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100 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
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101 if (info != NULL) {
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102 return info;
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103 }
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104
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105 info = new GrowableArray<MonitorInfo*>();
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106
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107 // It's possible for the thread to not have any Java frames on it,
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108 // i.e., if it's the main thread and it's already returned from main()
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109 if (thread->has_last_Java_frame()) {
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110 RegisterMap rm(thread);
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111 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
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112 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
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113 if (monitors != NULL) {
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114 int len = monitors->length();
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115 // Walk monitors youngest to oldest
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116 for (int i = len - 1; i >= 0; i--) {
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117 MonitorInfo* mon_info = monitors->at(i);
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118 oop owner = mon_info->owner();
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119 if (owner != NULL) {
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120 info->append(mon_info);
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121 }
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122 }
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123 }
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124 }
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125 }
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126
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127 thread->set_cached_monitor_info(info);
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128 return info;
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129 }
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130
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131
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132 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
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133 markOop mark = obj->mark();
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134 if (!mark->has_bias_pattern()) {
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135 if (TraceBiasedLocking) {
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136 ResourceMark rm;
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137 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
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138 Klass::cast(obj->klass())->external_name());
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139 }
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140 return BiasedLocking::NOT_BIASED;
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141 }
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142
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143 int age = mark->age();
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144 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
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145 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
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146
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147 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
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148 ResourceMark rm;
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149 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT,
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150 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
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151 }
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152
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153 JavaThread* biased_thread = mark->biased_locker();
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154 if (biased_thread == NULL) {
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155 // Object is anonymously biased. We can get here if, for
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156 // example, we revoke the bias due to an identity hash code
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157 // being computed for an object.
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158 if (!allow_rebias) {
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159 obj->set_mark(unbiased_prototype);
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160 }
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161 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
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162 tty->print_cr(" Revoked bias of anonymously-biased object");
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163 }
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164 return BiasedLocking::BIAS_REVOKED;
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165 }
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166
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167 // Handle case where the thread toward which the object was biased has exited
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168 bool thread_is_alive = false;
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169 if (requesting_thread == biased_thread) {
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170 thread_is_alive = true;
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171 } else {
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172 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
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173 if (cur_thread == biased_thread) {
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174 thread_is_alive = true;
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175 break;
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176 }
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177 }
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178 }
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179 if (!thread_is_alive) {
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180 if (allow_rebias) {
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181 obj->set_mark(biased_prototype);
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182 } else {
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183 obj->set_mark(unbiased_prototype);
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184 }
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185 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
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186 tty->print_cr(" Revoked bias of object biased toward dead thread");
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187 }
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188 return BiasedLocking::BIAS_REVOKED;
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189 }
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190
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191 // Thread owning bias is alive.
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192 // Check to see whether it currently owns the lock and, if so,
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193 // write down the needed displaced headers to the thread's stack.
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194 // Otherwise, restore the object's header either to the unlocked
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195 // or unbiased state.
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196 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
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197 BasicLock* highest_lock = NULL;
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198 for (int i = 0; i < cached_monitor_info->length(); i++) {
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199 MonitorInfo* mon_info = cached_monitor_info->at(i);
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200 if (mon_info->owner() == obj) {
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201 if (TraceBiasedLocking && Verbose) {
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202 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
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203 (intptr_t) mon_info->owner(),
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204 (intptr_t) obj);
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205 }
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206 // Assume recursive case and fix up highest lock later
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207 markOop mark = markOopDesc::encode((BasicLock*) NULL);
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208 highest_lock = mon_info->lock();
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209 highest_lock->set_displaced_header(mark);
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210 } else {
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211 if (TraceBiasedLocking && Verbose) {
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212 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
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213 (intptr_t) mon_info->owner(),
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214 (intptr_t) obj);
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215 }
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216 }
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217 }
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218 if (highest_lock != NULL) {
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219 // Fix up highest lock to contain displaced header and point
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220 // object at it
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221 highest_lock->set_displaced_header(unbiased_prototype);
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222 // Reset object header to point to displaced mark
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223 obj->set_mark(markOopDesc::encode(highest_lock));
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224 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
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225 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
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226 tty->print_cr(" Revoked bias of currently-locked object");
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227 }
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228 } else {
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229 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
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230 tty->print_cr(" Revoked bias of currently-unlocked object");
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231 }
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232 if (allow_rebias) {
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233 obj->set_mark(biased_prototype);
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234 } else {
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235 // Store the unlocked value into the object's header.
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236 obj->set_mark(unbiased_prototype);
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237 }
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238 }
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239
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240 return BiasedLocking::BIAS_REVOKED;
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241 }
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242
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243
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244 enum HeuristicsResult {
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245 HR_NOT_BIASED = 1,
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246 HR_SINGLE_REVOKE = 2,
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247 HR_BULK_REBIAS = 3,
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248 HR_BULK_REVOKE = 4
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249 };
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250
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251
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252 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
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253 markOop mark = o->mark();
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254 if (!mark->has_bias_pattern()) {
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255 return HR_NOT_BIASED;
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256 }
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257
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258 // Heuristics to attempt to throttle the number of revocations.
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259 // Stages:
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260 // 1. Revoke the biases of all objects in the heap of this type,
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261 // but allow rebiasing of those objects if unlocked.
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262 // 2. Revoke the biases of all objects in the heap of this type
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263 // and don't allow rebiasing of these objects. Disable
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264 // allocation of objects of that type with the bias bit set.
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265 Klass* k = o->blueprint();
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266 jlong cur_time = os::javaTimeMillis();
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267 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
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268 int revocation_count = k->biased_lock_revocation_count();
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269 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
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270 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
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271 (last_bulk_revocation_time != 0) &&
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272 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
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273 // This is the first revocation we've seen in a while of an
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274 // object of this type since the last time we performed a bulk
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275 // rebiasing operation. The application is allocating objects in
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276 // bulk which are biased toward a thread and then handing them
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277 // off to another thread. We can cope with this allocation
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278 // pattern via the bulk rebiasing mechanism so we reset the
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279 // klass's revocation count rather than allow it to increase
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280 // monotonically. If we see the need to perform another bulk
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281 // rebias operation later, we will, and if subsequently we see
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282 // many more revocation operations in a short period of time we
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283 // will completely disable biasing for this type.
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284 k->set_biased_lock_revocation_count(0);
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285 revocation_count = 0;
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286 }
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287
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288 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
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289 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
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290 revocation_count = k->atomic_incr_biased_lock_revocation_count();
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291 }
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292
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293 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
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294 return HR_BULK_REVOKE;
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295 }
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296
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297 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
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298 return HR_BULK_REBIAS;
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299 }
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300
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301 return HR_SINGLE_REVOKE;
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302 }
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303
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304
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305 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
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306 bool bulk_rebias,
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307 bool attempt_rebias_of_object,
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308 JavaThread* requesting_thread) {
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309 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
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310
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311 if (TraceBiasedLocking) {
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312 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "
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313 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
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314 (bulk_rebias ? "rebias" : "revoke"),
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315 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name());
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316 }
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317
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318 jlong cur_time = os::javaTimeMillis();
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319 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time);
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320
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321
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322 klassOop k_o = o->klass();
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323 Klass* klass = Klass::cast(k_o);
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324
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325 if (bulk_rebias) {
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326 // Use the epoch in the klass of the object to implicitly revoke
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327 // all biases of objects of this data type and force them to be
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328 // reacquired. However, we also need to walk the stacks of all
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329 // threads and update the headers of lightweight locked objects
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330 // with biases to have the current epoch.
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331
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332 // If the prototype header doesn't have the bias pattern, don't
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333 // try to update the epoch -- assume another VM operation came in
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334 // and reset the header to the unbiased state, which will
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335 // implicitly cause all existing biases to be revoked
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336 if (klass->prototype_header()->has_bias_pattern()) {
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337 int prev_epoch = klass->prototype_header()->bias_epoch();
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338 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
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339 int cur_epoch = klass->prototype_header()->bias_epoch();
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340
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341 // Now walk all threads' stacks and adjust epochs of any biased
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342 // and locked objects of this data type we encounter
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343 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
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344 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
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345 for (int i = 0; i < cached_monitor_info->length(); i++) {
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346 MonitorInfo* mon_info = cached_monitor_info->at(i);
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347 oop owner = mon_info->owner();
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348 markOop mark = owner->mark();
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349 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
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350 // We might have encountered this object already in the case of recursive locking
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351 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
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352 owner->set_mark(mark->set_bias_epoch(cur_epoch));
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353 }
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354 }
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355 }
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356 }
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357
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358 // At this point we're done. All we have to do is potentially
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359 // adjust the header of the given object to revoke its bias.
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360 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
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361 } else {
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362 if (TraceBiasedLocking) {
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363 ResourceMark rm;
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364 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
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365 }
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366
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367 // Disable biased locking for this data type. Not only will this
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368 // cause future instances to not be biased, but existing biased
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369 // instances will notice that this implicitly caused their biases
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370 // to be revoked.
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371 klass->set_prototype_header(markOopDesc::prototype());
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372
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373 // Now walk all threads' stacks and forcibly revoke the biases of
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374 // any locked and biased objects of this data type we encounter.
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375 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
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376 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
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377 for (int i = 0; i < cached_monitor_info->length(); i++) {
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378 MonitorInfo* mon_info = cached_monitor_info->at(i);
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379 oop owner = mon_info->owner();
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380 markOop mark = owner->mark();
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381 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
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382 revoke_bias(owner, false, true, requesting_thread);
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383 }
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384 }
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385 }
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386
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387 // Must force the bias of the passed object to be forcibly revoked
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388 // as well to ensure guarantees to callers
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389 revoke_bias(o, false, true, requesting_thread);
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390 }
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391
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392 if (TraceBiasedLocking) {
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393 tty->print_cr("* Ending bulk revocation");
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394 }
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395
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396 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
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397
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398 if (attempt_rebias_of_object &&
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399 o->mark()->has_bias_pattern() &&
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400 klass->prototype_header()->has_bias_pattern()) {
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401 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
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402 klass->prototype_header()->bias_epoch());
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403 o->set_mark(new_mark);
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404 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
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405 if (TraceBiasedLocking) {
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406 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
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407 }
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408 }
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409
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410 assert(!o->mark()->has_bias_pattern() ||
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411 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
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412 "bug in bulk bias revocation");
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413
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414 return status_code;
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415 }
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416
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417
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418 static void clean_up_cached_monitor_info() {
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419 // Walk the thread list clearing out the cached monitors
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420 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
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421 thr->set_cached_monitor_info(NULL);
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422 }
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423 }
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424
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425
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426 class VM_RevokeBias : public VM_Operation {
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427 protected:
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428 Handle* _obj;
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429 GrowableArray<Handle>* _objs;
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430 JavaThread* _requesting_thread;
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431 BiasedLocking::Condition _status_code;
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432
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433 public:
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434 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
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435 : _obj(obj)
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436 , _objs(NULL)
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437 , _requesting_thread(requesting_thread)
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438 , _status_code(BiasedLocking::NOT_BIASED) {}
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439
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440 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
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441 : _obj(NULL)
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442 , _objs(objs)
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443 , _requesting_thread(requesting_thread)
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444 , _status_code(BiasedLocking::NOT_BIASED) {}
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445
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446 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
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447
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448 virtual bool doit_prologue() {
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449 // Verify that there is actual work to do since the callers just
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450 // give us locked object(s). If we don't find any biased objects
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451 // there is nothing to do and we avoid a safepoint.
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452 if (_obj != NULL) {
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453 markOop mark = (*_obj)()->mark();
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454 if (mark->has_bias_pattern()) {
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455 return true;
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456 }
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457 } else {
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458 for ( int i = 0 ; i < _objs->length(); i++ ) {
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459 markOop mark = (_objs->at(i))()->mark();
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460 if (mark->has_bias_pattern()) {
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461 return true;
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462 }
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463 }
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464 }
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465 return false;
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466 }
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467
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468 virtual void doit() {
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469 if (_obj != NULL) {
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470 if (TraceBiasedLocking) {
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471 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
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472 }
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473 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
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474 clean_up_cached_monitor_info();
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475 return;
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476 } else {
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477 if (TraceBiasedLocking) {
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478 tty->print_cr("Revoking bias with global safepoint:");
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479 }
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480 BiasedLocking::revoke_at_safepoint(_objs);
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481 }
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482 }
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483
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484 BiasedLocking::Condition status_code() const {
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485 return _status_code;
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486 }
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487 };
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488
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489
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490 class VM_BulkRevokeBias : public VM_RevokeBias {
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491 private:
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492 bool _bulk_rebias;
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493 bool _attempt_rebias_of_object;
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494
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495 public:
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496 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
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497 bool bulk_rebias,
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498 bool attempt_rebias_of_object)
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499 : VM_RevokeBias(obj, requesting_thread)
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500 , _bulk_rebias(bulk_rebias)
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501 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
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502
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503 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
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504 virtual bool doit_prologue() { return true; }
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505
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506 virtual void doit() {
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507 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
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508 clean_up_cached_monitor_info();
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509 }
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510 };
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511
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512
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513 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
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514 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
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515
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516 // We can revoke the biases of anonymously-biased objects
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517 // efficiently enough that we should not cause these revocations to
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518 // update the heuristics because doing so may cause unwanted bulk
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519 // revocations (which are expensive) to occur.
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520 markOop mark = obj->mark();
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521 if (mark->is_biased_anonymously() && !attempt_rebias) {
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522 // We are probably trying to revoke the bias of this object due to
|
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523 // an identity hash code computation. Try to revoke the bias
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524 // without a safepoint. This is possible if we can successfully
|
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525 // compare-and-exchange an unbiased header into the mark word of
|
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526 // the object, meaning that no other thread has raced to acquire
|
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527 // the bias of the object.
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528 markOop biased_value = mark;
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529 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
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530 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
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531 if (res_mark == biased_value) {
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532 return BIAS_REVOKED;
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533 }
|
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534 } else if (mark->has_bias_pattern()) {
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535 Klass* k = Klass::cast(obj->klass());
|
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536 markOop prototype_header = k->prototype_header();
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537 if (!prototype_header->has_bias_pattern()) {
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|
538 // This object has a stale bias from before the bulk revocation
|
|
539 // for this data type occurred. It's pointless to update the
|
|
540 // heuristics at this point so simply update the header with a
|
|
541 // CAS. If we fail this race, the object's bias has been revoked
|
|
542 // by another thread so we simply return and let the caller deal
|
|
543 // with it.
|
|
544 markOop biased_value = mark;
|
|
545 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark);
|
|
546 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
|
|
547 return BIAS_REVOKED;
|
|
548 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
|
|
549 // The epoch of this biasing has expired indicating that the
|
|
550 // object is effectively unbiased. Depending on whether we need
|
|
551 // to rebias or revoke the bias of this object we can do it
|
|
552 // efficiently enough with a CAS that we shouldn't update the
|
|
553 // heuristics. This is normally done in the assembly code but we
|
|
554 // can reach this point due to various points in the runtime
|
|
555 // needing to revoke biases.
|
|
556 if (attempt_rebias) {
|
|
557 assert(THREAD->is_Java_thread(), "");
|
|
558 markOop biased_value = mark;
|
|
559 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
|
|
560 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark);
|
|
561 if (res_mark == biased_value) {
|
|
562 return BIAS_REVOKED_AND_REBIASED;
|
|
563 }
|
|
564 } else {
|
|
565 markOop biased_value = mark;
|
|
566 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
|
|
567 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark);
|
|
568 if (res_mark == biased_value) {
|
|
569 return BIAS_REVOKED;
|
|
570 }
|
|
571 }
|
|
572 }
|
|
573 }
|
|
574
|
|
575 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
|
|
576 if (heuristics == HR_NOT_BIASED) {
|
|
577 return NOT_BIASED;
|
|
578 } else if (heuristics == HR_SINGLE_REVOKE) {
|
|
579 if (mark->biased_locker() == THREAD) {
|
|
580 // A thread is trying to revoke the bias of an object biased
|
|
581 // toward it, again likely due to an identity hash code
|
|
582 // computation. We can again avoid a safepoint in this case
|
|
583 // since we are only going to walk our own stack. There are no
|
|
584 // races with revocations occurring in other threads because we
|
|
585 // reach no safepoints in the revocation path.
|
|
586 ResourceMark rm;
|
|
587 if (TraceBiasedLocking) {
|
|
588 tty->print_cr("Revoking bias by walking my own stack:");
|
|
589 }
|
|
590 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
|
|
591 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
|
|
592 assert(cond == BIAS_REVOKED, "why not?");
|
|
593 return cond;
|
|
594 } else {
|
|
595 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
|
|
596 VMThread::execute(&revoke);
|
|
597 return revoke.status_code();
|
|
598 }
|
|
599 }
|
|
600
|
|
601 assert((heuristics == HR_BULK_REVOKE) ||
|
|
602 (heuristics == HR_BULK_REBIAS), "?");
|
|
603 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
|
|
604 (heuristics == HR_BULK_REBIAS),
|
|
605 attempt_rebias);
|
|
606 VMThread::execute(&bulk_revoke);
|
|
607 return bulk_revoke.status_code();
|
|
608 }
|
|
609
|
|
610
|
|
611 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
|
|
612 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
|
|
613 if (objs->length() == 0) {
|
|
614 return;
|
|
615 }
|
|
616 VM_RevokeBias revoke(objs, JavaThread::current());
|
|
617 VMThread::execute(&revoke);
|
|
618 }
|
|
619
|
|
620
|
|
621 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
|
|
622 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
|
|
623 oop obj = h_obj();
|
|
624 HeuristicsResult heuristics = update_heuristics(obj, false);
|
|
625 if (heuristics == HR_SINGLE_REVOKE) {
|
|
626 revoke_bias(obj, false, false, NULL);
|
|
627 } else if ((heuristics == HR_BULK_REBIAS) ||
|
|
628 (heuristics == HR_BULK_REVOKE)) {
|
|
629 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
|
|
630 }
|
|
631 clean_up_cached_monitor_info();
|
|
632 }
|
|
633
|
|
634
|
|
635 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
|
|
636 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
|
|
637 int len = objs->length();
|
|
638 for (int i = 0; i < len; i++) {
|
|
639 oop obj = (objs->at(i))();
|
|
640 HeuristicsResult heuristics = update_heuristics(obj, false);
|
|
641 if (heuristics == HR_SINGLE_REVOKE) {
|
|
642 revoke_bias(obj, false, false, NULL);
|
|
643 } else if ((heuristics == HR_BULK_REBIAS) ||
|
|
644 (heuristics == HR_BULK_REVOKE)) {
|
|
645 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
|
|
646 }
|
|
647 }
|
|
648 clean_up_cached_monitor_info();
|
|
649 }
|
|
650
|
|
651
|
|
652 void BiasedLocking::preserve_marks() {
|
|
653 if (!UseBiasedLocking)
|
|
654 return;
|
|
655
|
|
656 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
|
|
657
|
|
658 assert(_preserved_oop_stack == NULL, "double initialization");
|
|
659 assert(_preserved_mark_stack == NULL, "double initialization");
|
|
660
|
|
661 // In order to reduce the number of mark words preserved during GC
|
|
662 // due to the presence of biased locking, we reinitialize most mark
|
|
663 // words to the class's prototype during GC -- even those which have
|
|
664 // a currently valid bias owner. One important situation where we
|
|
665 // must not clobber a bias is when a biased object is currently
|
|
666 // locked. To handle this case we iterate over the currently-locked
|
|
667 // monitors in a prepass and, if they are biased, preserve their
|
|
668 // mark words here. This should be a relatively small set of objects
|
|
669 // especially compared to the number of objects in the heap.
|
|
670 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true);
|
|
671 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true);
|
|
672
|
|
673 ResourceMark rm;
|
|
674 Thread* cur = Thread::current();
|
|
675 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
|
|
676 if (thread->has_last_Java_frame()) {
|
|
677 RegisterMap rm(thread);
|
|
678 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
|
|
679 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
|
|
680 if (monitors != NULL) {
|
|
681 int len = monitors->length();
|
|
682 // Walk monitors youngest to oldest
|
|
683 for (int i = len - 1; i >= 0; i--) {
|
|
684 MonitorInfo* mon_info = monitors->at(i);
|
|
685 oop owner = mon_info->owner();
|
|
686 if (owner != NULL) {
|
|
687 markOop mark = owner->mark();
|
|
688 if (mark->has_bias_pattern()) {
|
|
689 _preserved_oop_stack->push(Handle(cur, owner));
|
|
690 _preserved_mark_stack->push(mark);
|
|
691 }
|
|
692 }
|
|
693 }
|
|
694 }
|
|
695 }
|
|
696 }
|
|
697 }
|
|
698 }
|
|
699
|
|
700
|
|
701 void BiasedLocking::restore_marks() {
|
|
702 if (!UseBiasedLocking)
|
|
703 return;
|
|
704
|
|
705 assert(_preserved_oop_stack != NULL, "double free");
|
|
706 assert(_preserved_mark_stack != NULL, "double free");
|
|
707
|
|
708 int len = _preserved_oop_stack->length();
|
|
709 for (int i = 0; i < len; i++) {
|
|
710 Handle owner = _preserved_oop_stack->at(i);
|
|
711 markOop mark = _preserved_mark_stack->at(i);
|
|
712 owner->set_mark(mark);
|
|
713 }
|
|
714
|
|
715 delete _preserved_oop_stack;
|
|
716 _preserved_oop_stack = NULL;
|
|
717 delete _preserved_mark_stack;
|
|
718 _preserved_mark_stack = NULL;
|
|
719 }
|
|
720
|
|
721
|
|
722 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
|
|
723 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
|
|
724 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
|
|
725 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
|
|
726 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
|
|
727 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
|
|
728 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
|
|
729
|
|
730
|
|
731 // BiasedLockingCounters
|
|
732
|
|
733 int BiasedLockingCounters::slow_path_entry_count() {
|
|
734 if (_slow_path_entry_count != 0) {
|
|
735 return _slow_path_entry_count;
|
|
736 }
|
|
737 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
|
|
738 _rebiased_lock_entry_count + _revoked_lock_entry_count +
|
|
739 _fast_path_entry_count;
|
|
740
|
|
741 return _total_entry_count - sum;
|
|
742 }
|
|
743
|
|
744 void BiasedLockingCounters::print_on(outputStream* st) {
|
|
745 tty->print_cr("# total entries: %d", _total_entry_count);
|
|
746 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
|
|
747 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
|
|
748 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
|
|
749 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
|
|
750 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
|
|
751 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
|
|
752 }
|