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0
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1 /*
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2 * Copyright 1998-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any 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/_vmThread.cpp.incl"
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27
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28 // Dummy VM operation to act as first element in our circular double-linked list
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29 class VM_Dummy: public VM_Operation {
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30 VMOp_Type type() const { return VMOp_Dummy; }
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31 void doit() {};
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32 };
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33
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34 VMOperationQueue::VMOperationQueue() {
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35 // The queue is a circular doubled-linked list, which always contains
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36 // one element (i.e., one element means empty).
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37 for(int i = 0; i < nof_priorities; i++) {
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38 _queue_length[i] = 0;
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39 _queue_counter = 0;
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40 _queue[i] = new VM_Dummy();
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41 _queue[i]->set_next(_queue[i]);
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42 _queue[i]->set_prev(_queue[i]);
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43 }
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44 _drain_list = NULL;
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45 }
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46
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47
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48 bool VMOperationQueue::queue_empty(int prio) {
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49 // It is empty if there is exactly one element
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50 bool empty = (_queue[prio] == _queue[prio]->next());
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51 assert( (_queue_length[prio] == 0 && empty) ||
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52 (_queue_length[prio] > 0 && !empty), "sanity check");
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53 return _queue_length[prio] == 0;
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54 }
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55
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56 // Inserts an element to the right of the q element
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57 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
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58 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
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59 n->set_prev(q);
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60 n->set_next(q->next());
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61 q->next()->set_prev(n);
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62 q->set_next(n);
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63 }
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64
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65 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
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66 _queue_length[prio]++;
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67 insert(_queue[prio]->next(), op);
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68 }
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69
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70 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
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71 _queue_length[prio]++;
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72 insert(_queue[prio]->prev(), op);
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73 }
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74
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75
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76 void VMOperationQueue::unlink(VM_Operation* q) {
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77 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
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78 q->prev()->set_next(q->next());
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79 q->next()->set_prev(q->prev());
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80 }
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81
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82 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
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83 if (queue_empty(prio)) return NULL;
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84 assert(_queue_length[prio] >= 0, "sanity check");
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85 _queue_length[prio]--;
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86 VM_Operation* r = _queue[prio]->next();
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87 assert(r != _queue[prio], "cannot remove base element");
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88 unlink(r);
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89 return r;
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90 }
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91
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92 VM_Operation* VMOperationQueue::queue_drain(int prio) {
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93 if (queue_empty(prio)) return NULL;
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94 DEBUG_ONLY(int length = _queue_length[prio];);
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95 assert(length >= 0, "sanity check");
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96 _queue_length[prio] = 0;
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97 VM_Operation* r = _queue[prio]->next();
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98 assert(r != _queue[prio], "cannot remove base element");
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99 // remove links to base element from head and tail
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100 r->set_prev(NULL);
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101 _queue[prio]->prev()->set_next(NULL);
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102 // restore queue to empty state
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103 _queue[prio]->set_next(_queue[prio]);
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104 _queue[prio]->set_prev(_queue[prio]);
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105 assert(queue_empty(prio), "drain corrupted queue")
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106 #ifdef DEBUG
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107 int len = 0;
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108 VM_Operation* cur;
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109 for(cur = r; cur != NULL; cur=cur->next()) len++;
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110 assert(len == length, "drain lost some ops");
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111 #endif
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112 return r;
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113 }
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114
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115 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
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116 VM_Operation* cur = _queue[queue];
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117 cur = cur->next();
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118 while (cur != _queue[queue]) {
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119 cur->oops_do(f);
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120 cur = cur->next();
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121 }
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122 }
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123
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124 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
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125 VM_Operation* cur = _drain_list;
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126 while (cur != NULL) {
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127 cur->oops_do(f);
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128 cur = cur->next();
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129 }
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130 }
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131
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132 //-----------------------------------------------------------------
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133 // High-level interface
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134 bool VMOperationQueue::add(VM_Operation *op) {
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135 // Encapsulates VM queue policy. Currently, that
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136 // only involves putting them on the right list
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137 if (op->evaluate_at_safepoint()) {
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138 queue_add_back(SafepointPriority, op);
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139 return true;
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140 }
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141
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142 queue_add_back(MediumPriority, op);
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143 return true;
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144 }
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145
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146 VM_Operation* VMOperationQueue::remove_next() {
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147 // Assuming VMOperation queue is two-level priority queue. If there are
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148 // more than two priorities, we need a different scheduling algorithm.
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149 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
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150 "current algorithm does not work");
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151
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152 // simple counter based scheduling to prevent starvation of lower priority
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153 // queue. -- see 4390175
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154 int high_prio, low_prio;
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155 if (_queue_counter++ < 10) {
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156 high_prio = SafepointPriority;
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157 low_prio = MediumPriority;
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158 } else {
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159 _queue_counter = 0;
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160 high_prio = MediumPriority;
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161 low_prio = SafepointPriority;
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162 }
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163
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164 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
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165 }
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166
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167 void VMOperationQueue::oops_do(OopClosure* f) {
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168 for(int i = 0; i < nof_priorities; i++) {
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169 queue_oops_do(i, f);
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170 }
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171 drain_list_oops_do(f);
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172 }
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173
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174
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175 //------------------------------------------------------------------------------------------------------------------
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176 // Implementation of VMThread stuff
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177
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178 bool VMThread::_should_terminate = false;
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179 bool VMThread::_terminated = false;
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180 Monitor* VMThread::_terminate_lock = NULL;
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181 VMThread* VMThread::_vm_thread = NULL;
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182 VM_Operation* VMThread::_cur_vm_operation = NULL;
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183 VMOperationQueue* VMThread::_vm_queue = NULL;
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184 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
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185
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186
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187 void VMThread::create() {
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188 assert(vm_thread() == NULL, "we can only allocate one VMThread");
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189 _vm_thread = new VMThread();
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190
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191 // Create VM operation queue
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192 _vm_queue = new VMOperationQueue();
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193 guarantee(_vm_queue != NULL, "just checking");
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194
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195 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
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196
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197 if (UsePerfData) {
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198 // jvmstat performance counters
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199 Thread* THREAD = Thread::current();
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200 _perf_accumulated_vm_operation_time =
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201 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
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202 PerfData::U_Ticks, CHECK);
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203 }
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204 }
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205
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206
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207 VMThread::VMThread() : Thread() {
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208 // nothing to do
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209 }
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210
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211 void VMThread::destroy() {
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212 if (_vm_thread != NULL) {
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213 delete _vm_thread;
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214 _vm_thread = NULL; // VM thread is gone
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215 }
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216 }
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217
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218 void VMThread::run() {
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219 assert(this == vm_thread(), "check");
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220
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221 this->initialize_thread_local_storage();
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222 this->record_stack_base_and_size();
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223 // Notify_lock wait checks on active_handles() to rewait in
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224 // case of spurious wakeup, it should wait on the last
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225 // value set prior to the notify
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226 this->set_active_handles(JNIHandleBlock::allocate_block());
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227
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228 {
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229 MutexLocker ml(Notify_lock);
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230 Notify_lock->notify();
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231 }
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232 // Notify_lock is destroyed by Threads::create_vm()
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233
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234 int prio = (VMThreadPriority == -1)
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235 ? os::java_to_os_priority[NearMaxPriority]
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236 : VMThreadPriority;
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237 // Note that I cannot call os::set_priority because it expects Java
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238 // priorities and I am *explicitly* using OS priorities so that it's
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239 // possible to set the VM thread priority higher than any Java thread.
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240 os::set_native_priority( this, prio );
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241
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242 // Wait for VM_Operations until termination
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243 this->loop();
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244
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245 // Note the intention to exit before safepointing.
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246 // 6295565 This has the effect of waiting for any large tty
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247 // outputs to finish.
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248 if (xtty != NULL) {
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249 ttyLocker ttyl;
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250 xtty->begin_elem("destroy_vm");
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251 xtty->stamp();
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252 xtty->end_elem();
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253 assert(should_terminate(), "termination flag must be set");
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254 }
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255
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256 // 4526887 let VM thread exit at Safepoint
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257 SafepointSynchronize::begin();
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258
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259 if (VerifyBeforeExit) {
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260 HandleMark hm(VMThread::vm_thread());
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261 // Among other things, this ensures that Eden top is correct.
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262 Universe::heap()->prepare_for_verify();
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263 os::check_heap();
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264 Universe::verify(true, true); // Silent verification to not polute normal output
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265 }
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266
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267 CompileBroker::set_should_block();
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268
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269 // wait for threads (compiler threads or daemon threads) in the
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270 // _thread_in_native state to block.
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271 VM_Exit::wait_for_threads_in_native_to_block();
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272
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273 // signal other threads that VM process is gone
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274 {
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275 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
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276 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
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277 // If that happens after _terminate_lock->wait() has unset _owner
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278 // but before it actually drops the lock and waits, the notification below
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279 // may get lost and we will have a hang. To avoid this, we need to use
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280 // Mutex::lock_without_safepoint_check().
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281 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
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282 _terminated = true;
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283 _terminate_lock->notify();
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284 }
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285
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286 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
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287 // so that the VMThread deletion completes before the main thread frees
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288 // up the CodeHeap.
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289
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290 }
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291
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292
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293 // Notify the VMThread that the last non-daemon JavaThread has terminated,
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294 // and wait until operation is performed.
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295 void VMThread::wait_for_vm_thread_exit() {
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296 { MutexLocker mu(VMOperationQueue_lock);
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297 _should_terminate = true;
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298 VMOperationQueue_lock->notify();
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299 }
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300
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301 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
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302 // because this thread has been removed from the threads list. But anything
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303 // that could get blocked by Safepoint should not be used after this point,
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304 // otherwise we will hang, since there is no one can end the safepoint.
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305
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306 // Wait until VM thread is terminated
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307 // Note: it should be OK to use Terminator_lock here. But this is called
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308 // at a very delicate time (VM shutdown) and we are operating in non- VM
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309 // thread at Safepoint. It's safer to not share lock with other threads.
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310 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
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311 while(!VMThread::is_terminated()) {
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312 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
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313 }
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314 }
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315 }
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316
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317 void VMThread::print_on(outputStream* st) const {
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318 st->print("\"%s\" ", name());
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319 Thread::print_on(st);
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320 st->cr();
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321 }
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322
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323 void VMThread::evaluate_operation(VM_Operation* op) {
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324 ResourceMark rm;
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325
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326 {
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327 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
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328 op->evaluate();
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329 }
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330
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331 // Last access of info in _cur_vm_operation!
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332 bool c_heap_allocated = op->is_cheap_allocated();
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333
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334 // Mark as completed
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335 if (!op->evaluate_concurrently()) {
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336 op->calling_thread()->increment_vm_operation_completed_count();
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337 }
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338 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
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339 // since if it is stack allocated the calling thread might have deallocated
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340 if (c_heap_allocated) {
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341 delete _cur_vm_operation;
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342 }
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343 }
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344
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345
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346 void VMThread::loop() {
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347 assert(_cur_vm_operation == NULL, "no current one should be executing");
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348
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349 while(true) {
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350 VM_Operation* safepoint_ops = NULL;
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351 //
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352 // Wait for VM operation
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353 //
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354 // use no_safepoint_check to get lock without attempting to "sneak"
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355 { MutexLockerEx mu_queue(VMOperationQueue_lock,
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356 Mutex::_no_safepoint_check_flag);
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357
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358 // Look for new operation
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359 assert(_cur_vm_operation == NULL, "no current one should be executing");
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360 _cur_vm_operation = _vm_queue->remove_next();
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361
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362 // Stall time tracking code
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363 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
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364 !_cur_vm_operation->evaluate_concurrently()) {
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365 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
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366 if (stall > 0)
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367 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
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368 }
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369
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370 while (!should_terminate() && _cur_vm_operation == NULL) {
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371 // wait with a timeout to guarantee safepoints at regular intervals
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372 bool timedout =
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373 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
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374 GuaranteedSafepointInterval);
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375
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376 // Support for self destruction
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377 if ((SelfDestructTimer != 0) && !is_error_reported() &&
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378 (os::elapsedTime() > SelfDestructTimer * 60)) {
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379 tty->print_cr("VM self-destructed");
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380 exit(-1);
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381 }
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382
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383 if (timedout && (SafepointALot ||
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384 SafepointSynchronize::is_cleanup_needed())) {
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385 MutexUnlockerEx mul(VMOperationQueue_lock,
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386 Mutex::_no_safepoint_check_flag);
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387 // Force a safepoint since we have not had one for at least
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388 // 'GuaranteedSafepointInterval' milliseconds. This will run all
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389 // the clean-up processing that needs to be done regularly at a
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390 // safepoint
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391 SafepointSynchronize::begin();
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392 #ifdef ASSERT
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393 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
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394 #endif
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395 SafepointSynchronize::end();
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396 }
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397 _cur_vm_operation = _vm_queue->remove_next();
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398
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399 // If we are at a safepoint we will evaluate all the operations that
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400 // follow that also require a safepoint
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401 if (_cur_vm_operation != NULL &&
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402 _cur_vm_operation->evaluate_at_safepoint()) {
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403 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
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404 }
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405 }
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406
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407 if (should_terminate()) break;
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408 } // Release mu_queue_lock
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409
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410 //
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411 // Execute VM operation
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412 //
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413 { HandleMark hm(VMThread::vm_thread());
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414
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415 EventMark em("Executing VM operation: %s", vm_operation()->name());
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416 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
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417
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418 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
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419 // helps the VM thread to finish up the job.
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420 // FIXME: When this is enabled and there are many threads, this can degrade
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421 // performance significantly.
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422 if( VMThreadHintNoPreempt )
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423 os::hint_no_preempt();
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424
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425 // If we are at a safepoint we will evaluate all the operations that
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426 // follow that also require a safepoint
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427 if (_cur_vm_operation->evaluate_at_safepoint()) {
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428
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429 if (PrintGCApplicationConcurrentTime) {
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430 gclog_or_tty->print_cr("Application time: %3.7f seconds",
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431 RuntimeService::last_application_time_sec());
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432 }
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433
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434 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
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435
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436 SafepointSynchronize::begin();
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437 evaluate_operation(_cur_vm_operation);
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438 // now process all queued safepoint ops, iteratively draining
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439 // the queue until there are none left
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440 do {
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441 _cur_vm_operation = safepoint_ops;
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442 if (_cur_vm_operation != NULL) {
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443 do {
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444 // evaluate_operation deletes the op object so we have
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445 // to grab the next op now
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446 VM_Operation* next = _cur_vm_operation->next();
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447 _vm_queue->set_drain_list(next);
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448 evaluate_operation(_cur_vm_operation);
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449 _cur_vm_operation = next;
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450 if (PrintSafepointStatistics) {
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451 SafepointSynchronize::inc_vmop_coalesced_count();
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452 }
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453 } while (_cur_vm_operation != NULL);
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454 }
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455 // There is a chance that a thread enqueued a safepoint op
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456 // since we released the op-queue lock and initiated the safepoint.
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457 // So we drain the queue again if there is anything there, as an
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458 // optimization to try and reduce the number of safepoints.
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459 // As the safepoint synchronizes us with JavaThreads we will see
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460 // any enqueue made by a JavaThread, but the peek will not
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461 // necessarily detect a concurrent enqueue by a GC thread, but
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462 // that simply means the op will wait for the next major cycle of the
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463 // VMThread - just as it would if the GC thread lost the race for
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464 // the lock.
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465 if (_vm_queue->peek_at_safepoint_priority()) {
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466 // must hold lock while draining queue
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467 MutexLockerEx mu_queue(VMOperationQueue_lock,
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468 Mutex::_no_safepoint_check_flag);
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469 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
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470 } else {
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471 safepoint_ops = NULL;
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472 }
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473 } while(safepoint_ops != NULL);
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474
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475 _vm_queue->set_drain_list(NULL);
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476
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477 // Complete safepoint synchronization
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478 SafepointSynchronize::end();
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479
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480 if (PrintGCApplicationStoppedTime) {
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481 gclog_or_tty->print_cr("Total time for which application threads "
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482 "were stopped: %3.7f seconds",
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483 RuntimeService::last_safepoint_time_sec());
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484 }
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485
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486 } else { // not a safepoint operation
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487 if (TraceLongCompiles) {
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488 elapsedTimer t;
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489 t.start();
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490 evaluate_operation(_cur_vm_operation);
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491 t.stop();
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492 double secs = t.seconds();
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493 if (secs * 1e3 > LongCompileThreshold) {
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494 // XXX - _cur_vm_operation should not be accessed after
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495 // the completed count has been incremented; the waiting
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496 // thread may have already freed this memory.
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497 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
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498 }
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499 } else {
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500 evaluate_operation(_cur_vm_operation);
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501 }
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502
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503 _cur_vm_operation = NULL;
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504 }
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505 }
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506
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507 //
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508 // Notify (potential) waiting Java thread(s) - lock without safepoint
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509 // check so that sneaking is not possible
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510 { MutexLockerEx mu(VMOperationRequest_lock,
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511 Mutex::_no_safepoint_check_flag);
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512 VMOperationRequest_lock->notify_all();
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513 }
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514
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515 //
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516 // We want to make sure that we get to a safepoint regularly.
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517 //
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518 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
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519 long interval = SafepointSynchronize::last_non_safepoint_interval();
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520 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
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521 if (SafepointALot || max_time_exceeded) {
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522 HandleMark hm(VMThread::vm_thread());
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523 SafepointSynchronize::begin();
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524 SafepointSynchronize::end();
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525 }
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526 }
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527 }
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528 }
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529
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530 void VMThread::execute(VM_Operation* op) {
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531 Thread* t = Thread::current();
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532
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533 if (!t->is_VM_thread()) {
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534 // JavaThread or WatcherThread
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535 t->check_for_valid_safepoint_state(true);
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536
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537 // New request from Java thread, evaluate prologue
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538 if (!op->doit_prologue()) {
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539 return; // op was cancelled
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540 }
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541
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542 // Setup VM_operations for execution
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543 op->set_calling_thread(t, Thread::get_priority(t));
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544
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545 // It does not make sense to execute the epilogue, if the VM operation object is getting
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546 // deallocated by the VM thread.
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547 bool concurrent = op->evaluate_concurrently();
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548 bool execute_epilog = !op->is_cheap_allocated();
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549 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
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550
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551 // Get ticket number for non-concurrent VM operations
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552 int ticket = 0;
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553 if (!concurrent) {
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554 ticket = t->vm_operation_ticket();
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555 }
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556
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557 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
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558 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
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559 // to be queued up during a safepoint synchronization.
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560 {
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561 VMOperationQueue_lock->lock_without_safepoint_check();
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562 bool ok = _vm_queue->add(op);
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563 op->set_timestamp(os::javaTimeMillis());
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564 VMOperationQueue_lock->notify();
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565 VMOperationQueue_lock->unlock();
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566 // VM_Operation got skipped
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567 if (!ok) {
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568 assert(concurrent, "can only skip concurrent tasks");
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569 if (op->is_cheap_allocated()) delete op;
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570 return;
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571 }
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572 }
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573
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574 if (!concurrent) {
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575 // Wait for completion of request (non-concurrent)
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576 // Note: only a JavaThread triggers the safepoint check when locking
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577 MutexLocker mu(VMOperationRequest_lock);
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578 while(t->vm_operation_completed_count() < ticket) {
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579 VMOperationRequest_lock->wait(!t->is_Java_thread());
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580 }
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581 }
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582
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583 if (execute_epilog) {
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584 op->doit_epilogue();
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585 }
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586 } else {
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587 // invoked by VM thread; usually nested VM operation
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588 assert(t->is_VM_thread(), "must be a VM thread");
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589 VM_Operation* prev_vm_operation = vm_operation();
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590 if (prev_vm_operation != NULL) {
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591 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
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592 // does not allow nested scavenges or compiles.
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593 if (!prev_vm_operation->allow_nested_vm_operations()) {
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594 fatal2("Nested VM operation %s requested by operation %s", op->name(), vm_operation()->name());
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595 }
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596 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
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597 }
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598
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|
599 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
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600
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601 // Release all internal handles after operation is evaluated
|
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|
602 HandleMark hm(t);
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|
603 _cur_vm_operation = op;
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604
|
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605 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
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606 SafepointSynchronize::begin();
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607 op->evaluate();
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|
608 SafepointSynchronize::end();
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609 } else {
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|
610 op->evaluate();
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611 }
|
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612
|
|
|
613 // Free memory if needed
|
|
|
614 if (op->is_cheap_allocated()) delete op;
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|
615
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|
616 _cur_vm_operation = prev_vm_operation;
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617 }
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|
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618 }
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619
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620
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621 void VMThread::oops_do(OopClosure* f) {
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|
622 Thread::oops_do(f);
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|
623 _vm_queue->oops_do(f);
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|
624 }
|
|
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625
|
|
|
626 //------------------------------------------------------------------------------------------------------------------
|
|
|
627 #ifndef PRODUCT
|
|
|
628
|
|
|
629 void VMOperationQueue::verify_queue(int prio) {
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|
|
630 // Check that list is correctly linked
|
|
|
631 int length = _queue_length[prio];
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|
632 VM_Operation *cur = _queue[prio];
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|
633 int i;
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634
|
|
|
635 // Check forward links
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|
636 for(i = 0; i < length; i++) {
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|
637 cur = cur->next();
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|
638 assert(cur != _queue[prio], "list to short (forward)");
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|
639 }
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|
640 assert(cur->next() == _queue[prio], "list to long (forward)");
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641
|
|
|
642 // Check backwards links
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|
643 cur = _queue[prio];
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|
644 for(i = 0; i < length; i++) {
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|
|
645 cur = cur->prev();
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|
646 assert(cur != _queue[prio], "list to short (backwards)");
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|
647 }
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|
648 assert(cur->prev() == _queue[prio], "list to long (backwards)");
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|
|
649 }
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650
|
|
|
651 #endif
|
|
|
652
|
|
|
653 void VMThread::verify() {
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|
|
654 oops_do(&VerifyOopClosure::verify_oop);
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|
|
655 }
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