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1 /*
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2 * Copyright 2001 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 <stdio.h>
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26 #include <assert.h>
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27 #include "Monitor.hpp"
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28
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29 Monitor::Monitor() {
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30 _lock_count = -1; // No threads have entered the critical section
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31 _owner = NULL;
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32 _lock_event = CreateEvent(NULL, false, false, NULL);
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33 _wait_event = CreateEvent(NULL, true, false, NULL);
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34 _counter = 0;
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35 _tickets = 0;
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36 _waiters = 0;
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37 }
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38
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39 Monitor::~Monitor() {
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40 assert(_owner == NULL); // Otherwise, owned monitor being deleted
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41 assert(_lock_count == -1); // Otherwise, monitor being deleted with non -1 lock count
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42 CloseHandle(_lock_event);
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43 CloseHandle(_wait_event);
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44 }
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45
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46 void
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47 Monitor::lock() {
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48 if (InterlockedIncrement(&_lock_count) == 0) {
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49 // Success, we now own the lock
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50 } else {
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51 DWORD dwRet = WaitForSingleObject((HANDLE)_lock_event, INFINITE);
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52 assert(dwRet == WAIT_OBJECT_0); // Unexpected return value from WaitForSingleObject
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53 }
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54 assert(owner() == NULL); // Otherwise, lock count and owner are inconsistent
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55 setOwner(GetCurrentThread());
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56 }
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57
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58 void
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59 Monitor::unlock() {
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60 setOwner(NULL);
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61 if (InterlockedDecrement(&_lock_count) >= 0) {
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62 // Wake a waiting thread up
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63 DWORD dwRet = SetEvent(_lock_event);
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64 assert(dwRet != 0); // Unexpected return value from SetEvent
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65 }
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66 }
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67
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68 bool
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69 Monitor::wait(long timeout) {
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70 assert(owner() != NULL);
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71 assert(owner() == GetCurrentThread());
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72
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73 // 0 means forever. Convert to Windows specific code.
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74 DWORD timeout_value = (timeout == 0) ? INFINITE : timeout;
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75 DWORD which;
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76
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77 long c = _counter;
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78 bool retry = false;
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79
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80 _waiters++;
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81 // Loop until condition variable is signaled. The event object is
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82 // set whenever the condition variable is signaled, and tickets will
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83 // reflect the number of threads which have been notified. The counter
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84 // field is used to make sure we don't respond to notifications that
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85 // have occurred *before* we started waiting, and is incremented each
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86 // time the condition variable is signaled.
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87
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88 while (true) {
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89
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90 // Leave critical region
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91 unlock();
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92
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93 // If this is a retry, let other low-priority threads have a chance
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94 // to run. Make sure that we sleep outside of the critical section.
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95 if (retry) {
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96 Sleep(1);
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97 } else {
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98 retry = true;
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99 }
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100
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101 which = WaitForSingleObject(_wait_event, timeout_value);
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102 // Enter critical section
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103 lock();
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104
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105 if (_tickets != 0 && _counter != c) break;
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106
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107 if (which == WAIT_TIMEOUT) {
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108 --_waiters;
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109 return true;
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110 }
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111 }
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112 _waiters--;
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113
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114 // If this was the last thread to be notified, then we need to reset
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115 // the event object.
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116 if (--_tickets == 0) {
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117 ResetEvent(_wait_event);
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118 }
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119
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120 return false;
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121 }
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122
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123 // Notify a single thread waiting on this monitor
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124 bool
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125 Monitor::notify() {
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126 assert(ownedBySelf()); // Otherwise, notify on unknown thread
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127
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128 if (_waiters > _tickets) {
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129 if (!SetEvent(_wait_event)) {
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130 return false;
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131 }
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132 _tickets++;
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133 _counter++;
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134 }
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135
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136 return true;
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137 }
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138
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139 // Notify all threads waiting on this monitor
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140 bool
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141 Monitor::notifyAll() {
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142 assert(ownedBySelf()); // Otherwise, notifyAll on unknown thread
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143
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144 if (_waiters > 0) {
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145 if (!SetEvent(_wait_event)) {
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146 return false;
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147 }
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148 _tickets = _waiters;
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149 _counter++;
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150 }
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151
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152 return true;
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153 }
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154
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155 HANDLE
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156 Monitor::owner() {
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157 return _owner;
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158 }
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159
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160 void
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161 Monitor::setOwner(HANDLE owner) {
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162 if (owner != NULL) {
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163 assert(_owner == NULL); // Setting owner thread of already owned monitor
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164 assert(owner == GetCurrentThread()); // Else should not be doing this
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165 } else {
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166 HANDLE oldOwner = _owner;
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167 assert(oldOwner != NULL); // Removing the owner thread of an unowned mutex
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168 assert(oldOwner == GetCurrentThread());
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169 }
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170 _owner = owner;
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171 }
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172
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173 bool
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174 Monitor::ownedBySelf() {
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175 return (_owner == GetCurrentThread());
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176 }
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