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annotate src/thread/dc/SDL_syscond.c @ 1312:c9b51268668f

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Updated copyright information and removed rcs id lines (problematic in branch merges) I batch edited these files, so please let me know if I've accidentally removed anybody's credit here.
author Sam Lantinga <slouken@libsdl.org>
date Wed, 01 Feb 2006 06:32:25 +0000
parents b8d311d90021
children 3692456e7b0f
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2006 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22
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23 /* An implementation of condition variables using semaphores and mutexes */
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24 /*
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25 This implementation borrows heavily from the BeOS condition variable
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26 implementation, written by Christopher Tate and Owen Smith. Thanks!
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27 */
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28
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29 #include <stdio.h>
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30 #include <stdlib.h>
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31
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32 #include "SDL_error.h"
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33 #include "SDL_thread.h"
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34
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35 struct SDL_cond
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36 {
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37 SDL_mutex *lock;
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38 int waiting;
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39 int signals;
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40 SDL_sem *wait_sem;
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41 SDL_sem *wait_done;
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42 };
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43
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44 /* Create a condition variable */
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45 SDL_cond * SDL_CreateCond(void)
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46 {
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47 SDL_cond *cond;
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48
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49 cond = (SDL_cond *) malloc(sizeof(SDL_cond));
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50 if ( cond ) {
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51 cond->lock = SDL_CreateMutex();
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52 cond->wait_sem = SDL_CreateSemaphore(0);
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53 cond->wait_done = SDL_CreateSemaphore(0);
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54 cond->waiting = cond->signals = 0;
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55 if ( ! cond->lock || ! cond->wait_sem || ! cond->wait_done ) {
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56 SDL_DestroyCond(cond);
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57 cond = NULL;
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58 }
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59 } else {
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60 SDL_OutOfMemory();
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61 }
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62 return(cond);
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63 }
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64
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65 /* Destroy a condition variable */
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66 void SDL_DestroyCond(SDL_cond *cond)
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67 {
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68 if ( cond ) {
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69 if ( cond->wait_sem ) {
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70 SDL_DestroySemaphore(cond->wait_sem);
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71 }
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72 if ( cond->wait_done ) {
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73 SDL_DestroySemaphore(cond->wait_done);
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74 }
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75 if ( cond->lock ) {
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76 SDL_DestroyMutex(cond->lock);
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77 }
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78 free(cond);
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79 }
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80 }
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81
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82 /* Restart one of the threads that are waiting on the condition variable */
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83 int SDL_CondSignal(SDL_cond *cond)
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84 {
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85 if ( ! cond ) {
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86 SDL_SetError("Passed a NULL condition variable");
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87 return -1;
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88 }
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89
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90 /* If there are waiting threads not already signalled, then
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91 signal the condition and wait for the thread to respond.
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92 */
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93 SDL_LockMutex(cond->lock);
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94 if ( cond->waiting > cond->signals ) {
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95 ++cond->signals;
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96 SDL_SemPost(cond->wait_sem);
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97 SDL_UnlockMutex(cond->lock);
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98 SDL_SemWait(cond->wait_done);
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99 } else {
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100 SDL_UnlockMutex(cond->lock);
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101 }
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102
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103 return 0;
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104 }
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105
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106 /* Restart all threads that are waiting on the condition variable */
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107 int SDL_CondBroadcast(SDL_cond *cond)
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108 {
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109 if ( ! cond ) {
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110 SDL_SetError("Passed a NULL condition variable");
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111 return -1;
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112 }
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113
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114 /* If there are waiting threads not already signalled, then
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115 signal the condition and wait for the thread to respond.
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116 */
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117 SDL_LockMutex(cond->lock);
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118 if ( cond->waiting > cond->signals ) {
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119 int i, num_waiting;
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120
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121 num_waiting = (cond->waiting - cond->signals);
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122 cond->signals = cond->waiting;
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123 for ( i=0; i<num_waiting; ++i ) {
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124 SDL_SemPost(cond->wait_sem);
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125 }
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126 /* Now all released threads are blocked here, waiting for us.
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127 Collect them all (and win fabulous prizes!) :-)
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128 */
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129 SDL_UnlockMutex(cond->lock);
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130 for ( i=0; i<num_waiting; ++i ) {
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131 SDL_SemWait(cond->wait_done);
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132 }
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133 } else {
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134 SDL_UnlockMutex(cond->lock);
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135 }
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136
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137 return 0;
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138 }
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139
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140 /* Wait on the condition variable for at most 'ms' milliseconds.
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141 The mutex must be locked before entering this function!
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142 The mutex is unlocked during the wait, and locked again after the wait.
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143
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144 Typical use:
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145
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146 Thread A:
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147 SDL_LockMutex(lock);
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148 while ( ! condition ) {
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149 SDL_CondWait(cond);
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150 }
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151 SDL_UnlockMutex(lock);
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152
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153 Thread B:
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154 SDL_LockMutex(lock);
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155 ...
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156 condition = true;
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157 ...
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158 SDL_UnlockMutex(lock);
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159 */
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160 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
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161 {
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162 int retval;
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163
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164 if ( ! cond ) {
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165 SDL_SetError("Passed a NULL condition variable");
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166 return -1;
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167 }
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168
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169 /* Obtain the protection mutex, and increment the number of waiters.
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170 This allows the signal mechanism to only perform a signal if there
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171 are waiting threads.
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172 */
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173 SDL_LockMutex(cond->lock);
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174 ++cond->waiting;
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175 SDL_UnlockMutex(cond->lock);
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176
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177 /* Unlock the mutex, as is required by condition variable semantics */
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178 SDL_UnlockMutex(mutex);
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179
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180 /* Wait for a signal */
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181 if ( ms == SDL_MUTEX_MAXWAIT ) {
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182 retval = SDL_SemWait(cond->wait_sem);
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183 } else {
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184 retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
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185 }
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186
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187 /* Let the signaler know we have completed the wait, otherwise
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188 the signaler can race ahead and get the condition semaphore
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189 if we are stopped between the mutex unlock and semaphore wait,
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190 giving a deadlock. See the following URL for details:
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191 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
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192 */
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193 SDL_LockMutex(cond->lock);
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194 if ( cond->signals > 0 ) {
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195 /* If we timed out, we need to eat a condition signal */
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196 if ( retval > 0 ) {
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197 SDL_SemWait(cond->wait_sem);
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198 }
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199 /* We always notify the signal thread that we are done */
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200 SDL_SemPost(cond->wait_done);
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201
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202 /* Signal handshake complete */
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203 --cond->signals;
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204 }
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205 --cond->waiting;
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206 SDL_UnlockMutex(cond->lock);
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207
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208 /* Lock the mutex, as is required by condition variable semantics */
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209 SDL_LockMutex(mutex);
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210
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211 return retval;
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212 }
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213
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214 /* Wait on the condition variable forever */
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215 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
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216 {
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217 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
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218 }