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annotate src/thread/dc/SDL_syscond.c @ 3070:3e3724fb829e

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Fixed bug #681 Description From Philipp 2009-01-16 20:50:01 (-) [reply] The File test/README from the svn says this: testgl A very simple example of using OpenGL with SDL testgl2 Improved version of testgl It is actually exchanged. testgl.c is the improved version right now and testgl2.c the simple one.
author Sam Lantinga <slouken@libsdl.org>
date Tue, 17 Feb 2009 05:44:49 +0000
parents 99210400e8b9
children
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2009 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 #include "SDL_config.h"
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23
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24 /* An implementation of condition variables using semaphores and mutexes */
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25 /*
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26 This implementation borrows heavily from the BeOS condition variable
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27 implementation, written by Christopher Tate and Owen Smith. Thanks!
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28 */
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29
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30 #include "SDL_thread.h"
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31
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32 struct SDL_cond
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33 {
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34 SDL_mutex *lock;
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35 int waiting;
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36 int signals;
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37 SDL_sem *wait_sem;
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38 SDL_sem *wait_done;
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39 };
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40
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41 /* Create a condition variable */
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42 SDL_cond *
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43 SDL_CreateCond(void)
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44 {
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45 SDL_cond *cond;
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46
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47 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
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48 if (cond) {
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49 cond->lock = SDL_CreateMutex();
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50 cond->wait_sem = SDL_CreateSemaphore(0);
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51 cond->wait_done = SDL_CreateSemaphore(0);
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52 cond->waiting = cond->signals = 0;
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53 if (!cond->lock || !cond->wait_sem || !cond->wait_done) {
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54 SDL_DestroyCond(cond);
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55 cond = NULL;
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56 }
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57 } else {
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58 SDL_OutOfMemory();
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59 }
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60 return (cond);
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61 }
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62
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63 /* Destroy a condition variable */
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64 void
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65 SDL_DestroyCond(SDL_cond * cond)
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66 {
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67 if (cond) {
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68 if (cond->wait_sem) {
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69 SDL_DestroySemaphore(cond->wait_sem);
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70 }
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71 if (cond->wait_done) {
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72 SDL_DestroySemaphore(cond->wait_done);
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73 }
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74 if (cond->lock) {
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75 SDL_DestroyMutex(cond->lock);
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76 }
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77 SDL_free(cond);
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78 }
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79 }
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80
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81 /* Restart one of the threads that are waiting on the condition variable */
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82 int
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83 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
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108 SDL_CondBroadcast(SDL_cond * cond)
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109 {
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110 if (!cond) {
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111 SDL_SetError("Passed a NULL condition variable");
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112 return -1;
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113 }
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114
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115 /* If there are waiting threads not already signalled, then
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116 signal the condition and wait for the thread to respond.
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117 */
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118 SDL_LockMutex(cond->lock);
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119 if (cond->waiting > cond->signals) {
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120 int i, num_waiting;
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121
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122 num_waiting = (cond->waiting - cond->signals);
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123 cond->signals = cond->waiting;
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124 for (i = 0; i < num_waiting; ++i) {
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125 SDL_SemPost(cond->wait_sem);
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126 }
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127 /* Now all released threads are blocked here, waiting for us.
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128 Collect them all (and win fabulous prizes!) :-)
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129 */
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130 SDL_UnlockMutex(cond->lock);
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131 for (i = 0; i < num_waiting; ++i) {
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132 SDL_SemWait(cond->wait_done);
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133 }
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134 } else {
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135 SDL_UnlockMutex(cond->lock);
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136 }
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137
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138 return 0;
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139 }
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140
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141 /* Wait on the condition variable for at most 'ms' milliseconds.
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142 The mutex must be locked before entering this function!
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143 The mutex is unlocked during the wait, and locked again after the wait.
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144
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145 Typical use:
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146
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147 Thread A:
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148 SDL_LockMutex(lock);
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149 while ( ! condition ) {
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150 SDL_CondWait(cond);
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151 }
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152 SDL_UnlockMutex(lock);
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153
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154 Thread B:
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155 SDL_LockMutex(lock);
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156 ...
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157 condition = true;
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158 ...
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159 SDL_UnlockMutex(lock);
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160 */
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161 int
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162 SDL_CondWaitTimeout(SDL_cond * cond, SDL_mutex * mutex, Uint32 ms)
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163 {
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164 int retval;
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165
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166 if (!cond) {
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167 SDL_SetError("Passed a NULL condition variable");
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168 return -1;
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169 }
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170
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171 /* Obtain the protection mutex, and increment the number of waiters.
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172 This allows the signal mechanism to only perform a signal if there
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173 are waiting threads.
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174 */
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175 SDL_LockMutex(cond->lock);
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176 ++cond->waiting;
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177 SDL_UnlockMutex(cond->lock);
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178
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179 /* Unlock the mutex, as is required by condition variable semantics */
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180 SDL_UnlockMutex(mutex);
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181
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182 /* Wait for a signal */
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183 if (ms == SDL_MUTEX_MAXWAIT) {
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184 retval = SDL_SemWait(cond->wait_sem);
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185 } else {
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186 retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
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187 }
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188
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189 /* Let the signaler know we have completed the wait, otherwise
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190 the signaler can race ahead and get the condition semaphore
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191 if we are stopped between the mutex unlock and semaphore wait,
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192 giving a deadlock. See the following URL for details:
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193 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
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194 */
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195 SDL_LockMutex(cond->lock);
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196 if (cond->signals > 0) {
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197 /* If we timed out, we need to eat a condition signal */
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198 if (retval > 0) {
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199 SDL_SemWait(cond->wait_sem);
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200 }
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201 /* We always notify the signal thread that we are done */
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202 SDL_SemPost(cond->wait_done);
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203
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204 /* Signal handshake complete */
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205 --cond->signals;
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206 }
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207 --cond->waiting;
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208 SDL_UnlockMutex(cond->lock);
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209
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210 /* Lock the mutex, as is required by condition variable semantics */
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211 SDL_LockMutex(mutex);
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212
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213 return retval;
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214 }
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215
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216 /* Wait on the condition variable forever */
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217 int
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218 SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex)
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219 {
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220 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
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221 }
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222
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223 /* vi: set ts=4 sw=4 expandtab: */