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annotate src/thread/dc/SDL_syscond.c @ 1361:19418e4422cb

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New configure-based build system. Still work in progress, but much improved
author Sam Lantinga <slouken@libsdl.org>
date Thu, 16 Feb 2006 10:11:48 +0000
parents c71e05b4dc2e
children d910939febfa
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 "SDL_thread.h"
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30
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31 struct SDL_cond
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32 {
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33 SDL_mutex *lock;
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34 int waiting;
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35 int signals;
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36 SDL_sem *wait_sem;
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37 SDL_sem *wait_done;
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38 };
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39
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40 /* Create a condition variable */
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41 SDL_cond * SDL_CreateCond(void)
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42 {
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43 SDL_cond *cond;
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44
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45 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
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46 if ( cond ) {
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47 cond->lock = SDL_CreateMutex();
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48 cond->wait_sem = SDL_CreateSemaphore(0);
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49 cond->wait_done = SDL_CreateSemaphore(0);
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50 cond->waiting = cond->signals = 0;
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51 if ( ! cond->lock || ! cond->wait_sem || ! cond->wait_done ) {
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52 SDL_DestroyCond(cond);
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53 cond = NULL;
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54 }
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55 } else {
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56 SDL_OutOfMemory();
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57 }
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58 return(cond);
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59 }
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60
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61 /* Destroy a condition variable */
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62 void SDL_DestroyCond(SDL_cond *cond)
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63 {
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64 if ( cond ) {
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65 if ( cond->wait_sem ) {
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66 SDL_DestroySemaphore(cond->wait_sem);
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67 }
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68 if ( cond->wait_done ) {
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69 SDL_DestroySemaphore(cond->wait_done);
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70 }
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71 if ( cond->lock ) {
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72 SDL_DestroyMutex(cond->lock);
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73 }
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74 SDL_free(cond);
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75 }
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76 }
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77
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78 /* Restart one of the threads that are waiting on the condition variable */
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79 int SDL_CondSignal(SDL_cond *cond)
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80 {
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81 if ( ! cond ) {
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82 SDL_SetError("Passed a NULL condition variable");
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83 return -1;
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84 }
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85
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86 /* If there are waiting threads not already signalled, then
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87 signal the condition and wait for the thread to respond.
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88 */
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89 SDL_LockMutex(cond->lock);
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90 if ( cond->waiting > cond->signals ) {
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91 ++cond->signals;
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92 SDL_SemPost(cond->wait_sem);
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93 SDL_UnlockMutex(cond->lock);
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94 SDL_SemWait(cond->wait_done);
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95 } else {
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96 SDL_UnlockMutex(cond->lock);
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97 }
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98
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99 return 0;
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100 }
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101
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102 /* Restart all threads that are waiting on the condition variable */
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103 int SDL_CondBroadcast(SDL_cond *cond)
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104 {
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105 if ( ! cond ) {
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106 SDL_SetError("Passed a NULL condition variable");
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107 return -1;
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108 }
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109
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110 /* If there are waiting threads not already signalled, then
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111 signal the condition and wait for the thread to respond.
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112 */
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113 SDL_LockMutex(cond->lock);
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114 if ( cond->waiting > cond->signals ) {
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115 int i, num_waiting;
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116
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117 num_waiting = (cond->waiting - cond->signals);
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118 cond->signals = cond->waiting;
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119 for ( i=0; i<num_waiting; ++i ) {
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120 SDL_SemPost(cond->wait_sem);
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121 }
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122 /* Now all released threads are blocked here, waiting for us.
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123 Collect them all (and win fabulous prizes!) :-)
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124 */
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125 SDL_UnlockMutex(cond->lock);
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126 for ( i=0; i<num_waiting; ++i ) {
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127 SDL_SemWait(cond->wait_done);
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128 }
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129 } else {
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130 SDL_UnlockMutex(cond->lock);
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131 }
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132
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133 return 0;
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134 }
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135
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136 /* Wait on the condition variable for at most 'ms' milliseconds.
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137 The mutex must be locked before entering this function!
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138 The mutex is unlocked during the wait, and locked again after the wait.
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139
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140 Typical use:
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141
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142 Thread A:
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143 SDL_LockMutex(lock);
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144 while ( ! condition ) {
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145 SDL_CondWait(cond);
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146 }
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147 SDL_UnlockMutex(lock);
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148
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149 Thread B:
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150 SDL_LockMutex(lock);
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151 ...
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152 condition = true;
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153 ...
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154 SDL_UnlockMutex(lock);
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155 */
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156 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
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157 {
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158 int retval;
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159
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160 if ( ! cond ) {
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161 SDL_SetError("Passed a NULL condition variable");
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162 return -1;
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163 }
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164
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165 /* Obtain the protection mutex, and increment the number of waiters.
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166 This allows the signal mechanism to only perform a signal if there
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167 are waiting threads.
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168 */
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169 SDL_LockMutex(cond->lock);
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170 ++cond->waiting;
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171 SDL_UnlockMutex(cond->lock);
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172
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173 /* Unlock the mutex, as is required by condition variable semantics */
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174 SDL_UnlockMutex(mutex);
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175
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176 /* Wait for a signal */
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177 if ( ms == SDL_MUTEX_MAXWAIT ) {
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178 retval = SDL_SemWait(cond->wait_sem);
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179 } else {
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180 retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
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181 }
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182
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183 /* Let the signaler know we have completed the wait, otherwise
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184 the signaler can race ahead and get the condition semaphore
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185 if we are stopped between the mutex unlock and semaphore wait,
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186 giving a deadlock. See the following URL for details:
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187 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
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188 */
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189 SDL_LockMutex(cond->lock);
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190 if ( cond->signals > 0 ) {
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191 /* If we timed out, we need to eat a condition signal */
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192 if ( retval > 0 ) {
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193 SDL_SemWait(cond->wait_sem);
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194 }
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195 /* We always notify the signal thread that we are done */
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196 SDL_SemPost(cond->wait_done);
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197
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198 /* Signal handshake complete */
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199 --cond->signals;
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200 }
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201 --cond->waiting;
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202 SDL_UnlockMutex(cond->lock);
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203
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204 /* Lock the mutex, as is required by condition variable semantics */
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205 SDL_LockMutex(mutex);
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206
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207 return retval;
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208 }
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209
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210 /* Wait on the condition variable forever */
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211 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
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212 {
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213 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
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214 }