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annotate src/thread/dc/SDL_syscond.c @ 1338:604d73db6802

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Removed uses of stdlib.h and string.h
author Sam Lantinga <slouken@libsdl.org>
date Tue, 07 Feb 2006 09:29:18 +0000
parents 3692456e7b0f
children c71e05b4dc2e
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_stdlib.h"
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30 #include "SDL_error.h"
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31 #include "SDL_thread.h"
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32
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33 struct SDL_cond
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34 {
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35 SDL_mutex *lock;
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36 int waiting;
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37 int signals;
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38 SDL_sem *wait_sem;
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39 SDL_sem *wait_done;
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40 };
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41
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42 /* Create a condition variable */
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43 SDL_cond * 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 SDL_DestroyCond(SDL_cond *cond)
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65 {
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66 if ( cond ) {
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67 if ( cond->wait_sem ) {
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68 SDL_DestroySemaphore(cond->wait_sem);
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69 }
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70 if ( cond->wait_done ) {
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71 SDL_DestroySemaphore(cond->wait_done);
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72 }
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73 if ( cond->lock ) {
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74 SDL_DestroyMutex(cond->lock);
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75 }
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76 SDL_free(cond);
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77 }
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78 }
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79
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80 /* Restart one of the threads that are waiting on the condition variable */
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81 int SDL_CondSignal(SDL_cond *cond)
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82 {
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83 if ( ! cond ) {
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84 SDL_SetError("Passed a NULL condition variable");
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85 return -1;
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86 }
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87
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88 /* If there are waiting threads not already signalled, then
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89 signal the condition and wait for the thread to respond.
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90 */
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91 SDL_LockMutex(cond->lock);
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92 if ( cond->waiting > cond->signals ) {
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93 ++cond->signals;
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94 SDL_SemPost(cond->wait_sem);
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95 SDL_UnlockMutex(cond->lock);
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96 SDL_SemWait(cond->wait_done);
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97 } else {
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98 SDL_UnlockMutex(cond->lock);
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99 }
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100
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101 return 0;
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102 }
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103
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104 /* Restart all threads that are waiting on the condition variable */
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105 int SDL_CondBroadcast(SDL_cond *cond)
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106 {
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107 if ( ! cond ) {
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108 SDL_SetError("Passed a NULL condition variable");
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109 return -1;
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110 }
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111
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112 /* If there are waiting threads not already signalled, then
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113 signal the condition and wait for the thread to respond.
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114 */
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115 SDL_LockMutex(cond->lock);
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116 if ( cond->waiting > cond->signals ) {
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117 int i, num_waiting;
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118
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119 num_waiting = (cond->waiting - cond->signals);
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120 cond->signals = cond->waiting;
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121 for ( i=0; i<num_waiting; ++i ) {
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122 SDL_SemPost(cond->wait_sem);
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123 }
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124 /* Now all released threads are blocked here, waiting for us.
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125 Collect them all (and win fabulous prizes!) :-)
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126 */
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127 SDL_UnlockMutex(cond->lock);
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128 for ( i=0; i<num_waiting; ++i ) {
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129 SDL_SemWait(cond->wait_done);
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130 }
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131 } else {
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132 SDL_UnlockMutex(cond->lock);
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133 }
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134
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135 return 0;
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136 }
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137
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138 /* Wait on the condition variable for at most 'ms' milliseconds.
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139 The mutex must be locked before entering this function!
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140 The mutex is unlocked during the wait, and locked again after the wait.
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141
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142 Typical use:
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143
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144 Thread A:
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145 SDL_LockMutex(lock);
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146 while ( ! condition ) {
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147 SDL_CondWait(cond);
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148 }
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149 SDL_UnlockMutex(lock);
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150
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151 Thread B:
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152 SDL_LockMutex(lock);
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153 ...
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154 condition = true;
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155 ...
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156 SDL_UnlockMutex(lock);
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157 */
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158 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
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159 {
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160 int retval;
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161
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162 if ( ! cond ) {
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163 SDL_SetError("Passed a NULL condition variable");
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164 return -1;
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165 }
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166
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167 /* Obtain the protection mutex, and increment the number of waiters.
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168 This allows the signal mechanism to only perform a signal if there
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169 are waiting threads.
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170 */
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171 SDL_LockMutex(cond->lock);
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172 ++cond->waiting;
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173 SDL_UnlockMutex(cond->lock);
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174
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175 /* Unlock the mutex, as is required by condition variable semantics */
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176 SDL_UnlockMutex(mutex);
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177
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178 /* Wait for a signal */
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179 if ( ms == SDL_MUTEX_MAXWAIT ) {
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180 retval = SDL_SemWait(cond->wait_sem);
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181 } else {
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182 retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
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183 }
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184
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185 /* Let the signaler know we have completed the wait, otherwise
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186 the signaler can race ahead and get the condition semaphore
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187 if we are stopped between the mutex unlock and semaphore wait,
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188 giving a deadlock. See the following URL for details:
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189 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
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190 */
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191 SDL_LockMutex(cond->lock);
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192 if ( cond->signals > 0 ) {
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193 /* If we timed out, we need to eat a condition signal */
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194 if ( retval > 0 ) {
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195 SDL_SemWait(cond->wait_sem);
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196 }
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197 /* We always notify the signal thread that we are done */
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198 SDL_SemPost(cond->wait_done);
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199
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200 /* Signal handshake complete */
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201 --cond->signals;
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202 }
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203 --cond->waiting;
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204 SDL_UnlockMutex(cond->lock);
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205
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206 /* Lock the mutex, as is required by condition variable semantics */
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207 SDL_LockMutex(mutex);
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208
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209 return retval;
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210 }
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211
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212 /* Wait on the condition variable forever */
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213 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
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214 {
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215 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
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216 }