author | Ryan C. Gordon <icculus@icculus.org> |
Sun, 31 Mar 2013 12:48:50 -0400 | |
changeset 7037 | 3fedf1f25b94 |
parent 7009 | 161b7b6a5303 |
child 8093 | b43765095a6f |
permissions | -rw-r--r-- |
7009 | 1 |
/* |
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Simple DirectMedia Layer |
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Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org> |
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This software is provided 'as-is', without any express or implied |
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warranty. In no event will the authors be held liable for any damages |
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arising from the use of this software. |
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Permission is granted to anyone to use this software for any purpose, |
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including commercial applications, and to alter it and redistribute it |
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freely, subject to the following restrictions: |
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1. The origin of this software must not be misrepresented; you must not |
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claim that you wrote the original software. If you use this software |
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in a product, an acknowledgment in the product documentation would be |
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appreciated but is not required. |
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2. Altered source versions must be plainly marked as such, and must not be |
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misrepresented as being the original software. |
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3. This notice may not be removed or altered from any source distribution. |
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*/ |
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#include "SDL_config.h" |
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/* An implementation of condition variables using semaphores and mutexes */ |
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/* |
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This implementation borrows heavily from the BeOS condition variable |
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implementation, written by Christopher Tate and Owen Smith. Thanks! |
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*/ |
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#include "SDL_thread.h" |
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struct SDL_cond |
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{ |
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SDL_mutex *lock; |
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int waiting; |
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int signals; |
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SDL_sem *wait_sem; |
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SDL_sem *wait_done; |
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}; |
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/* Create a condition variable */ |
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SDL_cond * |
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SDL_CreateCond(void) |
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{ |
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SDL_cond *cond; |
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cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond)); |
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if (cond) { |
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cond->lock = SDL_CreateMutex(); |
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cond->wait_sem = SDL_CreateSemaphore(0); |
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cond->wait_done = SDL_CreateSemaphore(0); |
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cond->waiting = cond->signals = 0; |
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if (!cond->lock || !cond->wait_sem || !cond->wait_done) { |
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SDL_DestroyCond(cond); |
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cond = NULL; |
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} |
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} else { |
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SDL_OutOfMemory(); |
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} |
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return (cond); |
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} |
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/* Destroy a condition variable */ |
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void |
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SDL_DestroyCond(SDL_cond * cond) |
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{ |
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if (cond) { |
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if (cond->wait_sem) { |
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SDL_DestroySemaphore(cond->wait_sem); |
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} |
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if (cond->wait_done) { |
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SDL_DestroySemaphore(cond->wait_done); |
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} |
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if (cond->lock) { |
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SDL_DestroyMutex(cond->lock); |
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} |
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SDL_free(cond); |
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} |
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} |
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/* Restart one of the threads that are waiting on the condition variable */ |
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int |
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SDL_CondSignal(SDL_cond * cond) |
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{ |
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if (!cond) { |
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7037
3fedf1f25b94
Make SDL_SetError and friends unconditionally return -1.
Ryan C. Gordon <icculus@icculus.org>
parents:
7009
diff
changeset
|
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return SDL_SetError("Passed a NULL condition variable"); |
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} |
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/* If there are waiting threads not already signalled, then |
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signal the condition and wait for the thread to respond. |
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*/ |
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SDL_LockMutex(cond->lock); |
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if (cond->waiting > cond->signals) { |
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++cond->signals; |
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SDL_SemPost(cond->wait_sem); |
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SDL_UnlockMutex(cond->lock); |
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SDL_SemWait(cond->wait_done); |
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} else { |
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SDL_UnlockMutex(cond->lock); |
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} |
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return 0; |
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} |
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/* Restart all threads that are waiting on the condition variable */ |
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int |
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SDL_CondBroadcast(SDL_cond * cond) |
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{ |
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if (!cond) { |
|
7037
3fedf1f25b94
Make SDL_SetError and friends unconditionally return -1.
Ryan C. Gordon <icculus@icculus.org>
parents:
7009
diff
changeset
|
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return SDL_SetError("Passed a NULL condition variable"); |
7009 | 110 |
} |
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/* If there are waiting threads not already signalled, then |
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signal the condition and wait for the thread to respond. |
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*/ |
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SDL_LockMutex(cond->lock); |
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if (cond->waiting > cond->signals) { |
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int i, num_waiting; |
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num_waiting = (cond->waiting - cond->signals); |
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cond->signals = cond->waiting; |
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for (i = 0; i < num_waiting; ++i) { |
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SDL_SemPost(cond->wait_sem); |
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} |
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/* Now all released threads are blocked here, waiting for us. |
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Collect them all (and win fabulous prizes!) :-) |
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*/ |
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SDL_UnlockMutex(cond->lock); |
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for (i = 0; i < num_waiting; ++i) { |
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SDL_SemWait(cond->wait_done); |
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} |
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} else { |
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SDL_UnlockMutex(cond->lock); |
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} |
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return 0; |
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} |
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/* Wait on the condition variable for at most 'ms' milliseconds. |
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The mutex must be locked before entering this function! |
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The mutex is unlocked during the wait, and locked again after the wait. |
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Typical use: |
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Thread A: |
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SDL_LockMutex(lock); |
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while ( ! condition ) { |
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SDL_CondWait(cond, lock); |
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} |
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SDL_UnlockMutex(lock); |
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Thread B: |
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SDL_LockMutex(lock); |
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... |
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condition = true; |
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... |
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SDL_CondSignal(cond); |
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SDL_UnlockMutex(lock); |
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*/ |
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int |
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SDL_CondWaitTimeout(SDL_cond * cond, SDL_mutex * mutex, Uint32 ms) |
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{ |
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int retval; |
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if (!cond) { |
|
7037
3fedf1f25b94
Make SDL_SetError and friends unconditionally return -1.
Ryan C. Gordon <icculus@icculus.org>
parents:
7009
diff
changeset
|
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return SDL_SetError("Passed a NULL condition variable"); |
7009 | 166 |
} |
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/* Obtain the protection mutex, and increment the number of waiters. |
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This allows the signal mechanism to only perform a signal if there |
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are waiting threads. |
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*/ |
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SDL_LockMutex(cond->lock); |
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++cond->waiting; |
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SDL_UnlockMutex(cond->lock); |
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/* Unlock the mutex, as is required by condition variable semantics */ |
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SDL_UnlockMutex(mutex); |
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/* Wait for a signal */ |
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if (ms == SDL_MUTEX_MAXWAIT) { |
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retval = SDL_SemWait(cond->wait_sem); |
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} else { |
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retval = SDL_SemWaitTimeout(cond->wait_sem, ms); |
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} |
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/* Let the signaler know we have completed the wait, otherwise |
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the signaler can race ahead and get the condition semaphore |
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if we are stopped between the mutex unlock and semaphore wait, |
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giving a deadlock. See the following URL for details: |
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http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html |
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*/ |
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SDL_LockMutex(cond->lock); |
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if (cond->signals > 0) { |
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/* If we timed out, we need to eat a condition signal */ |
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if (retval > 0) { |
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SDL_SemWait(cond->wait_sem); |
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} |
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/* We always notify the signal thread that we are done */ |
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SDL_SemPost(cond->wait_done); |
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/* Signal handshake complete */ |
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--cond->signals; |
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} |
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--cond->waiting; |
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SDL_UnlockMutex(cond->lock); |
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/* Lock the mutex, as is required by condition variable semantics */ |
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SDL_LockMutex(mutex); |
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return retval; |
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} |
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/* Wait on the condition variable forever */ |
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int |
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SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex) |
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{ |
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return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT); |
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} |
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/* vi: set ts=4 sw=4 expandtab: */ |