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Created attachment 4305 [details]
this bug's comment

(This description also can be found in attachment file, which should be more easy to read due to the text format.)

I use the SDL_cond as below:

In some threads:
SDL_LockMutex(mtx);
SDL_CondWaitTimout(cond, mtx, 10);
SDL_UnlockMutex(mtx);

In another thread:
SDL_CondBroadcast(cond);

This will cause deadlock sometime.

I analyse the calling stream and find a issue:

Thread 1:                      					Thread 2:                      				Thread 3:
(SDL_CondWaitTimeout)          					(SDL_CondSignal	            				(SDL_CondWaitTimeout)
												/SDL_CondBroadcast)

....
SDL_LockMutex(cond->lock);
++cond->waiting;
SDL_UnlockMutex(cond->lock);
SDL_UnlokcMutex(mutex);

// Here timeout when waiting
retval=SDL_SemWaitTimeout(cond->wait_sem, ms);
												...
												SDL_LockMutex(cond->lock);
												if(cond->waiting > cond->signals) {
													++cond->signals;
													SDL_SemPost(cond->wait_sem);
													SDL_UnlockMutex(cond->lock);
													SDL_SemWait(cond->wait_done);
												}
												...
																						....
																						SDL_LockMutex(cond->lock);
																						++cond->waiting;
																						SDL_UnlockMutex(cond->lock);
																						SDL_UnlokcMutex(mutex);

																						// Here catch the semaphore signaled in thread 2
																						retval=SDL_SemWaitTimeout(cond->wait_sem, ms);										
SDL_LockMutex(cond->lock);
if (cond->signals > 0) {
	if (retval > 0) {
		// !!!Here deadlock occurs as the
		// semaphore catched by thread 3.
		SDL_SemWait(cond->wait_sem);
    }
    SDL_SemPost(cond->wait_done);

    --cond->signals;
}
--cond->waiting;
SDL_UnlockMutex(cond->lock);
SDL_LockMutex(mutex);																	SDL_LockMutex(cond->lock);
																						if (cond->signals > 0) {
																							if (retval > 0) {
																								// !!!Here deadlock occurs as the
																								// semaphore catched by thread 3.
																								SDL_SemWait(cond->wait_sem);
																							}
																							SDL_SemPost(cond->wait_done);

																							--cond->signals;
																						}
																						--cond->waiting;
																						SDL_UnlockMutex(cond->lock);
																						SDL_LockMutex(mutex);