Fixed bug #570

SDL_SemWaitTimeout in src/thread/generic/SDL_syssem.c line 179 (SVN trunk):

--sem->count;

should be

if (retval == 0) {
    --sem->count;
}

Without this, sem->count will underflow on timeout effectively breaking the
semaphore. It appears that the implementation has been wrong since the initial
revision.

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%403843

src/thread/generic/SDL_syssem.c

@@ -165,7 +165,9 @@ int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
 		                             sem->count_lock, timeout);
 	}
 	--sem->waiters_count;
-	--sem->count;
+	if (retval == 0) {
+		--sem->count;
+	}
 	SDL_UnlockMutex(sem->count_lock);
 
 	return retval;