Clear stale 'post's on the event semphaphore

OpenAL32/event.c

@@ -13,6 +13,11 @@ static int EventThread(void *arg)
 {
     ALCcontext *context = arg;
 
+    /* Clear all pending posts on the semaphore. */
+    while(alsem_trywait(&context->EventSem) == althrd_success)
+    {
+    }
+
     while(1)
     {
         AsyncEvent evt;

common/threads.c

@@ -354,6 +354,14 @@ int alsem_wait(alsem_t *sem)
     return althrd_error;
 }
 
+int alsem_trywait(alsem_t *sem)
+{
+    DWORD ret = WaitForSingleObject(*sem, 0);
+    if(ret == WAIT_OBJECT_0) return althrd_success;
+    if(ret == WAIT_TIMEOUT) return althrd_busy;
+    return althrd_error;
+}
+
 
 /* An associative map of uint:void* pairs. The key is the TLS index (given by
  * TlsAlloc), and the value is the altss_dtor_t callback. When a thread exits,
@@ -664,6 +672,14 @@ int alsem_wait(alsem_t *sem)
     return althrd_error;
 }
 
+int alsem_trywait(alsem_t *sem)
+{
+    if(sem_trywait(sem) == 0) return althrd_success;
+    if(errno == EWOULDBLOCK) return althrd_busy;
+    if(errno == EINTR) return -2;
+    return althrd_error;
+}
+
 
 int altss_create(altss_t *tss_id, altss_dtor_t callback)
 {

common/threads.h

@@ -237,6 +237,7 @@ int alsem_init(alsem_t *sem, unsigned int initial);
 void alsem_destroy(alsem_t *sem);
 int alsem_post(alsem_t *sem);
 int alsem_wait(alsem_t *sem);
+int alsem_trywait(alsem_t *sem);
 
 int altss_create(altss_t *tss_id, altss_dtor_t callback);
 void altss_delete(altss_t tss_id);