Correctly stop link_manager sender and receiver threads

This changes the destroy_link_manager() function to:
* call a new function message_get_unlock() to unlock the sending thread from
  its blocking message_get()
* calls pthread_cancel() on the receiving thread, because this unlocks any
  blocking read from a file descriptor

The same message_get_unlock() function has been added ringbuffer_queue to keep
the interfaces the same (it does nothing, because ringbuffer_queue is
non-blocking).

openair2/UTIL/ASYNC_IF/message_queue.c

@@ -56,6 +56,10 @@ message_queue_t *new_message_queue(void)
   if (pthread_cond_init(ret->cond, NULL))
     goto error;
 
+  ret->head = NULL;
+  ret->tail = NULL;
+  ret->exit = 0;
+
   return ret;
 
 error:
@@ -121,10 +125,15 @@ int message_get(message_queue_t *queue, void **data, int *priority)
     goto error;
 
   while (queue->count == 0) {
-    if (pthread_cond_wait(queue->cond, queue->mutex)) {
+    int rc = pthread_cond_wait(queue->cond, queue->mutex);
+    if (rc != 0) {
       pthread_mutex_unlock(queue->mutex);
       goto error;
     }
+    if (queue->exit) {
+      pthread_mutex_unlock(queue->mutex);
+      return 0;
+    }
   }
 
   m = queue->head;
@@ -148,6 +157,14 @@ error:
   return -1;
 }
 
+void message_get_unlock(message_queue_t *queue)
+{
+  pthread_mutex_lock(queue->mutex);
+  queue->exit = 1;
+  pthread_mutex_unlock(queue->mutex);
+  pthread_cond_signal(queue->cond);
+}
+
 /* when calling this function, the queue must not be used anymore (we don't lock it) */
 /* we suppose that the data pointer in messages was allocated by malloc/calloc/realloc */
 void destroy_message_queue(message_queue_t *queue)