r6:Function:queue guaranteed enqueue
int queue_guaranteed_enqueue( struct queue_state *qs, void *user_data );
struct queue_state *qs
- A queue state as allocated by queue_new.
- A void pointer of user data which will be queued into the queue.
Returns 1 on a successful enqueue. Returns 0 if enqueing failed. Enqueuing only fails if malloc fails.
The function queue_enqueue fails only when the queue's freelist is empty. In this event, queue_guaranteed_push can be called, which allocates a new element and enqueues using that new element, thus guaranteeing an enqueue, barring the event of malloc failure.