Method try_dequeue

include/dmlc/blockingconcurrentqueue.h:696–705

	// Never allocates. Thread-safe.
	template<typename U>
	inline bool try_dequeue(U& item)
	{
		if (sema->tryWait()) {
			while (!inner.try_dequeue(item)) {
				continue;
			}
			return true;
		}
		return false;
	}

	// Attempts to dequeue from the queue using an explicit consumer token.
	// Returns false if all producer streams appeared empty at the time they