# A Blocking queue implemented from a `ConcurrentList`
# `shift` is blocking if there isn't any element in `self`
# `push` or `unshift` releases every blocking threads
class BlockingQueue[E]
	super ConcurrentList[E]

	# Used to block or signal on waiting threads
	private var cond = new PthreadCond

	# Adding the signal to release eventual waiting thread(s)
	redef fun push(e) do
		mutex.lock
		real_collection.push(e)
		self.cond.signal
		real_collection.push(e)
		mutex.unlock
	end

	redef fun unshift(e) do
		mutex.lock
		real_collection.unshift(e)
		self.cond.signal
		mutex.unlock
	end

	# If empty, blocks until an item is inserted with `push` or `unshift`
	redef fun shift do
		mutex.lock
		while real_collection.is_empty do self.cond.wait(mutex)
		var r = real_collection.shift
		mutex.unlock
		return r
	end

	redef fun is_empty do
		mutex.lock
		var r = real_collection.is_empty
		mutex.unlock
		return r
	end
end