# 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
# Corresponds to the mailbox of an actor
class Mailbox[E]
	super BlockingQueue[E]

	# The associated actor
	var actor: Actor is noautoinit

	# init self with an associated actor
	init with_actor(actor: Actor) do
		self.actor = actor
		sys.active_actors.increment
	end

	# Adding the signal to release eventual waiting thread(s)
	redef fun push(e) do
		mutex.lock
		if real_collection.is_empty and not actor.working then
			actor.working = true
			sys.active_actors.increment
			real_collection.push(e)
			self.cond.signal
		else
			real_collection.push(e)
		end
		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
		if real_collection.is_empty then
			actor.working = false
			sys.active_actors.decrement
			while real_collection.is_empty do self.cond.wait(mutex)
		end
		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