# The promise of a value which will be set asynchronously
class Future[E]
	# Value promised by `self`
	var value: nullable E = null

	# Mutex for synchronisation
	protected var mutex = new Mutex

	# Condition variable for synchronisation
	protected var cond: nullable PthreadCond = null

	# Can be used to check if the value is available without waiting
	protected var is_done = false

	# Set the value and signal so that, someone waiting for `value` can retrieve it
	fun set_value(value: E) do
		mutex.lock
		is_done = true
		self.value = value
		var cond = self.cond
		if cond != null then cond.signal
		mutex.unlock
	end

	# Return immediatly if `value` is set, or block waiting for `value` to be set
	fun join: E do
		mutex.lock
		if not is_done then
			var cond = self.cond
			if cond == null then
				cond = new PthreadCond
				self.cond = cond
			end
			cond.wait(mutex)
		end
		mutex.unlock
		return value
	end
end