class Async::Barrier

@public Since ‘stable-v1`.
A synchronization primitive, which allows one task to wait for a number of other tasks to complete. It can be used in conjunction with {Semaphore}.

def async(*arguments, parent: (@parent or Task.current), **options, &block)

@asynchronous Executes the given block concurrently.
Execute a child task and add it to the barrier. 
def async(*arguments, parent: (@parent or Task.current), **options, &block)
	task = parent.async(*arguments, **options, &block)
	
	@tasks << task
	
	return task
end

def empty?

@returns [Boolean]
Whether there are any tasks being held by the barrier. 
def empty?
	@tasks.empty?
end

def initialize(parent: nil)

@public Since `stable-v1`.
@parameter parent [Task | Semaphore | Nil] The parent for holding any children tasks.
Initialize the barrier. 
def initialize(parent: nil)
	@tasks = []
	
	@parent = parent
end

def size

The number of tasks currently held by the barrier. 
def size
	@tasks.size
end

def stop

@asynchronous May wait for tasks to finish executing.
Stop all tasks held by the barrier. 
def stop
	# We have to be careful to avoid enumerating tasks while adding/removing to it:
	tasks = @tasks.dup
	tasks.each(&:stop)
end

def wait

@asynchronous Will wait for tasks to finish executing.
Wait for all tasks. 
def wait
	# TODO: This would be better with linked list.
	while @tasks.any?
		task = @tasks.first
		
		begin
			task.wait
		ensure
			# We don't know for sure that the exception was due to the task completion.
			unless task.running?
				# Remove the task from the waiting list if it's finished:
				@tasks.shift if @tasks.first == task
			end
		end
	end
end