class Async::Barrier

@asynchronous Will wait for tasks to finish executing.

@returns [Integer | Nil] The number of tasks which were waited for, or `nil` if there were no tasks to wait for.
@yields {|task| ...} If a block is given, the unwaited task is yielded. You must invoke {Task#wait} yourself. In addition, you may `break` if you have captured enough results.

Wait for all tasks to complete by invoking {Task#wait} on each waiting task, which may raise an error. As long as the task has completed, it will be removed from the barrier.

def wait
	return nil if @tasks.empty?
	count = 0
	
	while true
		# Wait for a task to finish (we get the task node):
		break unless waiting = @finished.wait
		count += 1
		
		# Remove the task as it is now finishing:
		@tasks.remove?(waiting)
		
		# Get the task:
		task = waiting.task
		
		# If a block is given, the user can implement their own behaviour:
		if block_given?
			yield task
		else
			# Wait for it to either complete or raise an error:
			task.wait
		end
		
		break if @tasks.empty?
	end
	
	return count
end