class Async::Node

def add_child child
 ||= Children.new
.insert(child)
_parent(self)

def annotate(annotation)
	if block_given?
		previous_annotation = @annotation
		@annotation = annotation
		yield
		@annotation = previous_annotation
	else
		@annotation = annotation
	end
end

def backtrace(*arguments)
	nil
end

def children?
	@children != nil && !@children.empty?
end

def consume
	if parent = @parent and finished?
		parent.delete_child(self)
		
		if @children
			@children.each do |child|
				if child.finished?
					delete_child(child)
				else
					# In theory we don't need to do this... because we are throwing away the list. However, if you don't correctly update the list when moving the child to the parent, it foobars the enumeration, and subsequent nodes will be skipped, or in the worst case you might start enumerating the parents nodes.
					delete_child(child)
					parent.add_child(child)
				end
			end
			
			@children = nil
		end
		
		parent.consume
	end
end

def delete_child(child)
.delete(child)
_parent(nil)

def description
	@object_name ||= "#{self.class}:#{format '%#018x', object_id}#{@transient ? ' transient' : nil}"
	
	if @annotation
		"#{@object_name} #{@annotation}"
	elsif line = self.backtrace(0, 1)&.first
		"#{@object_name} #{line}"
	else
		@object_name
	end
end

def finished?
	@children.nil? || @children.finished?
end

def initialize(parent = nil, annotation: nil, transient: false)
	@parent = nil
	@children = nil
	
	@annotation = annotation
	@object_name = nil
	
	@transient = transient
	
	@head = nil
	@tail = nil
	
	if parent
		parent.add_child(self)
	end
end

def parent=(parent)
	return if @parent.equal?(parent)
	
	if @parent
		@parent.delete_child(self)
		@parent = nil
	end
	
	if parent
		parent.add_child(self)
	end
	
	return self
end

def print_backtrace(out, indent, node)
	if backtrace = node.backtrace
		backtrace.each_with_index do |line, index|
			out.puts "#{indent}#{index.zero? ? "→ " : "  "}#{line}"
		end
	end
end

def print_hierarchy(out = $stdout, backtrace: true)
	self.traverse do |node, level|
		indent = "\t" * level
		
		out.puts "#{indent}#{node}"
		
		print_backtrace(out, indent, node) if backtrace
	end
end

def root
	@parent&.root || self
end

def set_parent parent
 parent

def stop(later = false)
	# The implementation of this method may defer calling `stop_children`.
	stop_children(later)
end

def stop_children(later = false)
en&.each do |child|
stop(later) unless child.transient?

def stopped?
	@children.nil?
end

def terminate
	# Attempt to stop the current task immediately, and all children:
	stop(false)
	
	# If that doesn't work, take more serious action:
	@children&.each do |child|
		child.terminate
	end
end

def to_s
	"\#<#{self.description}>"
end

def transient?
	@transient
end

def traverse(level = 0, &block)
	yield self, level
	
	@children&.each do |child|
		child.traverse(level + 1, &block)
	end
end