class Async::List

A general doublely linked list. This is used internally by {Async::Barrier} and {Async::Condition} to manage child tasks.

def added(node)

A callback that is invoked when an item is added to the list. 
def added(node)
	@size += 1
	return node
end

def append(node)

Append a node to the end of the list. 
def append(node)
	if node.head
		raise ArgumentError, "Node is already in a list!"
	end
	
	node.tail = self
	@head.tail = node
	node.head = @head
	@head = node
	
	return added(node)
end

def each(&block)

@returns [List] Returns self.
@yields {|node| ...} Yields each node in the list.

Iterate over each node in the linked list. It is generally safe to remove the current node, any previous node or any future node during iteration. 
def each(&block)
	return to_enum unless block_given?
	
	Iterator.each(self, &block)
	
	return self
end

def empty?

@returns [Boolean] Returns true if the list is empty. 
def empty?
	@size == 0
end

def first

@returns [Node] Returns the first node in the list, if it is not empty. 
def first
	# validate!
	
	current = @tail
	
	while !current.equal?(self)
		if current.is_a?(Iterator)
			current = current.tail
		else
			return current
		end
	end
	
	return nil
end

def include?(needle)

@returns [Boolean] Returns true if the node is in the list.
@parameter needle [Node] The node to search for.

Determine whether the given node is included in the list. 
def include?(needle)
	self.each do |item|
		return true if needle.equal?(item)
	end
	
	return false
end

def initialize

Initialize a new, empty, list. 
def initialize
	@head = self
	@tail = self
	@size = 0
end

def last

@returns [Node] Returns the last node in the list, if it is not empty. 
def last
	# validate!
	
	current = @head
	
	while !current.equal?(self)
		if current.is_a?(Iterator)
			current = current.head
		else
			return current
		end
	end
	
	return nil
end

def prepend(node) 

def prepend(node)
	if node.head
		raise ArgumentError, "Node is already in a list!"
	end
	
	node.head = self
	@tail.head = node
	node.tail = @tail
	@tail = node
	
	return added(node)
end

def remove(node)

@returns [Node] Returns the node if it was removed, otherwise nil.
@raises [ArgumentError] If the node is not part of this list.

You should be careful to only remove nodes that are part of this list.

Remove the node. If it was already removed, this will raise an error. 
def remove(node)
	# One downside of this interface is we don't actually check if the node is part of the list defined by `self`. This means that there is a potential for a node to be removed from a different list using this method, which in can throw off book-keeping when lists track size, etc.
	unless node.head
		raise ArgumentError, "Node is not in a list!"
	end
	
	remove!(node)
end

def remove!(node) 

def remove!(node)
ad.tail = node.tail
il.head = node.head
marks the node as being removed, and causes remove to fail if called a 2nd time.
ad = nil
tail = nil
removed(node)

def remove?(node)

@returns [Node] Returns the node if it was removed, otherwise nil.

You should be careful to only remove nodes that are part of this list.

Remove the node if it is in a list. 
def remove?(node)
	if node.head
		return remove!(node)
	end
	
	return nil
end

def removed(node)

A callback that is invoked when an item is removed from the list. 
def removed(node)
	@size -= 1
	return node
end

def shift 

def shift
	if node = first
		remove!(node)
	end
end

def stack(node, &block)

@returns [Object] Returns the result of the block.
@yields {|node| ...} Yields the node.
Add the node, yield, and the remove the node. 
def stack(node, &block)
	append(node)
	return yield(node)
ensure
	remove!(node)
end

def to_a

Fast, safe, unbounded accumulation of children. 
def to_a
	items = []
	current = self
	
	while current.tail != self
		unless current.tail.is_a?(Iterator)
			items << current.tail
		end
		
		current = current.tail
	end
	
	return items
end

def to_s

Print a short summary of the list. 
def to_s
	sprintf("#<%s:0x%x size=%d>", self.class.name, object_id, @size)
end