class IO::Event::PriorityHeap

def pop

Returns nil if the heap is empty. (and doesn't change the heap in that case)
Returns the earliest timer if the heap is non-empty and removes it from the heap. 
def pop
	# If the heap is empty:
	if @contents.empty?
		return nil
	end
	
	# If we have only one item, no swapping is required:
	if @contents.size == 1
		return @contents.pop
	end
	
	# Take the root of the tree:
	value = @contents[0]
	
	# Remove the last item in the tree:
	last = @contents.pop
	
	# Overwrite the root of the tree with the item:
	@contents[0] = last
	
	# Bubble it down into place:
	bubble_down(0)
	
	# validate!
	
	return value
end