class Async::Scheduler

def block(blocker, timeout)

@asynchronous May only be called on same thread as fiber scheduler.
Invoked when a fiber tries to perform a blocking operation which cannot continue. A corresponding call {unblock} must be performed to allow this fiber to continue. 
def block(blocker, timeout)
	# $stderr.puts "block(#{blocker}, #{Fiber.current}, #{timeout})"
	fiber = Fiber.current
	
	if timeout
		timer = @timers.after(timeout) do
			if fiber.alive?
				fiber.transfer(false)
			end
		end
	end
	
	begin
		@blocked += 1
		@selector.transfer
	ensure
		@blocked -= 1
	end
ensure
	timer&.cancel!
end