Class: Async::Idler

Inherits:
Object
  • Object
show all
Defined in:
lib/async/idler.rb

Overview

A load balancing mechanism that can be used process work when the system is idle.

Instance Method Summary collapse

Constructor Details

#initialize(maximum_load = 0.8, backoff: 0.001, parent: nil) ⇒ Idler

Create a new idler.



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# File 'lib/async/idler.rb', line 16

def initialize(maximum_load = 0.8, backoff: 0.001, parent: nil)
	@maximum_load = maximum_load
	@backoff = backoff
	@current = backoff
	
	@parent = parent
	@mutex = Mutex.new
end

Instance Method Details

#async(*arguments, parent: (@parent or Task.current), **options, &block) ⇒ Object

Wait until the system is idle, then execute the given block in a new task.



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# File 'lib/async/idler.rb', line 33

def async(*arguments, parent: (@parent or Task.current), **options, &block)
	wait
	
	# It is crucial that we optimistically execute the child task, so that we prevent a tight loop invoking this method from consuming all available resources.
	parent.async(*arguments, **options, &block)
end

#wait ⇒ Object

Wait until the system is idle, according to the maximum load specified.

If the scheduler is overloaded, this method will sleep for an exponentially increasing amount of time.



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# File 'lib/async/idler.rb', line 43

def wait
	@mutex.synchronize do
		scheduler = Fiber.scheduler
		
		while true
			load = scheduler.load
			
			if load <= @maximum_load
				# Even though load is okay, if @current is high, we were recently overloaded. Sleep proportionally to prevent burst after load drop:
				if @current > @backoff
					# Sleep a fraction of @current to rate limit:
					sleep(@current - @backoff)
					
					# Decay @current gently towards @backoff:
					alpha = 0.99
					@current *= alpha + (1.0 - alpha) * (load / @maximum_load)
				end
				
				break
			else
				# We're overloaded, so increase backoff:
				@current *= (load / @maximum_load)
				sleep(@current)
			end
		end
	end
end