Class: Async::Reactor

Inherits:
Node
  • Object
show all
Extended by:
Forwardable
Defined in:
lib/async/reactor.rb

Overview

An asynchronous, cooperatively scheduled event reactor.

Instance Attribute Summary collapse

Attributes inherited from Node

#annotation, #children, #parent

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Node

#annotate, #consume, #description, #print_hierarchy, #reap, #traverse

Constructor Details

#initialize(parent = nil, selector: self.class.selector, logger: nil) ⇒ Reactor

Returns a new instance of Reactor.



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# File 'lib/async/reactor.rb', line 73

def initialize(parent = nil, selector: self.class.selector, logger: nil)
	super(parent)
	
	@selector = selector
	@timers = Timers::Group.new
	@logger = logger
	
	@ready = []
	@running = []
	
	@stopped = true
end

Instance Attribute Details

#stopped ⇒ Object (readonly) 



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# File 'lib/async/reactor.rb', line 95

def stopped
  @stopped
end

Class Method Details

.run(*args, **options, &block) ⇒ Object

The preferred method to invoke asynchronous behavior at the top level.

  • When invoked within an existing reactor task, it will run the given block asynchronously. Will return the task once it has been scheduled.
  • When invoked at the top level, will create and run a reactor, and invoke the block as an asynchronous task. Will block until the reactor finishes running.


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# File 'lib/async/reactor.rb', line 45

def self.run(*args, **options, &block)
	if current = Task.current?
		reactor = current.reactor
		
		return reactor.async(*args, **options, &block)
	else
		reactor = self.new(**options)
		
		begin
			return reactor.run(*args, &block)
		ensure
			reactor.close
		end
	end
end

.selector ⇒ Object 



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# File 'lib/async/reactor.rb', line 61

def self.selector
	if backend = ENV['ASYNC_BACKEND']&.to_sym
		if NIO::Selector.backends.include?(backend)
			return NIO::Selector.new(backend)
		else
			warn "Could not find ASYNC_BACKEND=#{backend}!"
		end
	end
	
	return NIO::Selector.new
end

Instance Method Details

#<<(fiber) ⇒ Object

Schedule a fiber (or equivalent object) to be resumed on the next loop through the reactor.

Parameters:

  • fiber (#resume) —

    The object to be resumed on the next iteration of the run-loop.



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# File 'lib/async/reactor.rb', line 146

def << fiber
	@ready << fiber
end

#async(*args, **options) {|Task| ... } ⇒ Task

Start an asynchronous task within the specified reactor. The task will be executed until the first blocking call, at which point it will yield and and this method will return.

This is the main entry point for scheduling asynchronus tasks.

Yields:

  • (Task) —

    Executed within the task.

Returns:

  • (Task) —

    The task that was scheduled into the reactor.



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# File 'lib/async/reactor.rb', line 112

def async(*args, **options, &block)
	task = Task.new(self, **options, &block)
	
	# I want to take a moment to explain the logic of this.
	# When calling an async block, we deterministically execute it until the
	# first blocking operation. We don't *have* to do this - we could schedule
	# it for later execution, but it's useful to:
	# - Fail at the point of call where possible.
	# - Execute determinstically where possible.
	# - Avoid overhead if no blocking operation is performed.
	task.run(*args)
	
	# logger.debug "Initial execution of task #{fiber} complete (#{result} -> #{fiber.alive?})..."
	return task
end

#close ⇒ void

This method returns an undefined value.

Stop each of the children tasks and close the selector.



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# File 'lib/async/reactor.rb', line 222

def close
	@children&.each(&:stop)
	
	# TODO Should we also clear all timers?
	@selector.close
	@selector = nil
end

#closed? ⇒ Boolean

Check if the selector has been closed.

Returns:

  • (Boolean) 


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# File 'lib/async/reactor.rb', line 232

def closed?
	@selector.nil?
end

#finished? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/reactor.rb', line 157

def finished?
	# I'm not sure if checking `@running.empty?` is really required.
	super && @ready.empty? && @running.empty?
end

#logger ⇒ Object 



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# File 'lib/async/reactor.rb', line 86

def logger
	@logger ||= Console.logger
end

#register(io, interest, value = Fiber.current) ⇒ Object 



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# File 'lib/async/reactor.rb', line 128

def register(io, interest, value = Fiber.current)
	monitor = @selector.register(io, interest)
	monitor.value = value
	
	return monitor
end

#run(*args, &block) ⇒ Object

Run the reactor until either all tasks complete or #stop is invoked. Proxies arguments to #async immediately before entering the loop.



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# File 'lib/async/reactor.rb', line 164

def run(*args, &block)
	raise RuntimeError, 'Reactor has been closed' if @selector.nil?
	
	@stopped = false
	
	initial_task = self.async(*args, &block) if block_given?
	
	@timers.wait do |interval|
		# logger.debug(self) {"@ready = #{@ready} @running = #{@running}"}
		
		if @ready.any?
			# running used to correctly answer on `finished?`, and to reuse Array object.
			@running, @ready = @ready, @running
			
			@running.each do |fiber|
				fiber.resume if fiber.alive?
			end
			
			@running.clear
			
			# if there are tasks ready to execute, don't sleep.
			if @ready.any?
				interval = 0
			else
				# The above tasks may schedule, cancel or affect timers in some way. We need to compute a new wait interval for the blocking selector call below:
				interval = @timers.wait_interval
			end
		end
		
		# As timeouts may have been updated, and caused fibers to complete, we should check this.
		if interval.nil?
			if self.finished?
				# If there is nothing to do, then finish:
				return initial_task
			end
		elsif interval < 0
			# We have timers ready to fire, don't sleep in the selctor:
			interval = 0
		end
		
		# logger.debug(self) {"Selecting with #{@children&.count} children with interval = #{interval.inspect}..."}
		if monitors = @selector.select(interval)
			monitors.each do |monitor|
				monitor.value.resume
			end
		end
	end until @stopped
	
	return initial_task
ensure
	logger.debug(self) {"Exiting run-loop because #{$! ? $! : 'finished'}."}
	
	@stopped = true
end

#sleep(duration) ⇒ Object

Put the calling fiber to sleep for a given ammount of time.

Parameters:

  • duration (Numeric) —

    The time in seconds, to sleep for.



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# File 'lib/async/reactor.rb', line 238

def sleep(duration)
	fiber = Fiber.current
	
	timer = self.after(duration) do
		if fiber.alive?
			fiber.resume
		end
	end
	
	Task.yield
ensure
	timer.cancel if timer
end

#stop ⇒ void

This method returns an undefined value.

Stop the reactor at the earliest convenience. Can be called from a different thread safely.



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# File 'lib/async/reactor.rb', line 137

def stop
	unless @stopped
		@stopped = true
		@selector.wakeup
	end
end

#stopped? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/reactor.rb', line 97

def stopped?
	@stopped
end

#timeout(*args, &block) ⇒ Object

TODO remove



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# File 'lib/async/reactor.rb', line 271

def timeout(*args, &block)
	warn "#{self.class}\#timeout(...) is deprecated, use #{self.class}\#with_timeout(...) instead."
	
	with_timeout(*args, &block)
end

#to_s ⇒ Object 



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# File 'lib/async/reactor.rb', line 90

def to_s
	"<#{self.description} stopped=#{@stopped}>"
end

#with_timeout(timeout, exception = TimeoutError) ⇒ Object

Invoke the block, but after the specified timeout, raise TimeoutError in any currenly blocking operation. If the block runs to completion before the timeout occurs or there are no non-blocking operations after the timeout expires, the code will complete without any exception.

Parameters:

  • duration (Numeric) —

    The time in seconds, in which the task should complete.



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# File 'lib/async/reactor.rb', line 255

def with_timeout(timeout, exception = TimeoutError)
	fiber = Fiber.current
	
	timer = self.after(timeout) do
		if fiber.alive?
			error = exception.new("execution expired")
			fiber.resume error
		end
	end
	
	yield timer
ensure
	timer.cancel if timer
end

#yield(fiber = Fiber.current) ⇒ Object

Yield the current fiber and resume it on the next iteration of the event loop.



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# File 'lib/async/reactor.rb', line 151

def yield(fiber = Fiber.current)
	@ready << fiber
	
	Fiber.yield
end