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, #head, #parent, #tail

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Node

#annotate, #backtrace, #children?, #consume, #description, #print_hierarchy, #stop, #terminate, #transient?, #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 74

def initialize(parent = nil, selector: self.class.selector, logger: nil)
	super(parent)
	
	@selector = selector
	@timers = Timers::Group.new
	@logger = logger
	
	@ready = []
	@running = []
	
	if Scheduler.supported?
		@scheduler = Scheduler.new(self)
	else
		@scheduler = nil
	end
	
	@interrupted = false
	@guard = Mutex.new
	@blocked = 0
	@unblocked = []
end

Instance Attribute Details

#loggerObject (readonly)

Returns the value of attribute logger


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

def logger
  @logger
end

#schedulerObject (readonly)

Returns the value of attribute scheduler


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# File 'lib/async/reactor.rb', line 96

def scheduler
  @scheduler
end

Class Method Details

.run(*arguments, **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 48

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

.selectorObject


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# File 'lib/async/reactor.rb', line 62

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 188

def << fiber
	@ready << fiber
end

#async(*arguments, **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 153

def async(*arguments, **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 the method call where possible.
	# - Execute determinstically where possible.
	# - Avoid scheduler overhead if no blocking operation is performed.
	task.run(*arguments)
	
	# Console.logger.debug "Initial execution of task #{fiber} complete (#{result} -> #{fiber.alive?})..."
	return task
end

#block(blocker, timeout) ⇒ Object


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# File 'lib/async/reactor.rb', line 100

def block(blocker, timeout)
	fiber = Fiber.current
	
	if timeout
		timer = @timers.after(timeout) do
			if fiber.alive?
				fiber.resume(false)
			end
		end
	end
	
	begin
		@blocked += 1
		Task.yield
	ensure
		@blocked -= 1
	end
ensure
	timer&.cancel
end

#closeObject

Stop each of the children tasks and close the selector.


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# File 'lib/async/reactor.rb', line 297

def close
	# This is a critical step. Because tasks could be stored as instance variables, and since the reactor is (probably) going out of scope, we need to ensure they are stopped. Otherwise, the tasks will belong to a reactor that will never run again and are not stopped:
	self.terminate
	
	@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 307

def closed?
	@selector.nil?
end

#fiber(&block) ⇒ Object


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# File 'lib/async/reactor.rb', line 129

def fiber(&block)
	if @scheduler
		Fiber.new(blocking: false, &block)
	else
		Fiber.new(&block)
	end
end

#finished?Boolean

Returns:

  • (Boolean)

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# File 'lib/async/reactor.rb', line 199

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

#interruptObject

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


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# File 'lib/async/reactor.rb', line 177

def interrupt
	@guard.synchronize do
		unless @interrupted
			@interrupted = true
			@selector.wakeup
		end
	end
end

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


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# File 'lib/async/reactor.rb', line 169

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

#run(*arguments, **options, &block) ⇒ Object

Run the reactor until all tasks are finished. Proxies arguments to #async immediately before entering the loop, if a block is provided.


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# File 'lib/async/reactor.rb', line 279

def run(*arguments, **options, &block)
	raise RuntimeError, 'Reactor has been closed' if @selector.nil?
	
	@scheduler&.set!
	
	initial_task = self.async(*arguments, **options, &block) if block_given?
	
	while self.run_once
		# Round and round we go!
	end
	
	return initial_task
ensure
	@scheduler&.clear!
	Console.logger.debug(self) {"Exiting run-loop because #{$! ? $! : 'finished'}."}
end

#run_once(timeout = nil) ⇒ Boolean

Run one iteration of the event loop.

Parameters:

  • timeout (Float | nil) (defaults to: nil)

    the maximum timeout, or if nil, indefinite.

Returns:

  • (Boolean)

    whether there is more work to do.


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# File 'lib/async/reactor.rb', line 207

def run_once(timeout = nil)
	# Console.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
	end
	
	if @unblocked.any?
		unblocked = Array.new
		
		@guard.synchronize do
			unblocked, @unblocked = @unblocked, unblocked
		end
		
		while fiber = unblocked.pop
			fiber.resume if fiber.alive?
		end
	end
	
	if @ready.empty?
		interval = @timers.wait_interval
	else
		# if there are tasks ready to execute, don't sleep:
		interval = 0
	end
	
	# If we are finished, we stop the task tree and exit:
	if self.finished?
		return false
	end
	
	# If there is no interval to wait (thus no timers), and no tasks, we could be done:
	if interval.nil?
		# Allow the user to specify a maximum interval if we would otherwise be sleeping indefinitely:
		interval = timeout
	elsif interval < 0
		# We have timers ready to fire, don't sleep in the selctor:
		interval = 0
	elsif timeout and interval > timeout
		interval = timeout
	end
	
	# Console.logger.info(self) {"Selecting with #{@children&.size} children with interval = #{interval ? interval.round(2) : 'infinite'}..."}
	if monitors = @selector.select(interval)
		monitors.each do |monitor|
			monitor.value.resume
		end
	end
	
	@timers.fire
	
	# We check and clear the interrupted flag here:
	if @interrupted
		@guard.synchronize do
			@interrupted = false
		end
		
		return false
	end
	
	# The reactor still has work to do:
	return true
end

#sleep(duration) ⇒ Object

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


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# File 'lib/async/reactor.rb', line 313

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

#stopped?Boolean

Returns:

  • (Boolean)

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# File 'lib/async/reactor.rb', line 141

def stopped?
	@children.nil?
end

#to_sObject


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

def to_s
	"\#<#{self.description} #{@children&.size || 0} children (#{stopped? ? 'stopped' : 'running'})>"
end

#unblock(blocker, fiber) ⇒ Object


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# File 'lib/async/reactor.rb', line 122

def unblock(blocker, fiber)
	@guard.synchronize do
		@unblocked << fiber
		@selector.wakeup
	end
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 330

def with_timeout(timeout, exception = TimeoutError)
	fiber = Fiber.current
	
	timer = @timers.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 193

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