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: NIO::Selector.new) ⇒ Reactor

Returns a new instance of Reactor.



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

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

Instance Attribute Details

#stopped ⇒ Object (readonly) 



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# File 'lib/async/reactor.rb', line 78

def stopped
  @stopped
end

Class Method Details

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

Instance Method Details

#<<(fiber) ⇒ Object

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



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# File 'lib/async/reactor.rb', line 127

def << fiber
  @ready << fiber
end

#async(*args) {|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 asynchronous task.

Returns:

  • (Task) —

    The task that was



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# File 'lib/async/reactor.rb', line 94

def async(*args, &block)
  task = Task.new(self, &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)
  
  # Async.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 203

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 214

def closed?
  @selector.nil?
end

#finished? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/reactor.rb', line 138

def finished?
  super && @ready.empty? && @running.empty?
end

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



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# File 'lib/async/reactor.rb', line 110

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 144

def run(*args, &block)
  raise RuntimeError, 'Reactor has been closed' if @selector.nil?
  
  @stopped = false
  
  # Allow the user to kick of the initial async tasks.
  initial_task = async(*args, &block) if block_given?
  
  @timers.wait do |interval|
    # running used to correctly answer on `finished?`, and to reuse Array object.
    @running, @ready = @ready, @running
    if @running.any?
      @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
    
    # - nil: no timers
    # - -ve: timers expired already
    # -   0: timers ready to fire
    # - +ve: timers waiting to fire
    if interval && interval < 0
      interval = 0
    end
    
    # Async.logger.debug(self) {"Updating #{@children.count} children..."}
    # As timeouts may have been updated, and caused fibers to complete, we should check this.
    
    # If there is nothing to do, then finish:
    if !interval && self.finished?
      return initial_task
    end
    
    # Async.logger.debug(self) {"Selecting with #{@children.count} fibers interval = #{interval.inspect}..."}
    if monitors = @selector.select(interval)
      monitors.each do |monitor|
        monitor.value.resume
      end
    end
  end until @stopped
  
  return initial_task
ensure
  Async.logger.debug(self) {"Exiting run-loop because #{$! ? $!.inspect : '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 220

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 119

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

#stopped? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/async/reactor.rb', line 80

def stopped?
  @stopped
end

#timeout(duration) ⇒ Object

Invoke the block, but after the timeout, raise TimeoutError in any currenly blocking operation.

Parameters:

  • duration (Integer) —

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



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

def timeout(duration)
  backtrace = caller
  fiber = Fiber.current
  
  timer = self.after(duration) do
    if fiber.alive?
      error = TimeoutError.new("execution expired")
      error.set_backtrace backtrace
      fiber.resume error
    end
  end
  
  yield
ensure
  timer.cancel if timer
end

#to_s ⇒ Object 



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

def to_s
  "<#{self.description} stopped=#{@stopped}>"
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 132

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