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, #inspect, #print_hierarchy, #reap, #traverse

Constructor Details

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

#stoppedObject (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

.selectorObject


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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.


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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.


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

#closevoid

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 223

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.


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# File 'lib/async/reactor.rb', line 233

def closed?
  @selector.nil?
end

#finished?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

#loggerObject


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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?
  
  until @stopped
    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 @ready.empty?
      interval = @timers.wait_interval
    else
      # if there are tasks ready to execute, don't sleep:
      interval = 0
    end
    
    # If there is no interval to wait (thus no timers), and no tasks, we could be done:
    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&.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
  end
  
  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.


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# File 'lib/async/reactor.rb', line 239

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

#stopvoid

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


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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 272

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

#to_sObject


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

def to_s
  "\#<#{self.description} (#{@stopped ? 'stopped' : 'running'})>"
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.


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# File 'lib/async/reactor.rb', line 256

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