Class: RactorPool

Inherits:
Object
  • Object
show all
Defined in:
lib/ractor-pool.rb,
lib/ractor-pool/version.rb,
sig/generated/ractor-pool.rbs,
sig/generated/ractor-pool/version.rbs

Overview

A thread-safe, lock-free pool of Ractor workers with coordinator or round-robin dispatch for distributing work.

RactorPool manages a fixed number of worker ractors that process work items in parallel. The :coordinator strategy (the default) routes each work item to whichever worker is currently idle via a dedicated coordinator Ractor, so a slow item on one worker does not block faster items from being picked up by other workers. Use it when work items have variable cost. The :round_robin strategy dispatches work to workers in turn, so a slow item on one worker queues the next item destined for that worker behind it, even if other workers are idle. Use it when work items have uniform cost. Results are collected and passed to a result handler running in a separate thread.

Examples:

Basic usage

results = []
worker = -> (work) { work * 2 }
pool = RactorPool.new(size: 4, worker: worker) { |result| results << result }

10.times { |index| pool << index }
pool.shutdown

p results #=> [2, 0, 6, 4, 14, 10, 8, 16, 18, 12]

Without result handler

counter = Atom.new(0)
worker = proc do |work|
  counter.swap { |current_value| current_value + 1 }
  work * 2
end
pool = RactorPool.new(size: 4, worker: worker)

10.times { |index| pool << index }
pool.shutdown

p counter.value #=> 10

See Also:

Defined Under Namespace

Classes: EnqueuedWorkAfterShutdownError, Error

Constant Summary collapse

STRATEGIES =

Returns:

  • (Object) 
%i[coordinator round_robin].freeze
SHUTDOWN =

Returns:

  • (::Symbol) 
:shutdown
VERSION =

Returns:

  • (::String) 
"0.4.0"

Instance Method Summary collapse

Constructor Details

#initialize(size: Etc.nprocessors, worker:, strategy: :coordinator, name: nil, on_error: nil) {|result| ... } ⇒ RactorPool

Creates a new RactorPool with the specified number of workers.

Examples:

With result handler

pool = RactorPool.new(size: 4, worker: proc { it }) { |result| puts result }

Without result handler

pool = RactorPool.new(size: 4, worker: proc { it })

With round-robin strategy

pool = RactorPool.new(size: 4, strategy: :round_robin, worker: proc { it })

With error handler

error_count = Atom.new(0)
on_error = proc { error_count.swap { |count| count + 1 } }
pool = RactorPool.new(size: 4, worker: proc { raise }, on_error: on_error)

Parameters:

  • size (Integer) (defaults to: Etc.nprocessors) —

    number of worker ractors to create

  • worker (Proc) —

    a shareable proc that processes each work item

  • strategy (Symbol) (defaults to: :coordinator) —

    dispatch strategy, either :coordinator (the default) or :round_robin

  • name (String, nil) (defaults to: nil) —

    optional name for the pool, used in thread/ractor names

  • on_error (Proc, nil) (defaults to: nil) —

    optional shareable proc called with the raised exception when a worker raises

  • worker: (^(untyped) -> untyped)
  • size: (Integer) (defaults to: Etc.nprocessors)
  • strategy: (Symbol) (defaults to: :coordinator)
  • name: (String, nil) (defaults to: nil)
  • on_error: (^(Exception) -> void, nil) (defaults to: nil)

Yield Parameters:

  • result (Object) —

    the result returned by the worker proc

Raises:

  • (ArgumentError) —

    if size is not a positive integer

  • (ArgumentError) —

    if worker is not a proc

  • (ArgumentError) —

    if strategy is not :coordinator or :round_robin

  • (ArgumentError) —

    if on_error is given but is not a proc



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# File 'lib/ractor-pool.rb', line 107

def initialize(size: Etc.nprocessors, worker:, strategy: :coordinator, name: nil, on_error: nil, &result_handler)
  raise ArgumentError, "size must be a positive Integer" unless size.is_a?(Integer) && size > 0
  raise ArgumentError, "worker must be a Proc" unless worker.is_a?(Proc)
  raise ArgumentError, "strategy must be one of #{STRATEGIES.inspect}" unless STRATEGIES.include?(strategy)
  raise ArgumentError, "on_error must be a Proc" if on_error && !on_error.is_a?(Proc)

  @size = size
  @worker = Ractor.shareable_proc(&worker)
  @strategy = strategy
  @name = name
  @on_error = Ractor.shareable_proc(&on_error) if on_error
  @result_handler = result_handler

  @in_flight = Atom.new(0)
  @shutdown  = Atom.new(false)
  @next_worker_index = Atom.new(-1) if size > 1 && strategy == :round_robin

  @result_port = Ractor::Port.new if result_handler
  @error_port  = Ractor::Port.new unless on_error
  @coordinator = start_coordinator if size > 1 && strategy == :coordinator
  @workers = start_workers
  @collector = start_collector
  @error_collector = start_error_collector
end

Instance Method Details

#<<(work) ⇒ void

This method returns an undefined value.

Queues a work item to be processed by an available worker.

Examples:

pool << "http://example.com/page1"
pool << "http://example.com/page2"

Parameters:

  • work (Object) —

    the work item to process

Raises:



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# File 'lib/ractor-pool.rb', line 143

def <<(work)
  raise EnqueuedWorkAfterShutdownError if @shutdown.value

  @in_flight.swap { |count| count + 1 }

  if @shutdown.value
    @in_flight.swap { |count| count - 1 }
    raise EnqueuedWorkAfterShutdownError
  end

  target = if @coordinator
             @coordinator
           elsif @next_worker_index
             @workers[@next_worker_index.swap { |index| (index + 1) % @size }]
           else
             @workers.first
           end

  begin
    target.send(work, move: true)
  ensure
    @in_flight.swap { |count| count - 1 }
  end
end

#shutdown ⇒ void

This method returns an undefined value.

Shuts down the pool gracefully.

This method:

  1. Prevents new work from being queued
  2. Waits for all in-flight work submissions to complete
  3. Allows all queued work to complete
  4. Waits for all workers to finish
  5. Waits for all results and errors to be processed

This method is idempotent and can be called multiple times safely.

Examples:

pool.shutdown


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# File 'lib/ractor-pool.rb', line 185

def shutdown
  already_shutdown = false
  @shutdown.swap do |current|
    if current
      already_shutdown = true
      current
    else
      true
    end
  end
  return if already_shutdown

  Thread.pass until @in_flight.value.zero?

  if @coordinator
    @coordinator.send(SHUTDOWN, move: true)
    @workers.each(&:join)
    @coordinator.join
  else
    @workers.each { |worker| worker.send(SHUTDOWN, move: true) }
    @workers.each(&:join)
    @result_port&.send(SHUTDOWN, move: true)
  end
  @error_port&.send(SHUTDOWN, move: true)
  @error_collector&.join
  @collector&.join
end

#start_collector ⇒ Thread?

Returns:

  • (Thread, nil) 


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# File 'lib/ractor-pool.rb', line 295

def start_collector
  return unless @result_handler

  thread_name = String.new("#{self.class.name} collector thread")
  thread_name << " for #{@name}" if @name

  Thread.new(@result_port, @result_handler, thread_name) do |result_port, result_handler, name|
    Thread.current.name = name

    loop do
      result = result_port.receive
      break if result == SHUTDOWN

      result_handler.call(result)
    end
  end
end

#start_coordinator ⇒ Ractor

Returns:

  • (Ractor) 


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# File 'lib/ractor-pool.rb', line 216

def start_coordinator
  ractor_name = String.new("#{self.class.name} coordinator ractor")
  ractor_name << " for #{@name}" if @name

  Ractor.new(@size, @result_port, name: ractor_name) do |worker_count, result_port|
    work_queue = []
    waiting_workers = []
    shutdown_received = false
    workers_finished = 0

    loop do
      case data = Ractor.receive
      when SHUTDOWN
        shutdown_received = true

        workers_finished += waiting_workers.size
        waiting_workers.each { |worker| worker.send(SHUTDOWN, move: true) }
        waiting_workers.clear
        if workers_finished == worker_count
          result_port&.send(SHUTDOWN, move: true)
          break
        end

      when Ractor
        ractor = data

        if work_queue.any?
          ractor.send(work_queue.shift, move: true)
        elsif shutdown_received
          ractor.send(SHUTDOWN, move: true)

          workers_finished += 1
          if workers_finished == worker_count
            result_port&.send(SHUTDOWN, move: true)
            break
          end
        else
          waiting_workers << ractor
        end

      else
        work = data

        if waiting_workers.any?
          waiting_workers.shift.send(work, move: true)
        else
          work_queue << work
        end
      end
    end
  end
end

#start_error_collector ⇒ Thread?

Returns:

  • (Thread, nil) 


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# File 'lib/ractor-pool.rb', line 314

def start_error_collector
  return if @on_error

  thread_name = String.new("#{self.class.name} error collector thread")
  thread_name << " for #{@name}" if @name

  Thread.new(@error_port, thread_name) do |error_port, name|
    Thread.current.name = name

    loop do
      message = error_port.receive
      break if message == SHUTDOWN

      warn message
    end
  end
end

#start_workers ⇒ Array[Ractor]

Returns:

  • (Array[Ractor]) 


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# File 'lib/ractor-pool.rb', line 270

def start_workers
  @size.times.map do |index|
    ractor_name = String.new("#{self.class.name} ractor #{index}")
    ractor_name << " for #{@name}" if @name

    Ractor.new(@worker, @on_error, @error_port, @coordinator, @result_port, name: ractor_name) do |worker, on_error, error_port, coordinator, result_port|
      loop do
        coordinator&.send(Ractor.current, move: true)

        work = Ractor.receive
        break if work == SHUTDOWN

        begin
          result = worker.call(work)

          result_port&.send(result, move: true)
        rescue => error
          on_error ? on_error.call(error) : error_port.send(error.full_message, move: true)
        end
      end
    end
  end
end