class method

Ractor.select

(?) -> ::Array[untyped]

Ractor.select(*ractors_or_ports) → [ractor or port, obj]

# File tmp/rubies/ruby-4.0.0/ractor.rb, line 308
def self.select(*ports)
  raise ArgumentError, 'specify at least one Ractor::Port or Ractor' if ports.empty?

  monitors = {} # Ractor::Port => Ractor

  ports = ports.map do |arg|
    case arg
    when Ractor
      port = Ractor::Port.new
      monitors[port] = arg
      arg.monitor port
      port
    when Ractor::Port
      arg
    else
      raise ArgumentError, "should be Ractor::Port or Ractor"
    end
  end

  begin
    result_port, obj = __builtin_ractor_select_internal(ports)

    if r = monitors[result_port]
      [r, r.value]
    else
      [result_port, obj]
    end
  ensure
    # close all ports for join
    monitors.each do |port, r|
      r.unmonitor port
      port.close
    end
  end
end

Blocks the current Thread until one of the given ports has received a message. Returns an array of two elements where the first element is the Port and the second is the received object. This method can also accept Ractor objects themselves, and in that case will wait until one has terminated and return a two-element array where the first element is the ractor and the second is its termination value.

Example

p1, p2 = Ractor::Port.new, Ractor::Port.new
ps = [p1, p2]
rs = 2.times.map do |i|
  Ractor.new(ps.shift, i) do |p, i|
    sleep rand(0.99)
    p.send("r#{i}")
    sleep rand(0.99)
    "r#{i} done"
  end
end

waiting_on = [p1, p2, *rs]
until waiting_on.empty?
  received_on, obj = Ractor.select(*waiting_on)
  waiting_on.delete(received_on)
  puts obj
end

# r0
# r1
# r1 done
# r0 done

The following example is almost equivalent to ractors.map(&:value) except the thread is unblocked when any of the ractors has terminated as opposed to waiting for their termination in the array element order.

Example

values = []
until ractors.empty?
  r, val = Ractor.select(*ractors)
  ractors.delete(r)
  values << val
end

Ruby version changes

4.0
- Ractor.select now only accepts Ractors and Ports. If Ractors are given, it returns when a Ractor terminates.

See also .recv .shareable? .receive .shareable_lambda also in 4.1 · 3.4 · 3.3 · 3.2 · 3.1 · 3.0

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