Feature #20805: Allow Ractor#send from a signal trap Proc

• Status: Open
• Assignee: -
• Target version: -

[kirs (Kir Shatrov)]

It was surfaced in https://bugs.ruby-lang.org/issues/18139 that Ractor is designed to "unexpected interruption free" and it's not supposed to have a kill-like method.

A better alternative to that would be allow the main Ractor to consume a shutdown signal from the pipe.

Example:

shutdown_ractor = Ractor.new do
  Ractor.recv # Wait for a signal
end

# Signal trap for SIGTERM
Signal.trap("TERM") do
  puts "Received SIGTERM, shutting down..."
  shutdown_ractor.send(:shutdown) # Send the shutdown signal
end

pipe = Ractor.new do
  loop do
    r, value = Ractor.select(Ractor.recv, shutdown_ractor)

    if r == shutdown_ractor # Shutdown signal received
      break
    else
      Ractor.yield(value, move: true) # Normal operation
    end
  end
end

However, it's not possible to do Ractor#send from a trap Proc right now:

<internal:ractor>:282:in `new': can not isolate a Proc because it accesses outer variables (shutdown_ractor). (ArgumentError)

From what I've gathered, it makes it impossible to implement any graceful shutdown in a process with a few Ractors running.

[alanwu (Alan Wu)]

It works if you make shutdown_ractor a constant:

p Process.pid

SHUTDOWN_RACTOR = Ractor.new do
  Ractor.recv # Wait for a signal
  puts "goodbye"
  exit!
end

# Signal trap for SIGTERM
Signal.trap("TERM") do
  puts "Received SIGTERM, shutting down..."
  SHUTDOWN_RACTOR.send(:shutdown) # Send the shutdown signal
end

sleep

ruby -v test.rb
ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [arm64-darwin24]
79270
test.rb:3: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
Received SIGTERM, shutting down...
goodbye

Not to minimize the usability issue you experienced.