[ruby-core:119620] [Ruby master Feature#20805] Allow Ractor#send from a signal trap Proc

25 Oct 2024

      Issue #20805 has been updated by alanwu (Alan Wu).

It works if you make `shutdown_ractor` a constant:

```ruby
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
```

```shell
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.

----------------------------------------
Feature #20805: Allow Ractor#send from a signal trap Proc
https://bugs.ruby-lang.org/issues/20805#change-110242

* Author: kirs (Kir Shatrov)
* Status: Open
----------------------------------------
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:

```ruby
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.

-- 
https://bugs.ruby-lang.org/