Forking

[zhulik]

Hello,

what would be general recommendations for forking from the event loop? Unfortunately I couldn't find anything in the docs.

I naively tried forking from within a Sync block:

Sync do
  Process.fork do
  end
end

but it raises an error when a forked process finishes:

/home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/task.rb:168:in `stop': Stopping current task! (Async::Stop)
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/node.rb:339:in `block in stop_children'
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/node.rb:88:in `each'
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/node.rb:338:in `stop_children'
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/node.rb:333:in `stop'
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/node.rb:320:in `terminate'
        from /home/user/.asdf/installs/ruby/3.1.2/lib/ruby/gems/3.1.0/gems/async-2.0.2/lib/async/scheduler.rb:53:in `close'
        from /home/user/script.rb:2:in `fork'

Thanks!

[ioquatix]

Generally speaking, forking is very hard to do correctly in the scope of a scheduler, so I would advise to use Process.spawn. Do you mind explaining why you want to fork?

[zhulik]

I wanted to use a gem called parallel(uses fork) to run some cpu-bound operations in parallel from an async task

[ioquatix]

In Ruby 3.x & Async 2.x, using a thread gets you a non-blocking context outside of the reactor:

Async do
  thread = Thread.new do
    # Not running in scheduler
    # parallel work / fork okay here.
  end
  thread.join # non-blocking
end

[zhulik]

It works! Thanks a lot!