Using rb-inotify within Async task

[brandonhilkert]

We're looking to use https://github.com/guard/rb-inotify as a wrapped class that will monitor a path on the filesystem and also invoke other work. We're seeing the monitor get blocked on startup of the Reactor.

Here's a simplified example

Async::Reactor.run do |task|
  task.async do |subtask|
    SyslogMonitor.run
  end

  task.async do |subtask|
    while true
      periodic_work
      subtask.sleep 300
    end
  end
end

class SyslogMonitor
  def self.run
    Async do |task|
      File.open(LOG_PATH, "r") do |f|
        f.seek(0, IO::SEEK_END)

        queue = INotify::Notifier.new

        queue.watch(LOG_PATH, :modify) do
          change = f.read

          Async do |task|
            task.sleep 2
            process_change
          end
        end

        queue.run
      end
    end
  end
end

Would we have to use rb-inotify differently for it to be compatible with the reactor?

BTW - the whole family of async gems have been incredibly helpful. Thanks so much for your time and effort on them!

[ioquatix]

@brandonhilkert I'm happy to hear it's been super useful - if you have commercial use case please consider sponsoring a gem within the eco-system: https://github.com/socketry/community#funding

Does rb-inotify expose a file descriptor? If so, you need to put it into an Async::Wrapper and wait on it. Otherwise, it will block the task.

The other option is to use a thread to run the queue.watch and feed events back using a queue. However, that is more work and less efficient.

So, my first suggestion is to check how we can integrate it better.

[brandonhilkert]

I assume your comment here would be the idea, right?

[ioquatix]

Yes, that's basically it.

wrapper = Async::Wrapper.new(io)
wrapper.wait_readable

io.read

[ioquatix]

Feel free to give me an update. We should add documentation to clarify this use case.

[ioquatix]

In Async 2.x world, all IO is now non-blocking, so this should be a non-issue. Please try it out and open a new issue if you are still having problems.