[fix #129] Fix register/de-register bug when process is restarted out-of-band.

[apinstein]

Fixes a bug when a process is restarted out-of-band wherby the
original pid was never unwatched and thus would trigger
false-positives by god on noticing process exits.

I am not 100% sure that this doesn't cause problems elsewhere. Not exactly sure how to test and don't know enough about the overall architecture to know what I don't know about how all this works across different process mechanisms.

In any case I'm going to use this on my prod box for a bit and see how it goes.

Would love to have additional feedback.

[eric]

Nice! I agree the current logic isn't right.

I think we could change the definition of pid() to something like this:

      def pid
        @pid ||= self.pid_file ? File.read(self.pid_file).strip.to_i : self.watch.pid
      end

and leave the rest of the logic as-is and it would do what we intended.

[apinstein]

Yeah I suppose that could work as well. I was just trying to keep the concern separate since I didn't know what else was going on.

Thanks for reviewing!

On Aug 6, 2013, at 5:15 PM, Eric Lindvall notifications@github.com wrote:

Nice! I agree the current logic isn't right.

I think we could change the definition of pid() to something like this:

  def pid
    @pid ||= self.pid_file ? File.read(self.pid_file).strip.to_i : self.watch.pid
  end

and leave the rest of the logic as-is and it would do what we intended.

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[apinstein]

@eric your idea only half worked; the pid needed to be cleared out on de-register so that it would re-bootstrap itself based on the watch/pid file. Otherwise it would continue monitoring the prior pid.

What do you think?

[chetan]

I've been running into this issue for a while (and #127 as well) but came up with a slightly different fix which you can see here:

https://github.com/chetan/god/compare/dangling_process_exit

In addition, I changed my config to disable the clean_pid_file behavior and changed the process_exit condition to transition to :init instead of :start, so that it has a chance to pickup the new pid instead of just blindly trying to start and throw errors.

edit: I'm not 100% sure that the Monitor synchronization is necessary, but it does seem there are possible race conditions there otherwise.