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Date: Tue, 21 Feb 2017 20:15:26 +0000
From: Eric Wong <e@80x24.org>
To: Jeremy Evans <code@jeremyevans.net>
Cc: unicorn-public@bogomips.org
Subject: Re: Patch: Add after_worker_exit configuration option
Message-ID: <20170221201526.GA7035@starla>
References: <20170221191923.GH93742@jeremyevans.local>
 <20170221194320.GA26617@whir>
 <20170221200216.GJ93742@jeremyevans.local>
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Jeremy Evans <code@jeremyevans.net> wrote:
> On 02/21 07:43, Eric Wong wrote:
> > Jeremy Evans <code@jeremyevans.net> wrote:
> > > This option can be used to implement custom behavior for handling
> > > worker exits.  For example, let's say you have a specific request
> > > that crashes a worker process, which you expect to be due to a
> > > improperly programmed C extension. By modifying your worker to
> > > save request related data in a temporary file and using this option,
> > > you can get a record of what request is crashing the application,
> > > which will make debugging easier.
> > > 
> > > This is not a complete patch as it doesn't include tests, but
> > > before writing tests I wanted to see if this is something you'd
> > > consider including in unicorn.
> > 
> > What advantage does this have over Ruby's builtin at_exit?
> 
> at_exit is not called if the interpreter crashes:
> 
> ruby -e 'at_exit{File.write('a.txt', 'a')}; Process.kill :SEGV, $$' 2>/dev/null
> ([ -f a.txt ] && echo at_exit called) || echo at_exit not called

Ah, thanks.  I didn't read the code carefully, enough.
The commit message and documentation should reflect that it's
called in the master and not the worker.

Anyways, this is probably OK since I can't think of a less
intrusive or more generic (across all Rack servers) way of doing
it.  So I'm inclined to accept some version of this.

> --- a/lib/unicorn/http_server.rb
> +++ b/lib/unicorn/http_server.rb
> @@ -14,7 +14,8 @@ class Unicorn::HttpServer
>    attr_accessor :app, :timeout, :worker_processes,
>                  :before_fork, :after_fork, :before_exec,
>                  :listener_opts, :preload_app,
> -                :orig_app, :config, :ready_pipe, :user
> +                :orig_app, :config, :ready_pipe, :user,
> +                :after_worker_exit

I've been trying to reduce the method entry overhead across
the board.  Since this is a new field, can it be attr_writer
solely for configurator?

I don't think there's reader dependency other than below...

> @@ -395,8 +396,7 @@ def reap_all_workers
>          proc_name 'master'
>        else
>          worker = @workers.delete(wpid) and worker.close rescue nil
> -        m = "reaped #{status.inspect} worker=#{worker.nr rescue 'unknown'}"
> -        status.success? ? logger.info(m) : logger.error(m)
> +        after_worker_exit.call(self, worker, status)

Which can be made to access the ivar directly:

	   @after_worker_exit.call(self, worker, status)