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Date: Mon, 28 Nov 2016 17:57:35 +0000
From: Eric Wong <e@80x24.org>
To: Peter Giacomo Lombardo <peter.lombardo@instana.com>
Cc: unicorn-public@bogomips.org
Subject: Re: Storing Multiple Blocks for Configurator Hooks
Message-ID: <20161128175735.GA25338@starla>
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Peter Giacomo Lombardo <peter.lombardo@instana.com> wrote:
> Please excuse if this has been discussed or already decided upon - searches came up with nothing.

Nope, I don't recall this coming up on the list.

> Has unicorn considered allowing multiple blocks to be supplied for Configurator Hooks (e.g. after_fork et. al.)?

Yes, but only briefly in the earliest stages of the project.  I
rejected it since it make things more difficult to debug and
track down.

Nowadays, it could break an existing use case:

	after_fork do
	  # ... many lines
	end
	after_fork {} # nothing, temporarily disable initial block

	(I realize putting " if false" after "end" can also disable
	 the block, but I suspect many folks who configure unicorn
	 are not regularly Rubyists).

> Currently, it seems that only one block can be specified:
> https://bogomips.org/unicorn.git/tree/lib/unicorn/configurator.rb#n628
> 
> If instead this were stored as an array of blocks, gems could register their own blocks to be run when the hooks are called which would result in less end-user burden and easier on-ramping to get a running system.  

It seems like it would be a management problem if the config got
too big and were split into many pieces.  It would be extra bad
if it were difficult to know ordering (FIFO? LIFO?) and which
part of the config each part is in.

You can manage an array yourself:

	af_cb = []
	after_fork { af_cb.each(&:call) }
	af_cb << lambda { ... }
	af_cb << lambda { ... }

> (Confronting the ActiveRecord establish_connection and Redis re-connect seem to be a rite of passage into using Unicorn)

preload_app has always defaulted to "false" for this reason :)

Also, isn't a mere disconnect all that's necessary nowadays, as
connections are made on demand?  At least that's how Sequel
behaves.  I haven't touched AR/Rails in years (since a JS
engine became mandatory).