Date: Thu, 12 Mar 2020 07:12:06 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org, Fabien COELHO <coelho@cri.ensmp.fr>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	David Steele <david@pgmasters.net>,
	"Bossart, Nathan" <bossartn@amazon.com>,
	Thomas Munro <thomas.munro@gmail.com>
Subject: Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at
 end-of-transaction
Message-ID: <20200312121206.GC29065@telsasoft.com>
References: <20200308173103.GC1357@telsasoft.com>
 <27334.1583692669@sss.pgh.pa.us>
 <20200308191456.GD1357@telsasoft.com>
 <5679.1583696409@sss.pgh.pa.us>
 <8034.1583699444@sss.pgh.pa.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <8034.1583699444@sss.pgh.pa.us>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk

On Sun, Mar 08, 2020 at 04:30:44PM -0400, Tom Lane wrote:
> BTW, another thing I noticed while looking around is that some of
> the functions using SRF_RETURN_DONE() think they should clean up
> memory beforehand.  This is a waste of code/cycles, as long as the
> memory was properly allocated in funcctx->multi_call_memory_ctx,
> because funcapi.c takes care of deleting that context.
> 
> We should probably document that *any* manual cleanup before
> SRF_RETURN_DONE() is an antipattern.  If you have to have cleanup,
> it needs to be done via RegisterExprContextCallback instead.

This part appears to be already in place since
e4186762ffaa4188e16702e8f4f299ea70988b96:

|The memory context that is current when the SRF is called is a transient
|context that will be cleared between calls. This means that you do not need to
|call pfree on everything you allocated using palloc; it will go away anyway.
|However, if you want to allocate any data structures to live across calls, you
|need to put them somewhere else. The memory context referenced by
|multi_call_memory_ctx is a suitable location for any data that needs to survive
|until the SRF is finished running. In most cases, this means that you should
|switch into multi_call_memory_ctx while doing the first-call setup.

-- 
Justin