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Re: Concern about memory management with SRFs

From: Joe Conway <mail(at)joeconway(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Concern about memory management with SRFs
Date: 2002-08-29 01:19:54
Message-ID: 3D6D76BA.80600@joeconway.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Tom Lane wrote:
> I think we should document that any memory that is allocated in the
> first call for use in subsequent calls must come from the memory context
> saved in FuncCallContext (and let's choose a more meaningful name than
> fmctx, please).  This would mean adding code like
> 
> 	oldcontext = MemoryContextSwitchTo(funcctx->fmctx);
> 
> 	...
> 
> 	MemoryContextSwitchTo(oldcontext);
> 
> around the setup code that follows SRF_FIRSTCALL_INIT.  Then it would be
> safe for nodeFunctionscan.c to do a reset before each function call.

That sounds like a good plan.

But can/should we wrap those calls in either existing or new macros? Or 
is it better to have the function author keenly aware of the memory 
management details? I tend to think the former is better.

Maybe SRF_FIRSTCALL_INIT()(init_MultiFuncCall()) should:
- save CurrentMemoryContext to funcctx->per_call_memory_ctx
   (new member of the struct)
- save fcinfo->flinfo->fn_mcxt to funcctx->multi_call_memory_ctx
   (nee funcctx->fmctx)
- leave fcinfo->flinfo->fn_mcxt as the current memory context when it
   exits

Then SRF_PERCALL_SETUP() (per_MultiFuncCall()) can change back to 
funcctx->per_call_memory_ctx.

Would this work?

Joe


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