Re: Safe memory allocation functions

Andres Freund wrote:
> On 2015-01-16 12:56:18 -0300, Alvaro Herrera wrote:

> > So how about something like
> > 
> > #define ALLOCFLAG_HUGE            0x01
> > #define ALLOCFLAG_NO_ERROR_ON_OOM    0x02
> > void *
> > MemoryContextAllocFlags(MemoryContext context, Size size, int flags);

> I don't know, this seems a bit awkward to use.  Your earlier example with
> the *Huge variant that returns a smaller allocation doesn't really
> convince me - that'd need a separate API anyway.

What example was that?  My thinking was that the mcxt.c function would
return NULL if the request was not satisfied; only the caller would be
entitled to retry with a smaller size.  I was thinking in something like

baseflag = ALLOCFLAG_NO_ERROR_ON_OOM;
reqsz = SomeHugeValue;
while (true)
{ptr = MemoryContextAllocFlags(cxt, reqsz,        ALLOCFLAG_HUGE | baseflag);if (ptr != NULL)    break;    /* success
*/
/* too large, retry with a smaller allocation */reqsz *= 0.75;
/* if under some limit, have it fail next time */if (reqsz < SomeHugeValue * 0.1)    baseflag = 0;
}
/* by here, you know ptr points to a memory area of size reqsz, which is  between SomeHugeValue * 0.1 and
SomeHugeValue.*/
 


Were you thinking of something else?

> I definitely do not want to push the nofail stuff via the
> MemoryContextData-> API into aset.c. Imo aset.c should always return
> NULL and then mcxt.c should throw the error if in the normal palloc()
> function.

Sure, that seems reasonable ...

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services