On Tue, Dec 19, 2017 at 12:24 AM, Regina Obe <l...@pcorp.us> wrote: > On December 13th this change to context creation was committed, which broke > PostGIS trunk compile against PostgreSQL 11 head. > https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=9fa6f00b1308d > d10da4eca2f31ccbfc7b35bb461 > > Ticketed in PostGIS here: > https://trac.osgeo.org/postgis/ticket/3946 > > > It's been broken for a couple of months > https://trac.osgeo.org/postgis/ticket/3904 with just core dumping but at > least it used to compile before December 13th. > > > In going thru the changes I see that MemoryContextCreate was changed to not > return a context anymore and to take in pointer to the context that should > be returned among other changes. > > I also notice that MemoryContextCreate seems to be rarely used in PostgreSQL > code in places I would expect and instead AllocSetContextCreateExtended is > used. > > So is the preferred approach to not use MemoryContextCreate in extensions > and instead for PG < 11 use AllocSetContextCreate and PG >= use > AllocSetContextCreateExtended? > > Sorry if my questions don't make any sense. Still trying to grapple with > all these memory context functions and how each is different from the other. > > For reference, one of the slices of code we have in place that broke looks > something like this and we've got I think at least 5 more such instances > sprinkled in PostGIS code base. > > https://git.osgeo.org/gitea/postgis/postgis/src/branch/svn-trunk/libpgcommon > /lwgeom_transform.c#L550 > > > > MemoryContext PJMemoryContext; > POSTGIS_DEBUGF(3, "adding SRID %d with proj4text \"%s\" to query > cache at index %d", srid, proj_str, PROJ4Cache->PROJ4SRSCacheCount); > > PJMemoryContext = MemoryContextCreate(T_AllocSetContext, 8192, > &PROJ4SRSCacheContextMethods, > > PROJ4Cache->PROJ4SRSCacheContext, > "PostGIS PROJ4 PJ Memory > Context");
As Regina noted, we're working in https://trac.osgeo.org/postgis/ticket/3946 Our use of MemoryContextCreate is solely in order to get use MemoryContextDelete as a callback so that, at the end of a statement, we can clean up externally allocated memory that we're holding in a cache. If we had some other callback to use for "the statement is complete, you can clean up now", we could avoid all this mucking around with raw MemoryContexts entirely. The MemoryContext trick/hack is very old, perhaps a callback or hook has been added since then that we could make use of?
