[postgis-tickets] [PostGIS] #3946: PostgreSQL 11 head no longer compiles against PostGIS trunk

[PostGIS]

#3946: PostgreSQL 11 head no longer compiles against PostGIS trunk
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  Reporter:  robe     |      Owner:  robe
      Type:  defect   |     Status:  new
  Priority:  blocker  |  Milestone:  PostGIS 2.5.0
 Component:  postgis  |    Version:  trunk
Resolution:           |   Keywords:
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Comment (by pramsey):

 I only see `MemoryContextCreate` in three places, but in at least two of
 them (geos prepared and proj) they are being used in ways that are not
 consistent with `AllocSetContextCreate`. They are being used as memory
 management tricks by the caching code for geos prepared geometry and proj
 handles. The problem is that geos and proj both allocate outside the pgsql
 memory manager, and we want to free up any resources in the cache once a
 pgsql statement ends. But we have no way of knowing when a statement is
 complete. So we create our own memory context and tuck it into the
 statement context. Now, when the statement ends, it has to first tell our
 own context to clean itself up. And into the cleanup routine of our
 context we add the code that frees up our cached geos/proj objects.

 Basically, we don't use those contexts for storing things, we just use
 them to hide a callback. So we cannot change those over to
 `AllocSetContextCreate` calls, we have to figure out how to continue to
 use them, or figure some other way to get a callback when a statement
 ends.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3946#comment:4>
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