[postgis-users] Memory management in postgres (with liblwgeom functions in particular)

[Igor Stassiy]

Hello,

I am developing a C++ extension (most of the code is C++) for postgres that
links dynamically with liblwgeom, without linking to postgis. I call
liblwgeom functions that serialize/deserialize LWGEOM* (and similar
structures) that don't need a backend like GEOS.

I wonder how is the memory freed when we call lwerror, as the transaction
will be terminated (elog/ereport create a long jump), so if I call
liblwgeoms functions from within C++, the stack will not be unwind and even
if I use smart pointers it wouldn't make a difference (right?).

On the contrary, when Postgis module loads itself, in _PG_init it overrides
memory allocation functions of liblwgeom with pg_alloc and pg_free. Which
in turn call palloc and pfree. And in this case when we call lwerror, the
memory that we allocated is freed automatically (right?).

I guess (just a guess) it has something to do with the memory context and
when a memory context is "closed" the entire memory allocated within would
be freed. But lwalloc by default is malloc, so does Postgres do something
extremely clever like overriding malloc with its palloc?

Thank you,
Igor
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