help in allocating shared module within a module
Hi all,
hope this is the right place to ask for, otherwise please point me in
the right resource.
I'm trying to develop a module that needs shared memory between
background workers.
The _PG_init calls a function to reserve the shared memory, which in
turn calls RequestAddinShmemSpace, which seems to fail. In fact, I
never got the debug line after the call to RequestAddinShmemSpaec and
_PG_init does not conitnue.
Here is my code skeleton:
void
_PG_init(void)
{
if ( ! process_shared_preload_libraries_in_progress )
return;
// set up the GUCs
_define_gucs();
// set up the shared memory
_create_shared_memory();
...
}
void
_create_shared_memory()
{
Size estimated_size = 10136:
elog( DEBUG2, "shared allocation %lu", estimated_size );
RequestAddinShmemSpace( estimated_size );
elog(DEBUG2, "never reached!" );
...
}
What am I missing here?
Thanks,
Luca
On Mon, 23 Dec 2024, 18:32 Luca Ferrari, <fluca1978@gmail.com> wrote:
Hi all,
hope this is the right place to ask for, otherwise please point me in
the right resource.
I'm trying to develop a module that needs shared memory between
background workers.The _PG_init calls a function to reserve the shared memory, which in
turn calls RequestAddinShmemSpace, which seems to fail. In fact, I
never got the debug line after the call to RequestAddinShmemSpaec and
_PG_init does not conitnue.Here is my code skeleton:
void
_PG_init(void)
{
[...]
// set up the shared memory
_create_shared_memory();
[...]
void
_create_shared_memory()
{
Size estimated_size = 10136:
[...]
RequestAddinShmemSpace( estimated_size );
[...]
What am I missing here?
Starting with PG15, shared memory should be allocated through a hook,
shmem_request_hook, and not through direct calls to
RequestAddinShmemSpace in _PG_init().
For specific info, see [0]https://www.postgresql.org/docs/current/xfunc-c.html#XFUNC-SHARED-ADDIN and [1]https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=4f2400cb3f10aa79f99fba680c198237da28dd38 which introduced
shmem_request_hook. PGPedia also has some info on how to deal with
older PG versions: [2]https://pgpedia.info/s/shmem_request_hook.html
I hope this helps.
Kind regards,
Matthias van de Meent
Neon (https://neon.tech)
[0]: https://www.postgresql.org/docs/current/xfunc-c.html#XFUNC-SHARED-ADDIN
[1]: https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=4f2400cb3f10aa79f99fba680c198237da28dd38
[2]: https://pgpedia.info/s/shmem_request_hook.html