Horton

shmem_startup_hook called twice on Windows

Sami Imseih <samimseih@gmail.com>

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From: Sami Imseih <samimseih@gmail.com>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-15T14:17:22Z
Lists: pgsql-hackers 
Hi,

While working on a related area, I noticed that shmem_startup_hook
is called twice under EXEC_BACKEND.

The first call occurs in CreateSharedMemoryAndSemaphores() during
postmaster startup (!IsUnderPostmaster), which is expected.

The second call happens in AttachSharedMemoryStructs() (when
EXEC_BACKEND is defined), and this occurs in normal backends
(IsUnderPostmaster).

The second call does not seem correct. The startup hook that should
only run during
postmaster initialization, AFAIK.

Blame shows that this change was introduced in commit 69d903367c,
but I could not determine the rationale from the discussion,
so it may have been an oversight.

Thoughts?

--
Sami Imseih
Amazon Web Services (AWS)

Commits

  1. Fix documentation for shmem_startup_hook.

  2. test_slru: Fix LWLock tranche allocation in EXEC_BACKEND builds.

  3. doc: Reorganize section for shared memory and LWLocks.

  4. Refactor CreateSharedMemoryAndSemaphores