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help / color / mirror / Atom feedFrom: Nathan Bossart <nathan@postgresql.org>
Subject: [PATCH v3 4/6] Convert PROC_HDR->startupBufferPinWaitBuf to an atomic variable.
Date: Tue, 8 Sep 2026 12:40:06 -0500
Currently, this variable is a Buffer that is accessed via a volatile
pointer. By converting it to an atomic variable, we can remove the
volatile qualifiers. No barriers are needed; as the comment there
notes, the value is published before the backends that read it are
signaled.
---
src/backend/storage/lmgr/proc.c | 12 +++---------
src/include/storage/proc.h | 2 +-
2 files changed, 4 insertions(+), 10 deletions(-)
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index ab65a6dbcc9..91fe2766640 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -238,7 +238,7 @@ ProcGlobalShmemInit(void *arg)
dlist_init(&ProcGlobal->autovacFreeProcs);
dlist_init(&ProcGlobal->bgworkerFreeProcs);
dlist_init(&ProcGlobal->walsenderFreeProcs);
- ProcGlobal->startupBufferPinWaitBuf = InvalidBuffer;
+ pg_atomic_init_u32(&ProcGlobal->startupBufferPinWaitBuf, InvalidBuffer);
pg_atomic_init_u32(&ProcGlobal->avLauncherProc, INVALID_PROC_NUMBER);
pg_atomic_init_u32(&ProcGlobal->walwriterProc, INVALID_PROC_NUMBER);
pg_atomic_init_u32(&ProcGlobal->checkpointerProc, INVALID_PROC_NUMBER);
@@ -767,10 +767,7 @@ InitAuxiliaryProcess(void)
void
SetStartupBufferPinWaitBuf(Buffer buffer)
{
- /* use volatile pointer to prevent code rearrangement */
- volatile PROC_HDR *procglobal = ProcGlobal;
-
- procglobal->startupBufferPinWaitBuf = buffer;
+ pg_atomic_write_u32(&ProcGlobal->startupBufferPinWaitBuf, buffer);
}
/*
@@ -779,10 +776,7 @@ SetStartupBufferPinWaitBuf(Buffer buffer)
Buffer
GetStartupBufferPinWaitBuf(void)
{
- /* use volatile pointer to prevent code rearrangement */
- volatile PROC_HDR *procglobal = ProcGlobal;
-
- return procglobal->startupBufferPinWaitBuf;
+ return pg_atomic_read_u32(&ProcGlobal->startupBufferPinWaitBuf);
}
/*
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 4c3f431b4eb..abe40001d9a 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -500,7 +500,7 @@ typedef struct PROC_HDR
/* Current shared estimate of appropriate spins_per_delay value */
int spins_per_delay;
/* Buffer that Startup process waits for pin on, or InvalidBuffer */
- Buffer startupBufferPinWaitBuf;
+ pg_atomic_uint32 startupBufferPinWaitBuf;
} PROC_HDR;
extern PGDLLIMPORT PROC_HDR *ProcGlobal;
--
2.55.0
--hwKv7DgSDwjNaYBK
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
filename=v3-0005-Convert-Sharedsort-s-worker-counters-to-atomic-va.patch
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To: pgsql-hackers@postgresql.org
Cc: nathan@postgresql.org
Subject: Re: [PATCH v3 4/6] Convert PROC_HDR->startupBufferPinWaitBuf to an atomic variable.
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