From f451b44f81e57759a876fc9ca8360826da0537d9 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Thu, 26 Mar 2026 13:26:56 +0200 Subject: [PATCH v1 3/5] Use a separate spinlock to protect LWLockTranches Previously we reused the shmem allocator's ShmemLock for this. For the sake of modularity, it's more clear to have a dedicated lock. Now that lwlock.c has its own shared memory struct, this is easy to do. --- src/backend/storage/ipc/shmem.c | 8 +++----- src/backend/storage/lmgr/lwlock.c | 24 +++++++++++++----------- src/include/storage/shmem.h | 1 - 3 files changed, 16 insertions(+), 17 deletions(-) diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c index 0fb3bc59929..f392faa534f 100644 --- a/src/backend/storage/ipc/shmem.c +++ b/src/backend/storage/ipc/shmem.c @@ -105,7 +105,6 @@ static void *ShmemBase; /* start address of shared memory */ static void *ShmemEnd; /* end+1 address of shared memory */ static ShmemAllocatorData *ShmemAllocator; -slock_t *ShmemLock; /* points to ShmemAllocator->shmem_lock */ static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */ /* To get reliable results for NUMA inquiry we need to "touch pages" once */ @@ -166,7 +165,6 @@ InitShmemAllocator(PGShmemHeader *seghdr) ShmemAllocator->free_offset = offset; } - ShmemLock = &ShmemAllocator->shmem_lock; ShmemSegHdr = seghdr; ShmemBase = seghdr; ShmemEnd = (char *) ShmemBase + seghdr->totalsize; @@ -200,7 +198,7 @@ InitShmemAllocator(PGShmemHeader *seghdr) * * Throws error if request cannot be satisfied. * - * Assumes ShmemLock and ShmemSegHdr are initialized. + * Assumes ShmemSegHdr are initialized. */ void * ShmemAlloc(Size size) @@ -259,7 +257,7 @@ ShmemAllocRaw(Size size, Size *allocated_size) Assert(ShmemSegHdr != NULL); - SpinLockAcquire(ShmemLock); + SpinLockAcquire(&ShmemAllocator->shmem_lock); newStart = ShmemAllocator->free_offset; @@ -272,7 +270,7 @@ ShmemAllocRaw(Size size, Size *allocated_size) else newSpace = NULL; - SpinLockRelease(ShmemLock); + SpinLockRelease(&ShmemAllocator->shmem_lock); /* note this assert is okay with newSpace == NULL */ Assert(newSpace == (void *) CACHELINEALIGN(newSpace)); diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index 2e3f2f2a6ff..4c01afce2f7 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -191,6 +191,8 @@ typedef struct LWLockTrancheShmemData } user_defined[MAX_USER_DEFINED_TRANCHES]; int num_user_defined; /* 'user_defined' entries in use */ + + slock_t lock; /* protects the above */ } LWLockTrancheShmemData; LWLockTrancheShmemData *LWLockTranches; @@ -437,6 +439,7 @@ CreateLWLocks(void) ShmemAlloc(sizeof(LWLockTrancheShmemData)); /* Initialize the dynamic-allocation counter for tranches */ + SpinLockInit(&LWLockTranches->lock); LWLockTranches->num_user_defined = 0; /* Allocate and initialize the main array */ @@ -522,9 +525,9 @@ GetNamedLWLockTranche(const char *tranche_name) { int i; - SpinLockAcquire(ShmemLock); + SpinLockAcquire(&LWLockTranches->lock); LocalNumUserDefinedTranches = LWLockTranches->num_user_defined; - SpinLockRelease(ShmemLock); + SpinLockRelease(&LWLockTranches->lock); /* * Obtain the position of base address of LWLock belonging to requested @@ -576,14 +579,13 @@ LWLockNewTrancheId(const char *name) NAMEDATALEN - 1))); /* - * We use the ShmemLock spinlock to protect the counter and the tranche - * names. + * We use the spinlock to protect the counter and the tranche names. */ - SpinLockAcquire(ShmemLock); + SpinLockAcquire(&LWLockTranches->lock); if (LWLockTranches->num_user_defined >= MAX_USER_DEFINED_TRANCHES) { - SpinLockRelease(ShmemLock); + SpinLockRelease(&LWLockTranches->lock); ereport(ERROR, (errmsg("maximum number of tranches already registered"), errdetail("No more than %d tranches may be registered.", @@ -602,7 +604,7 @@ LWLockNewTrancheId(const char *name) /* the locks are not in the main array */ LWLockTranches->user_defined[idx].main_array_idx = -1; - SpinLockRelease(ShmemLock); + SpinLockRelease(&LWLockTranches->lock); return LWTRANCHE_FIRST_USER_DEFINED + idx; } @@ -712,14 +714,14 @@ GetLWTrancheName(uint16 trancheId) * lookups can avoid taking the spinlock as long as the backend-local * counter (LocalNumUserDefinedTranches) is greater than the requested * tranche ID. Else, we need to first update the backend-local counter - * with ShmemLock held before attempting the lookup again. In practice, - * the latter case is probably rare. + * with the spinlock held before attempting the lookup again. In + * practice, the latter case is probably rare. */ if (idx >= LocalNumUserDefinedTranches) { - SpinLockAcquire(ShmemLock); + SpinLockAcquire(&LWLockTranches->lock); LocalNumUserDefinedTranches = LWLockTranches->num_user_defined; - SpinLockRelease(ShmemLock); + SpinLockRelease(&LWLockTranches->lock); if (idx >= LocalNumUserDefinedTranches) elog(ERROR, "tranche %d is not registered", trancheId); diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h index 0de8a36429b..2a9e9becd26 100644 --- a/src/include/storage/shmem.h +++ b/src/include/storage/shmem.h @@ -26,7 +26,6 @@ /* shmem.c */ -extern PGDLLIMPORT slock_t *ShmemLock; typedef struct PGShmemHeader PGShmemHeader; /* avoid including * storage/pg_shmem.h here */ extern void InitShmemAllocator(PGShmemHeader *seghdr); -- 2.47.3