From 1c61f20ae4bf45d1f918819ffd2f92efedc39448 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Sat, 21 Mar 2026 13:07:28 +0200 Subject: [PATCH v9 02/16] refactor: Move ShmemInitHash to separate file In preparation for next commits --- src/backend/storage/ipc/Makefile | 1 + src/backend/storage/ipc/meson.build | 1 + src/backend/storage/ipc/shmem.c | 77 ---------------------- src/backend/storage/ipc/shmem_hash.c | 98 ++++++++++++++++++++++++++++ src/include/storage/shmem.h | 1 + 5 files changed, 101 insertions(+), 77 deletions(-) create mode 100644 src/backend/storage/ipc/shmem_hash.c diff --git a/src/backend/storage/ipc/Makefile b/src/backend/storage/ipc/Makefile index 9a07f6e1d92..f71653bbe48 100644 --- a/src/backend/storage/ipc/Makefile +++ b/src/backend/storage/ipc/Makefile @@ -22,6 +22,7 @@ OBJS = \ shm_mq.o \ shm_toc.o \ shmem.o \ + shmem_hash.o \ signalfuncs.o \ sinval.o \ sinvaladt.o \ diff --git a/src/backend/storage/ipc/meson.build b/src/backend/storage/ipc/meson.build index 9c1ca954d9d..b8c31e29967 100644 --- a/src/backend/storage/ipc/meson.build +++ b/src/backend/storage/ipc/meson.build @@ -14,6 +14,7 @@ backend_sources += files( 'shm_mq.c', 'shm_toc.c', 'shmem.c', + 'shmem_hash.c', 'signalfuncs.c', 'sinval.c', 'sinvaladt.c', diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c index 0e49debaaac..1485f1ff38f 100644 --- a/src/backend/storage/ipc/shmem.c +++ b/src/backend/storage/ipc/shmem.c @@ -100,7 +100,6 @@ typedef struct ShmemAllocatorData #define ShmemIndexLock (&ShmemAllocator->index_lock) -static void *ShmemHashAlloc(Size size, void *alloc_arg); static void *ShmemAllocRaw(Size size, Size *allocated_size); /* shared memory global variables */ @@ -235,15 +234,6 @@ ShmemAllocNoError(Size size) return ShmemAllocRaw(size, &allocated_size); } -/* Alloc callback for shared memory hash tables */ -static void * -ShmemHashAlloc(Size size, void *alloc_arg) -{ - Size allocated_size; - - return ShmemAllocRaw(size, &allocated_size); -} - /* * ShmemAllocRaw -- allocate align chunk and return allocated size * @@ -305,73 +295,6 @@ ShmemAddrIsValid(const void *addr) return (addr >= ShmemBase) && (addr < ShmemEnd); } -/* - * ShmemInitHash -- Create and initialize, or attach to, a - * shared memory hash table. - * - * We assume caller is doing some kind of synchronization - * so that two processes don't try to create/initialize the same - * table at once. (In practice, all creations are done in the postmaster - * process; child processes should always be attaching to existing tables.) - * - * max_size is the estimated maximum number of hashtable entries. This is - * not a hard limit, but the access efficiency will degrade if it is - * exceeded substantially (since it's used to compute directory size and - * the hash table buckets will get overfull). - * - * init_size is the number of hashtable entries to preallocate. For a table - * whose maximum size is certain, this should be equal to max_size; that - * ensures that no run-time out-of-shared-memory failures can occur. - * - * *infoP and hash_flags must specify at least the entry sizes and key - * comparison semantics (see hash_create()). Flag bits and values specific - * to shared-memory hash tables are added here, except that callers may - * choose to specify HASH_PARTITION and/or HASH_FIXED_SIZE. - * - * Note: before Postgres 9.0, this function returned NULL for some failure - * cases. Now, it always throws error instead, so callers need not check - * for NULL. - */ -HTAB * -ShmemInitHash(const char *name, /* table string name for shmem index */ - int64 init_size, /* initial table size */ - int64 max_size, /* max size of the table */ - HASHCTL *infoP, /* info about key and bucket size */ - int hash_flags) /* info about infoP */ -{ - bool found; - void *location; - - /* - * Hash tables allocated in shared memory have a fixed directory; it can't - * grow or other backends wouldn't be able to find it. So, make sure we - * make it big enough to start with. - * - * The shared memory allocator must be specified too. - */ - infoP->dsize = infoP->max_dsize = hash_select_dirsize(max_size); - infoP->alloc = ShmemHashAlloc; - infoP->alloc_arg = NULL; - hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE; - - /* look it up in the shmem index */ - location = ShmemInitStruct(name, - hash_get_shared_size(infoP, hash_flags), - &found); - - /* - * if it already exists, attach to it rather than allocate and initialize - * new space - */ - if (found) - hash_flags |= HASH_ATTACH; - - /* Pass location of hashtable header to hash_create */ - infoP->hctl = (HASHHDR *) location; - - return hash_create(name, init_size, infoP, hash_flags); -} - /* * ShmemInitStruct -- Create/attach to a structure in shared memory. * diff --git a/src/backend/storage/ipc/shmem_hash.c b/src/backend/storage/ipc/shmem_hash.c new file mode 100644 index 00000000000..47166ff301d --- /dev/null +++ b/src/backend/storage/ipc/shmem_hash.c @@ -0,0 +1,98 @@ +/*------------------------------------------------------------------------- + * + * shmem_hash.c + * hash table implementation in shared memory + * + * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * A shared memory hash table implementation on top of the named, fixed-size + * shared memory areas managed by shmem.c. Hash tables have a fixed maximum + * size, but their actual size can vary dynamically. When entries are added + * to the table, more space is allocated. Each shared data structure and hash + * has a string name to identify it. + * + * IDENTIFICATION + * src/backend/storage/ipc/shmem_hash.c + * + *------------------------------------------------------------------------- + */ + +#include "postgres.h" + +#include "storage/shmem.h" + + +/* + * ShmemInitHash -- Create and initialize, or attach to, a + * shared memory hash table. + * + * We assume caller is doing some kind of synchronization + * so that two processes don't try to create/initialize the same + * table at once. (In practice, all creations are done in the postmaster + * process; child processes should always be attaching to existing tables.) + * + * max_size is the estimated maximum number of hashtable entries. This is + * not a hard limit, but the access efficiency will degrade if it is + * exceeded substantially (since it's used to compute directory size and + * the hash table buckets will get overfull). + * + * init_size is the number of hashtable entries to preallocate. For a table + * whose maximum size is certain, this should be equal to max_size; that + * ensures that no run-time out-of-shared-memory failures can occur. + * + * *infoP and hash_flags must specify at least the entry sizes and key + * comparison semantics (see hash_create()). Flag bits and values specific + * to shared-memory hash tables are added here, except that callers may + * choose to specify HASH_PARTITION and/or HASH_FIXED_SIZE. + * + * Note: before Postgres 9.0, this function returned NULL for some failure + * cases. Now, it always throws error instead, so callers need not check + * for NULL. + */ +HTAB * +ShmemInitHash(const char *name, /* table string name for shmem index */ + int64 init_size, /* initial table size */ + int64 max_size, /* max size of the table */ + HASHCTL *infoP, /* info about key and bucket size */ + int hash_flags) /* info about infoP */ +{ + bool found; + void *location; + + /* + * Hash tables allocated in shared memory have a fixed directory; it can't + * grow or other backends wouldn't be able to find it. So, make sure we + * make it big enough to start with. + * + * The shared memory allocator must be specified too. + */ + infoP->dsize = infoP->max_dsize = hash_select_dirsize(max_size); + infoP->alloc = ShmemHashAlloc; + infoP->alloc_arg = NULL; + hash_flags |= HASH_SHARED_MEM | HASH_ALLOC | HASH_DIRSIZE; + + /* look it up in the shmem index */ + location = ShmemInitStruct(name, + hash_get_shared_size(infoP, hash_flags), + &found); + + /* + * if it already exists, attach to it rather than allocate and initialize + * new space + */ + if (found) + hash_flags |= HASH_ATTACH; + + /* Pass location of hashtable header to hash_create */ + infoP->hctl = (HASHHDR *) location; + + return hash_create(name, init_size, infoP, hash_flags); +} + +/* Alloc callback for shared memory hash tables */ +void * +ShmemHashAlloc(Size size, void *alloc_arg) +{ + return ShmemAllocNoError(size); +} diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h index 2a9e9becd26..d26206131d7 100644 --- a/src/include/storage/shmem.h +++ b/src/include/storage/shmem.h @@ -31,6 +31,7 @@ typedef struct PGShmemHeader PGShmemHeader; /* avoid including extern void InitShmemAllocator(PGShmemHeader *seghdr); extern void *ShmemAlloc(Size size); extern void *ShmemAllocNoError(Size size); +extern void *ShmemHashAlloc(Size size, void *alloc_arg); extern bool ShmemAddrIsValid(const void *addr); extern HTAB *ShmemInitHash(const char *name, int64 init_size, int64 max_size, HASHCTL *infoP, int hash_flags); -- 2.47.3