diff options
Diffstat (limited to 'src/backend/storage/ipc/shmem.c')
| -rw-r--r-- | src/backend/storage/ipc/shmem.c | 121 |
1 files changed, 67 insertions, 54 deletions
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c index e6865563b39..21d136d6cf0 100644 --- a/src/backend/storage/ipc/shmem.c +++ b/src/backend/storage/ipc/shmem.c @@ -8,25 +8,26 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.89 2005/12/29 18:08:05 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.90 2006/01/04 21:06:31 tgl Exp $ * *------------------------------------------------------------------------- */ /* * POSTGRES processes share one or more regions of shared memory. * The shared memory is created by a postmaster and is inherited - * by each backend via fork(). The routines in this file are used for - * allocating and binding to shared memory data structures. + * by each backend via fork() (or, in some ports, via other OS-specific + * methods). The routines in this file are used for allocating and + * binding to shared memory data structures. * * NOTES: * (a) There are three kinds of shared memory data structures * available to POSTGRES: fixed-size structures, queues and hash * tables. Fixed-size structures contain things like global variables - * for a module and should never be allocated after the process + * for a module and should never be allocated after the shared memory * initialization phase. 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. Queues link data structures - * that have been allocated either as fixed size structures or as hash + * that have been allocated either within fixed-size structures or as hash * buckets. Each shared data structure has a string name to identify * it (assigned in the module that declares it). * @@ -46,7 +47,14 @@ * of shared memory in a lot of different places (and changing * things during development), this is important. * - * (c) memory allocation model: shared memory can never be + * (c) In standard Unix-ish environments, individual backends do not + * need to re-establish their local pointers into shared memory, because + * they inherit correct values of those variables via fork() from the + * postmaster. However, this does not work in the EXEC_BACKEND case. + * In ports using EXEC_BACKEND, new backends have to set up their local + * pointers using the method described in (b) above. + + * (d) memory allocation model: shared memory can never be * freed, once allocated. Each hash table has its own free list, * so hash buckets can be reused when an item is deleted. However, * if one hash table grows very large and then shrinks, its space @@ -75,58 +83,59 @@ static SHMEM_OFFSET ShmemEnd; /* end+1 address of shared memory */ slock_t *ShmemLock; /* spinlock for shared memory and LWLock * allocation */ -NON_EXEC_STATIC slock_t *ShmemIndexLock; /* spinlock for ShmemIndex */ - -NON_EXEC_STATIC void *ShmemIndexAlloc = NULL; /* Memory actually allocated - * for ShmemIndex */ - static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */ /* - * InitShmemAllocation() --- set up shared-memory allocation. + * InitShmemAccess() --- set up basic pointers to shared memory. * * Note: the argument should be declared "PGShmemHeader *seghdr", * but we use void to avoid having to include ipc.h in shmem.h. */ void -InitShmemAllocation(void *seghdr, bool init) +InitShmemAccess(void *seghdr) { PGShmemHeader *shmhdr = (PGShmemHeader *) seghdr; - /* Set up basic pointers to shared memory */ ShmemSegHdr = shmhdr; ShmemBase = (SHMEM_OFFSET) shmhdr; ShmemEnd = ShmemBase + shmhdr->totalsize; +} - if (init) - { - /* - * Initialize the spinlocks used by ShmemAlloc/ShmemInitStruct. We - * have to do the space allocation the hard way, since ShmemAlloc - * can't be called yet. - */ - ShmemLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset); - shmhdr->freeoffset += MAXALIGN(sizeof(slock_t)); - Assert(shmhdr->freeoffset <= shmhdr->totalsize); +/* + * InitShmemAllocation() --- set up shared-memory space allocation. + * + * This should be called only in the postmaster or a standalone backend. + */ +void +InitShmemAllocation(void) +{ + PGShmemHeader *shmhdr = ShmemSegHdr; - ShmemIndexLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset); - shmhdr->freeoffset += MAXALIGN(sizeof(slock_t)); - Assert(shmhdr->freeoffset <= shmhdr->totalsize); + Assert(shmhdr != NULL); - SpinLockInit(ShmemLock); - SpinLockInit(ShmemIndexLock); + /* + * Initialize the spinlock used by ShmemAlloc. We have to do the + * space allocation the hard way, since obviously ShmemAlloc can't + * be called yet. + */ + ShmemLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset); + shmhdr->freeoffset += MAXALIGN(sizeof(slock_t)); + Assert(shmhdr->freeoffset <= shmhdr->totalsize); - /* ShmemIndex can't be set up yet (need LWLocks first) */ - ShmemIndex = (HTAB *) NULL; + SpinLockInit(ShmemLock); - /* - * Initialize ShmemVariableCache for transaction manager. - */ - ShmemVariableCache = (VariableCache) - ShmemAlloc(sizeof(*ShmemVariableCache)); - memset(ShmemVariableCache, 0, sizeof(*ShmemVariableCache)); - } + /* ShmemIndex can't be set up yet (need LWLocks first) */ + shmhdr->indexoffset = 0; + ShmemIndex = (HTAB *) NULL; + + /* + * Initialize ShmemVariableCache for transaction manager. + * (This doesn't really belong here, but not worth moving.) + */ + ShmemVariableCache = (VariableCache) + ShmemAlloc(sizeof(*ShmemVariableCache)); + memset(ShmemVariableCache, 0, sizeof(*ShmemVariableCache)); } /* @@ -194,7 +203,7 @@ ShmemIsValid(unsigned long addr) } /* - * InitShmemIndex() --- set up shmem index table. + * InitShmemIndex() --- set up or attach to shmem index table. */ void InitShmemIndex(void) @@ -239,15 +248,14 @@ InitShmemIndex(void) result->location = MAKE_OFFSET(ShmemIndex->hctl); result->size = SHMEM_INDEX_SIZE; - } /* now release the lock acquired in ShmemInitStruct */ - SpinLockRelease(ShmemIndexLock); + LWLockRelease(ShmemIndexLock); } /* - * ShmemInitHash -- Create/Attach to and initialize + * ShmemInitHash -- Create and initialize, or attach to, a * shared memory hash table. * * We assume caller is doing some kind of synchronization @@ -290,8 +298,8 @@ ShmemInitHash(const char *name, /* table string name for shmem index */ &found); /* - * shmem index is corrupted. Let someone else give the error message - * since they have more information + * If fail, shmem index is corrupted. Let caller give the error message + * since it has more information */ if (location == NULL) return NULL; @@ -315,8 +323,8 @@ ShmemInitHash(const char *name, /* table string name for shmem index */ * memory. * * This is called during initialization to find or allocate - * a data structure in shared memory. If no other processes - * have created the structure, this routine allocates space + * a data structure in shared memory. If no other process + * has created the structure, this routine allocates space * for it. If it exists already, a pointer to the existing * table is returned. * @@ -334,15 +342,18 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) strncpy(item.key, name, SHMEM_INDEX_KEYSIZE); item.location = BAD_LOCATION; - SpinLockAcquire(ShmemIndexLock); + LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE); if (!ShmemIndex) { + PGShmemHeader *shmemseghdr = ShmemSegHdr; + Assert(strcmp(name, "ShmemIndex") == 0); if (IsUnderPostmaster) { /* Must be initializing a (non-standalone) backend */ - Assert(ShmemIndexAlloc); + Assert(shmemseghdr->indexoffset != 0); + structPtr = (void *) MAKE_PTR(shmemseghdr->indexoffset); *foundPtr = TRUE; } else @@ -354,10 +365,12 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) * Notice that the ShmemIndexLock is held until the shmem index * has been completely initialized. */ + Assert(shmemseghdr->indexoffset == 0); + structPtr = ShmemAlloc(size); + shmemseghdr->indexoffset = MAKE_OFFSET(structPtr); *foundPtr = FALSE; - ShmemIndexAlloc = ShmemAlloc(size); } - return ShmemIndexAlloc; + return structPtr; } /* look it up in the shmem index */ @@ -366,7 +379,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) if (!result) { - SpinLockRelease(ShmemIndexLock); + LWLockRelease(ShmemIndexLock); ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); @@ -381,7 +394,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) */ if (result->size != size) { - SpinLockRelease(ShmemIndexLock); + LWLockRelease(ShmemIndexLock); elog(WARNING, "ShmemIndex entry size is wrong"); /* let caller print its message too */ @@ -398,7 +411,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) /* out of memory */ Assert(ShmemIndex); hash_search(ShmemIndex, (void *) &item, HASH_REMOVE, NULL); - SpinLockRelease(ShmemIndexLock); + LWLockRelease(ShmemIndexLock); ereport(WARNING, (errcode(ERRCODE_OUT_OF_MEMORY), @@ -411,7 +424,7 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr) } Assert(ShmemIsValid((unsigned long) structPtr)); - SpinLockRelease(ShmemIndexLock); + LWLockRelease(ShmemIndexLock); return structPtr; } |