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Modify ShmemInitStruct and ShmemInitHash to throw errors internally,

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rather than returning NULL for some-but-not-all failures as they used to.
Remove now-redundant tests for NULL from call sites.

We had to do something about this because many call sites were failing to
check for NULL; and changing it like this seems a lot more useful and
mistake-proof than adding checks to the call sites without them.
This commit is contained in:
Tom Lane
2010-04-28 16:54:16 +00:00
parent 5f70a04c56
commit 77acab75df
12 changed files with 87 additions and 112 deletions
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81
src/backend/storage/ipc/shmem.c
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@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.103 2010/01/02 16:57:51 momjian Exp $
* $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.104 2010/04/28 16:54:16 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -213,13 +213,13 @@ InitShmemIndex(void)
int hash_flags;
/*
* Create the shared memory shmem index.
*
* Since ShmemInitHash calls ShmemInitStruct, which expects the ShmemIndex
* hashtable to exist already, we have a bit of a circularity problem in
* initializing the ShmemIndex itself. The special "ShmemIndex" hash
* table name will tell ShmemInitStruct to fake it.
*/
/* create the shared memory shmem index */
info.keysize = SHMEM_INDEX_KEYSIZE;
info.entrysize = sizeof(ShmemIndexEnt);
hash_flags = HASH_ELEM;
@@ -227,8 +227,6 @@ InitShmemIndex(void)
ShmemIndex = ShmemInitHash("ShmemIndex",
SHMEM_INDEX_SIZE, SHMEM_INDEX_SIZE,
&info, hash_flags);
if (!ShmemIndex)
elog(FATAL, "could not initialize Shmem Index");
}
/*
@@ -236,8 +234,9 @@ InitShmemIndex(void)
* shared memory hash table.
*
* We assume caller is doing some kind of synchronization
* so that two people don't try to create/initialize the
* table at once.
* 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
@@ -247,6 +246,10 @@ InitShmemIndex(void)
* 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.
*
* 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 */
@@ -274,13 +277,6 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
hash_get_shared_size(infoP, hash_flags),
&found);
/*
* If fail, shmem index is corrupted. Let caller give the error message
* since it has more information
*/
if (location == NULL)
return NULL;
/*
* if it already exists, attach to it rather than allocate and initialize
* new space
@@ -295,18 +291,20 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
}
/*
* ShmemInitStruct -- Create/attach to a structure in shared
* memory.
* ShmemInitStruct -- Create/attach to a structure in shared memory.
*
* This is called during initialization to find or allocate
* This is called during initialization to find or allocate
* 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.
* structure is returned.
*
* Returns: real pointer to the object. FoundPtr is TRUE if
* the object is already in the shmem index (hence, already
* initialized).
* Returns: pointer to the object. *foundPtr is set TRUE if the object was
* already in the shmem index (hence, already initialized).
*
* 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.
*/
void *
ShmemInitStruct(const char *name, Size size, bool *foundPtr)
@@ -320,7 +318,9 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
{
PGShmemHeader *shmemseghdr = ShmemSegHdr;
/* Must be trying to create/attach to ShmemIndex itself */
Assert(strcmp(name, "ShmemIndex") == 0);
if (IsUnderPostmaster)
{
/* Must be initializing a (non-standalone) backend */
@@ -340,6 +340,12 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
*/
Assert(shmemseghdr->index == NULL);
structPtr = ShmemAlloc(size);
if (structPtr == NULL)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("not enough shared memory for data structure"
" \"%s\" (%lu bytes requested)",
name, (unsigned long) size)));
shmemseghdr->index = structPtr;
*foundPtr = FALSE;
}
@@ -356,7 +362,8 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
LWLockRelease(ShmemIndexLock);
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of shared memory")));
errmsg("could not create ShmemIndex entry for data structure \"%s\"",
name)));
}
if (*foundPtr)
@@ -364,15 +371,17 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
/*
* Structure is in the shmem index so someone else has allocated it
* already. The size better be the same as the size we are trying to
* initialize to or there is a name conflict (or worse).
* initialize to, or there is a name conflict (or worse).
*/
if (result->size != size)
{
LWLockRelease(ShmemIndexLock);
elog(WARNING, "ShmemIndex entry size is wrong");
/* let caller print its message too */
return NULL;
ereport(ERROR,
(errmsg("ShmemIndex entry size is wrong for data structure"
" \"%s\": expected %lu, actual %lu",
name,
(unsigned long) size,
(unsigned long) result->size)));
}
structPtr = result->location;
}
@@ -380,26 +389,24 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
{
/* It isn't in the table yet. allocate and initialize it */
structPtr = ShmemAlloc(size);
if (!structPtr)
if (structPtr == NULL)
{
/* out of memory */
Assert(ShmemIndex);
/* out of memory; remove the failed ShmemIndex entry */
hash_search(ShmemIndex, name, HASH_REMOVE, NULL);
LWLockRelease(ShmemIndexLock);
ereport(WARNING,
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("could not allocate shared memory segment \"%s\"",
name)));
*foundPtr = FALSE;
return NULL;
errmsg("not enough shared memory for data structure"
" \"%s\" (%lu bytes requested)",
name, (unsigned long) size)));
}
result->size = size;
result->location = structPtr;
}
Assert(ShmemAddrIsValid(structPtr));
LWLockRelease(ShmemIndexLock);
Assert(ShmemAddrIsValid(structPtr));
return structPtr;
}