Modify ShmemInitStruct and ShmemInitHash to throw errors internally,

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.

contrib/pg_stat_statements/pg_stat_statements.c

@@ -14,7 +14,7 @@
  * Copyright (c) 2008-2010, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/contrib/pg_stat_statements/pg_stat_statements.c,v 1.13 2010/02/26 02:00:32 momjian Exp $
+ *	  $PostgreSQL: pgsql/contrib/pg_stat_statements/pg_stat_statements.c,v 1.14 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -321,8 +321,6 @@ pgss_shmem_startup(void)
 	pgss = ShmemInitStruct("pg_stat_statements",
 						   sizeof(pgssSharedState),
 						   &found);
-	if (!pgss)
-		elog(ERROR, "out of shared memory");
 
 	if (!found)
 	{
@@ -343,8 +341,6 @@ pgss_shmem_startup(void)
 							  pgss_max, pgss_max,
 							  &info,
 							  HASH_ELEM | HASH_FUNCTION | HASH_COMPARE);
-	if (!pgss_hash)
-		elog(ERROR, "out of shared memory");
 
 	LWLockRelease(AddinShmemInitLock);
 

doc/src/sgml/xfunc.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.145 2010/04/03 07:22:56 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.146 2010/04/28 16:54:15 tgl Exp $ -->
 
  <sect1 id="xfunc">
   <title>User-Defined Functions</title>
@@ -3350,8 +3350,6 @@ void RequestAddinLWLocks(int n)
 
                 LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
                 ptr = ShmemInitStruct("my struct name", size, &amp;found);
-                if (!ptr)
-                        elog(ERROR, "out of shared memory");
                 if (!found)
                 {
                         initialize contents of shmem area;

src/backend/access/transam/slru.c

@@ -41,7 +41,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.49 2010/02/16 22:34:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.50 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -164,8 +164,6 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 	shared = (SlruShared) ShmemInitStruct(name,
 										  SimpleLruShmemSize(nslots, nlsns),
 										  &found);
-	if (!shared)
-		elog(ERROR, "out of shared memory");
 
 	if (!IsUnderPostmaster)
 	{

src/backend/commands/async.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.156 2010/04/05 00:42:24 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.157 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -464,9 +464,6 @@ AsyncShmemInit(void)
 	asyncQueueControl = (AsyncQueueControl *)
 		ShmemInitStruct("Async Queue Control", size, &found);
 
-	if (!asyncQueueControl)
-		elog(ERROR, "out of shared memory");
-
 	if (!found)
 	{
 		/* First time through, so initialize it */

src/backend/postmaster/autovacuum.c

@@ -55,7 +55,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.109 2010/02/26 02:00:55 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.110 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2771,10 +2771,6 @@ AutoVacuumShmemInit(void)
 		ShmemInitStruct("AutoVacuum Data",
 						AutoVacuumShmemSize(),
 						&found);
-	if (AutoVacuumShmem == NULL)
-		ereport(FATAL,
-				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough shared memory for autovacuum")));
 
 	if (!IsUnderPostmaster)
 	{

src/backend/postmaster/bgwriter.c

@@ -38,7 +38,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.67 2010/02/05 23:37:43 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.68 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -890,16 +890,14 @@ BgWriterShmemInit(void)
 		ShmemInitStruct("Background Writer Data",
 						BgWriterShmemSize(),
 						&found);
-	if (BgWriterShmem == NULL)
-		ereport(FATAL,
-				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough shared memory for background writer")));
-	if (found)
-		return;					/* already initialized */
-
-	MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct));
-	SpinLockInit(&BgWriterShmem->ckpt_lck);
-	BgWriterShmem->max_requests = NBuffers;
+
+	if (!found)
+	{
+		/* First time through, so initialize */
+		MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct));
+		SpinLockInit(&BgWriterShmem->ckpt_lck);
+		BgWriterShmem->max_requests = NBuffers;
+	}
 }
 
 /*

src/backend/replication/walreceiverfuncs.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/replication/walreceiverfuncs.c,v 1.4 2010/02/26 02:00:57 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/replication/walreceiverfuncs.c,v 1.5 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -58,17 +58,13 @@ WalRcvShmemInit(void)
 	WalRcv = (WalRcvData *)
 		ShmemInitStruct("Wal Receiver Ctl", WalRcvShmemSize(), &found);
 
-	if (WalRcv == NULL)
-		ereport(FATAL,
-				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough shared memory for walreceiver")));
-	if (found)
-		return;					/* already initialized */
-
-	/* Initialize the data structures */
-	MemSet(WalRcv, 0, WalRcvShmemSize());
-	WalRcv->walRcvState = WALRCV_STOPPED;
-	SpinLockInit(&WalRcv->mutex);
+	if (!found)
+	{
+		/* First time through, so initialize */
+		MemSet(WalRcv, 0, WalRcvShmemSize());
+		WalRcv->walRcvState = WALRCV_STOPPED;
+		SpinLockInit(&WalRcv->mutex);
+	}
 }
 
 /* Is walreceiver in progress (or starting up)? */

src/backend/replication/walsender.c

@@ -30,7 +30,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.18 2010/04/28 16:10:42 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/replication/walsender.c,v 1.19 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -268,8 +268,7 @@ WalSndHandshake(void)
 						if (wal_level == WAL_LEVEL_MINIMAL)
 							ereport(FATAL,
 									(errcode(ERRCODE_CANNOT_CONNECT_NOW),
-									 errmsg("standby connections not allowed because wal_level='minimal'")));
-
+									 errmsg("standby connections not allowed because wal_level=\"minimal\"")));
 
 						/* Send a CopyOutResponse message, and start streaming */
 						pq_beginmessage(&buf, 'H');
@@ -838,21 +837,17 @@ WalSndShmemInit(void)
 	WalSndCtl = (WalSndCtlData *)
 		ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
 
-	if (WalSndCtl == NULL)
-		ereport(FATAL,
-				(errcode(ERRCODE_OUT_OF_MEMORY),
-				 errmsg("not enough shared memory for walsender")));
-	if (found)
-		return;					/* already initialized */
-
-	/* Initialize the data structures */
-	MemSet(WalSndCtl, 0, WalSndShmemSize());
-
-	for (i = 0; i < max_wal_senders; i++)
+	if (!found)
 	{
-		WalSnd	   *walsnd = &WalSndCtl->walsnds[i];
+		/* First time through, so initialize */
+		MemSet(WalSndCtl, 0, WalSndShmemSize());
+
+		for (i = 0; i < max_wal_senders; i++)
+		{
+			WalSnd	   *walsnd = &WalSndCtl->walsnds[i];
 
-		SpinLockInit(&walsnd->mutex);
+			SpinLockInit(&walsnd->mutex);
+		}
 	}
 }
 

src/backend/storage/buffer/buf_table.c

@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.51 2010/01/02 16:57:51 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.52 2010/04/28 16:54:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -66,9 +66,6 @@ InitBufTable(int size)
 								  size, size,
 								  &info,
 								  HASH_ELEM | HASH_FUNCTION | HASH_PARTITION);
-
-	if (!SharedBufHash)
-		elog(FATAL, "could not initialize shared buffer hash table");
 }
 
 /*

src/backend/storage/ipc/shmem.c

@@ -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: pointer to the object.  *foundPtr is set TRUE if the object was
+ *		already in the shmem index (hence, already initialized).
  *
- *	Returns: real pointer to the object.  FoundPtr is TRUE if
- *		the object is 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;
 }
 

src/backend/storage/lmgr/lock.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.196 2010/03/21 00:17:58 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.197 2010/04/28 16:54:16 tgl Exp $
  *
  * NOTES
  *	  A lock table is a shared memory hash table.  When
@@ -306,8 +306,6 @@ InitLocks(void)
 									   max_table_size,
 									   &info,
 									   hash_flags);
-	if (!LockMethodLockHash)
-		elog(FATAL, "could not initialize lock hash table");
 
 	/* Assume an average of 2 holders per lock */
 	max_table_size *= 2;
@@ -328,8 +326,6 @@ InitLocks(void)
 										   max_table_size,
 										   &info,
 										   hash_flags);
-	if (!LockMethodProcLockHash)
-		elog(FATAL, "could not initialize proclock hash table");
 
 	/*
 	 * Allocate non-shared hash table for LOCALLOCK structs.  This stores lock

src/backend/storage/lmgr/proc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.217 2010/02/26 02:01:01 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.218 2010/04/28 16:54:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -756,21 +756,22 @@ AuxiliaryProcKill(int code, Datum arg)
 /*
  * ProcQueueAlloc -- alloc/attach to a shared memory process queue
  *
- * Returns: a pointer to the queue or NULL
- * Side Effects: Initializes the queue if we allocated one
+ * Returns: a pointer to the queue
+ * Side Effects: Initializes the queue if it wasn't there before
  */
 #ifdef NOT_USED
 PROC_QUEUE *
-ProcQueueAlloc(char *name)
+ProcQueueAlloc(const char *name)
 {
+	PROC_QUEUE *queue;
 	bool		found;
-	PROC_QUEUE *queue = (PROC_QUEUE *)
-	ShmemInitStruct(name, sizeof(PROC_QUEUE), &found);
 
-	if (!queue)
-		return NULL;
+	queue = (PROC_QUEUE *)
+		ShmemInitStruct(name, sizeof(PROC_QUEUE), &found);
+
 	if (!found)
 		ProcQueueInit(queue);
+
 	return queue;
 }
 #endif