diff options
Diffstat (limited to 'src/backend/storage/buffer/buf_table.c')
| -rw-r--r-- | src/backend/storage/buffer/buf_table.c | 38 |
1 files changed, 24 insertions, 14 deletions
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c index ef79ae9c393..7fe9e83477c 100644 --- a/src/backend/storage/buffer/buf_table.c +++ b/src/backend/storage/buffer/buf_table.c @@ -3,12 +3,9 @@ * buf_table.c * routines for mapping BufferTags to buffer indexes. * - * NOTE: this module is called only by freelist.c, and the "buffer IDs" - * it deals with are whatever freelist.c needs them to be; they may not be - * directly equivalent to Buffer numbers. - * - * Note: all routines in this file assume that the BufMgrLock is held - * by the caller, so no synchronization is needed. + * Note: the routines in this file do no locking of their own. The caller + * must hold a suitable lock on the BufMappingLock, as specified in the + * comments. * * * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group @@ -16,7 +13,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.39 2005/02/03 23:29:11 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/storage/buffer/buf_table.c,v 1.40 2005/03/04 20:21:06 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -74,17 +71,17 @@ InitBufTable(int size) /* * BufTableLookup * Lookup the given BufferTag; return buffer ID, or -1 if not found + * + * Caller must hold at least share lock on BufMappingLock */ int BufTableLookup(BufferTag *tagPtr) { BufferLookupEnt *result; - if (tagPtr->blockNum == P_NEW) - return -1; - result = (BufferLookupEnt *) hash_search(SharedBufHash, (void *) tagPtr, HASH_FIND, NULL); + if (!result) return -1; @@ -93,14 +90,23 @@ BufTableLookup(BufferTag *tagPtr) /* * BufTableInsert - * Insert a hashtable entry for given tag and buffer ID + * Insert a hashtable entry for given tag and buffer ID, + * unless an entry already exists for that tag + * + * Returns -1 on successful insertion. If a conflicting entry exists + * already, returns the buffer ID in that entry. + * + * Caller must hold write lock on BufMappingLock */ -void +int BufTableInsert(BufferTag *tagPtr, int buf_id) { BufferLookupEnt *result; bool found; + Assert(buf_id >= 0); /* -1 is reserved for not-in-table */ + Assert(tagPtr->blockNum != P_NEW); /* invalid tag */ + result = (BufferLookupEnt *) hash_search(SharedBufHash, (void *) tagPtr, HASH_ENTER, &found); @@ -109,15 +115,19 @@ BufTableInsert(BufferTag *tagPtr, int buf_id) (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); - if (found) /* found something already in the table? */ - elog(ERROR, "shared buffer hash table corrupted"); + if (found) /* found something already in the table */ + return result->id; result->id = buf_id; + + return -1; } /* * BufTableDelete * Delete the hashtable entry for given tag (which must exist) + * + * Caller must hold write lock on BufMappingLock */ void BufTableDelete(BufferTag *tagPtr) |