From 4e1291a83f61a72989045879763d9ef05fd38f71 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Tue, 21 Dec 1999 09:25:59 +0000
Subject: converted all our existing shared memory code to use a tdb database
 instead of either sysv or mmap shared memory or lock files.

this means we can now completely remove
	locking_shm.c
	locking_slow.c
	shmem.c
	shmem_sysv.c
and lots of other things also got simpler

locking.c got a bit larger, but is much better compartmentalised now
(This used to be commit e48c2d9937eea0667b8cd3332e49c06314ef31e7)
---
 source3/tdb/tdb.c | 65 +++++++++++++++++++++++++++++--------------------------
 1 file changed, 34 insertions(+), 31 deletions(-)

(limited to 'source3/tdb')

diff --git a/source3/tdb/tdb.c b/source3/tdb/tdb.c
index 01d2e740f7..70880b5345 100644
--- a/source3/tdb/tdb.c
+++ b/source3/tdb/tdb.c
@@ -75,6 +75,26 @@ static char *memdup(char *d, int size)
 }
 #endif
 
+
+/* a byte range locking function - return 0 on success
+   this functions locks/unlocks 1 byte at the specified offset */
+static int tdb_brlock(TDB_CONTEXT *tdb, tdb_off offset, int set)
+{
+#if !NOLOCK
+	struct flock fl;
+
+	fl.l_type = set?F_WRLCK:F_UNLCK;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = offset;
+	fl.l_len = 1;
+	fl.l_pid = 0;
+
+	if (fcntl(tdb->fd, F_SETLKW, &fl) != 0) return -1;
+#endif
+	return 0;
+}
+
+
 /* the hash algorithm - turn a key into an integer
    This is based on the hash agorithm from gdbm */
 static unsigned tdb_hash(TDB_DATA *key)
@@ -991,42 +1011,25 @@ int tdb_close(TDB_CONTEXT *tdb)
 /* lock the database. If we already have it locked then don't do anything */
 int tdb_writelock(TDB_CONTEXT *tdb)
 {
-#if !NOLOCK
-	struct flock fl;
-
-	if (tdb->write_locked) return 0;
-
-	fl.l_type = F_WRLCK;
-	fl.l_whence = SEEK_SET;
-	fl.l_start = 0;
-	fl.l_len = 1;
-	fl.l_pid = 0;
-
-	if (fcntl(tdb->fd, F_SETLKW, &fl) != 0) return -1;
-
-	tdb->write_locked = 1;
-#endif
-	return 0;
+	return tdb_brlock(tdb, 0, 1);
 }
 
-/* unlock the database. If we don't have it locked then return -1 */
+/* unlock the database. */
 int tdb_writeunlock(TDB_CONTEXT *tdb)
 {
-#if !NOLOCK
-	struct flock fl;
-
-	if (!tdb->write_locked) return -1;
+	return tdb_brlock(tdb, 0, 0);
+}
 
-	fl.l_type = F_UNLCK;
-	fl.l_whence = SEEK_SET;
-	fl.l_start = 0;
-	fl.l_len = 1;
-	fl.l_pid = 0;
+/* lock one hash chain. This is meant to be used to reduce locking
+   contention - it cannot guarantee how many records will be locked */
+int tdb_lockchain(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_brlock(tdb, tdb_hash_top(tdb, tdb_hash(&key)), 1);
+}
 
-	if (fcntl(tdb->fd, F_SETLK, &fl) != 0) return -1;
 
-	tdb->write_locked = 0;
-#endif
-	return 0;
+/* unlock one hash chain */
+int tdb_unlockchain(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_brlock(tdb, tdb_hash_top(tdb, tdb_hash(&key)), 0);
 }
-
-- 
cgit