Add chainlock_read functions to get a read lock. Used in *massively*

contended tdb's (and I've got one :-).
Jeremy.
(This used to be commit d4b795e6a451d9abaa4a928cf5d34e12b2babc2d)

2 files changed, 50 insertions, 5 deletions

diff --git a/source3/tdb/tdb.c b/source3/tdb/tdb.c
index 2a6dca16a8..e539376ac7 100644
--- a/source3/tdb/tdb.c
+++ b/source3/tdb/tdb.c
@@ -186,7 +186,7 @@ static int tdb_brlock(TDB_CONTEXT *tdb, tdb_off offset,
 
 	if (tdb->flags & TDB_NOLOCK)
 		return 0;
-	if (tdb->read_only) {
+	if ((rw_type == F_WRLCK) && (tdb->read_only)) {
 		errno = EACCES;
 		return -1;
 	}
@@ -1802,6 +1802,16 @@ int tdb_chainunlock(TDB_CONTEXT *tdb, TDB_DATA key)
 	return tdb_unlock(tdb, BUCKET(tdb_hash(&key)), F_WRLCK);
 }
 
+int tdb_chainlock_read(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_lock(tdb, BUCKET(tdb_hash(&key)), F_RDLCK);
+}
+
+int tdb_chainunlock_read(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_unlock(tdb, BUCKET(tdb_hash(&key)), F_RDLCK);
+}
+
 
 /* register a loging function */
 void tdb_logging_function(TDB_CONTEXT *tdb, void (*fn)(TDB_CONTEXT *, int , const char *, ...))
diff --git a/source3/tdb/tdbutil.c b/source3/tdb/tdbutil.c
index ad97f45044..5498872f8a 100644
--- a/source3/tdb/tdbutil.c
+++ b/source3/tdb/tdbutil.c
@@ -39,7 +39,7 @@ static void gotalarm_sig(void)
  Lock a chain with timeout (in seconds).
 ****************************************************************************/
 
-int tdb_chainlock_with_timeout( TDB_CONTEXT *tdb, TDB_DATA key, unsigned int timeout)
+static int tdb_chainlock_with_timeout( TDB_CONTEXT *tdb, TDB_DATA key, unsigned int timeout, int rw_type)
 {
 	/* Allow tdb_chainlock to be interrupted by an alarm. */
 	int ret;
@@ -51,13 +51,19 @@ int tdb_chainlock_with_timeout( TDB_CONTEXT *tdb, TDB_DATA key, unsigned int tim
 		alarm(timeout);
 	}
 
-	ret = tdb_chainlock(tdb, key);
+	if (rw_type == F_RDLCK)
+		ret = tdb_chainlock_read(tdb, key);
+	else
+		ret = tdb_chainlock(tdb, key);
 
 	if (timeout) {
 		alarm(0);
 		CatchSignal(SIGALRM, SIGNAL_CAST SIG_IGN);
-		if (gotalarm)
+		if (gotalarm) {
+			DEBUG(0,("tdb_chainlock_with_timeout: alarm (%u) timed out for key %s in tdb %s\n",
+				timeout, key.dptr, tdb->name ));
 			return -1;
+		}
 	}
 
 	return ret;
@@ -74,7 +80,7 @@ int tdb_lock_bystring(TDB_CONTEXT *tdb, char *keyval, unsigned int timeout)
 	key.dptr = keyval;
 	key.dsize = strlen(keyval)+1;
 	
-	return tdb_chainlock_with_timeout(tdb, key, timeout);
+	return tdb_chainlock_with_timeout(tdb, key, timeout, F_WRLCK);
 }
 
 /****************************************************************************
@@ -92,6 +98,35 @@ void tdb_unlock_bystring(TDB_CONTEXT *tdb, char *keyval)
 }
 
 /****************************************************************************
+ Read lock a chain by string. Return -1 if timeout or lock failed.
+****************************************************************************/
+
+int tdb_read_lock_bystring(TDB_CONTEXT *tdb, char *keyval, unsigned int timeout)
+{
+	TDB_DATA key;
+
+	key.dptr = keyval;
+	key.dsize = strlen(keyval)+1;
+	
+	return tdb_chainlock_with_timeout(tdb, key, timeout, F_RDLCK);
+}
+
+/****************************************************************************
+ Read unlock a chain by string.
+****************************************************************************/
+
+void tdb_read_unlock_bystring(TDB_CONTEXT *tdb, char *keyval)
+{
+	TDB_DATA key;
+
+	key.dptr = keyval;
+	key.dsize = strlen(keyval)+1;
+	
+	tdb_chainunlock_read(tdb, key);
+}
+
+
+/****************************************************************************
  Fetch a int32 value by a arbitrary blob key, return -1 if not found.
  Output is int32 in native byte order.
 ****************************************************************************/