Fix for a problem with the new messaging system. If a sender is using the

messaging system as a notification mechanism, and the speed of notification
greatly exceeds the speed of message recovery, then you get a massively (>75Mb)
growing tdb. If the message is a simple notification, then the message is
static, and you only need one of them in transit to a target process at
any one time.
This patch adds a BOOL "allow_duplicates" to the message_send_XX primitives.
If set to False, then before sending a message the sender checks the existing
message queue for a target pid for a duplicate of this message, and doesn't
add to it if one already exists.
Also added code into msgtest.c to test this.
Jeremy.

source/lib/messages.c

@@ -71,7 +71,7 @@ a useful function for testing the message system
 void ping_message(int msg_type, pid_t src, void *buf, size_t len)
 {
 	DEBUG(1,("INFO: Received PING message from PID %d\n",src));
-	message_send_pid(src, MSG_PONG, buf, len);
+	message_send_pid(src, MSG_PONG, buf, len, True);
 }
 
 /****************************************************************************
@@ -83,7 +83,7 @@ void debuglevel_message(int msg_type, pid_t src, void *buf, size_t len)
 	
 	DEBUG(1,("INFO: Received REQ_DEBUGLEVEL message from PID %d\n",src));
         level = DEBUGLEVEL;
-	message_send_pid(src, MSG_DEBUGLEVEL, &level, sizeof(int));
+	message_send_pid(src, MSG_DEBUGLEVEL, &level, sizeof(int), True);
 }
 
 /****************************************************************************
@@ -148,13 +148,23 @@ static BOOL message_notify(pid_t pid)
 /****************************************************************************
 send a message to a particular pid
 ****************************************************************************/
-BOOL message_send_pid(pid_t pid, int msg_type, void *buf, size_t len)
+BOOL message_send_pid(pid_t pid, int msg_type, void *buf, size_t len, BOOL duplicates_allowed)
 {
 	TDB_DATA kbuf;
 	TDB_DATA dbuf;
 	struct message_rec rec;
 	void *p;
 
+	/*
+	 * Do an early check for process exists - saves adding into a tdb
+	 * and deleting again if the target is not present. JRA.
+	 */
+
+	if (kill(pid, 0) == -1) {
+		DEBUG(2,("message_send_pid: pid %d doesn't exist\n", (int)pid));
+		return False;
+	}
+
 	rec.msg_version = MESSAGE_VERSION;
 	rec.msg_type = msg_type;
 	rec.dest = pid;
@@ -183,6 +193,30 @@ BOOL message_send_pid(pid_t pid, int msg_type, void *buf, size_t len)
 		goto ok;
 	}
 
+	if (!duplicates_allowed) {
+		char *ptr;
+		struct message_rec *prec;
+		
+		for(ptr = (char *)dbuf.dptr, prec = (struct message_rec *)ptr; ptr < dbuf.dptr + dbuf.dsize;
+					ptr += (sizeof(rec) + prec->len), prec = (struct message_rec *)ptr) {
+
+			/*
+			 * First check if the message header matches, then, if it's a non-zero
+			 * sized message, check if the data matches. If so it's a duplicate and
+			 * we can discard it. JRA.
+			 */
+
+			if (!memcmp(ptr, &rec, sizeof(rec))) {
+				if (!len || (len && !memcmp( ptr + sizeof(rec), (char *)buf, len))) {
+					DEBUG(10,("message_send_pid: discarding duplicate message.\n"));
+					free(dbuf.dptr);
+					tdb_unlockchain(tdb, kbuf);
+					return True;
+				}
+			}
+		}
+	}
+
 	/* we're adding to an existing entry */
 	p = (void *)malloc(dbuf.dsize + len + sizeof(rec));
 	if (!p) goto failed;
@@ -323,6 +357,7 @@ static struct {
 	int msg_type;
 	void *buf;
 	size_t len;
+	BOOL duplicates;
 } msg_all;
 
 /****************************************************************************
@@ -335,7 +370,7 @@ static int traverse_fn(TDB_CONTEXT *the_tdb, TDB_DATA kbuf, TDB_DATA dbuf, void
 	memcpy(&crec, dbuf.dptr, sizeof(crec));
 
 	if (crec.cnum == -1) return 0;
-	message_send_pid(crec.pid, msg_all.msg_type, msg_all.buf, msg_all.len);
+	message_send_pid(crec.pid, msg_all.msg_type, msg_all.buf, msg_all.len, msg_all.duplicates);
 	return 0;
 }
 
@@ -344,7 +379,7 @@ this is a useful function for sending messages to all smbd processes.
 It isn't very efficient, but should be OK for the sorts of applications that 
 use it. When we need efficient broadcast we can add it.
 ****************************************************************************/
-BOOL message_send_all(int msg_type, void *buf, size_t len)
+BOOL message_send_all(int msg_type, void *buf, size_t len, BOOL duplicates_allowed)
 {
 	TDB_CONTEXT *the_tdb;
 
@@ -357,6 +392,7 @@ BOOL message_send_all(int msg_type, void *buf, size_t len)
 	msg_all.msg_type = msg_type;
 	msg_all.buf = buf;
 	msg_all.len = len;
+	msg_all.duplicates = duplicates_allowed;
 
 	tdb_traverse(the_tdb, traverse_fn, NULL);
 	tdb_close(the_tdb);