gossipd: single-thread the gossip timer.

We have a function called 'wake_pkt_out' which is really 'start
gossiping', so rename it to 'wake_gossip_out'.

In addition, it's fired both on a timer, and in response to our first
gossip_timestamp_filter, which leads to very confusing (though,
technically, not incorrect) behavior.

Keep a single timer at all times, which now doubles as the flag to
indicating we're syncing right now.  Set it once we're done syncing
gossip.

Technically this means we got from once-every-60-seconds to
quiet-for-60-seconds-between-gossip, but that's OK.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/gossip.c

@@ -228,8 +228,8 @@ struct peer {
 	struct pubkey *scid_query_nodes;
 	size_t scid_query_nodes_idx;
 
-	/* Is it time to continue the staggered broadcast? */
+	/* If this is NULL, we're syncing gossip now. */
-	bool gossip_sync;
+	struct oneshot *gossip_timer;
 
 	/* How many query responses are we expecting? */
 	size_t num_scid_queries_outstanding;
@@ -252,7 +252,6 @@ struct addrhint {
 static struct io_plan *peer_start_gossip(struct io_conn *conn,
 					 struct peer *peer);
 static bool send_peer_with_fds(struct peer *peer, const u8 *msg);
-static void wake_pkt_out(struct peer *peer);
 static void retry_important(struct important_peerid *imp);
 
 static void destroy_peer(struct peer *peer)
@@ -349,6 +348,7 @@ static struct peer *new_peer(const tal_t *ctx,
 	peer->addr = *addr;
 	peer->daemon = daemon;
 	peer->local = new_local_peer_state(peer, cs);
+	peer->gossip_timer = NULL;
 	peer->remote = NULL;
 	peer->scid_queries = NULL;
 	peer->scid_query_idx = 0;
@@ -448,6 +448,19 @@ static void queue_peer_msg(struct peer *peer, const u8 *msg TAKES)
 	}
 }
 
+static void wake_gossip_out(struct peer *peer)
+{
+	/* If we were waiting, we're not any more */
+	peer->gossip_timer = tal_free(peer->gossip_timer);
+
+	if (peer->local)
+		/* Notify the peer-write loop */
+		msg_wake(&peer->local->peer_out);
+	else if (peer->remote)
+		/* Notify the daemon_conn-write loop */
+		msg_wake(&peer->remote->out);
+}
+
 static void peer_error(struct peer *peer, const char *fmt, ...)
 {
 	va_list ap;
@@ -588,7 +601,7 @@ static struct io_plan *peer_connected(struct io_conn *conn, struct peer *peer)
 		return io_close(conn);
 
 	/* Start the gossip flowing. */
-	wake_pkt_out(peer);
+	wake_gossip_out(peer);
 
 	setup_gossip_range(peer);
 	return io_close_taken_fd(conn);
@@ -887,7 +900,7 @@ static void handle_gossip_timestamp_filter(struct peer *peer, u8 *msg)
 
 	/* First time, start gossip sync immediately. */
 	if (peer->gossip_timestamp_min > peer->gossip_timestamp_max)
-		wake_pkt_out(peer);
+		wake_gossip_out(peer);
 
 	/* FIXME: We don't index by timestamp, so this forces a brute
 	 * search! */
@@ -1088,26 +1101,6 @@ static struct io_plan *peer_msgin(struct io_conn *conn,
 	return peer_next_in(conn, peer);
 }
 
-/* Wake up the outgoing direction of the connection and write any
- * queued messages. Needed since the `io_wake` method signature does
- * not allow us to specify it as the callback for `new_reltimer`, but
- * it allows us to set an additional flag for the routing dump..
- */
-static void wake_pkt_out(struct peer *peer)
-{
-	peer->gossip_sync = true;
-	new_reltimer(&peer->daemon->timers, peer,
-		     time_from_msec(peer->daemon->broadcast_interval),
-		     wake_pkt_out, peer);
-
-	if (peer->local)
-		/* Notify the peer-write loop */
-		msg_wake(&peer->local->peer_out);
-	else if (peer->remote)
-		/* Notify the daemon_conn-write loop */
-		msg_wake(&peer->remote->out);
-}
-
 /* Mutual recursion. */
 static struct io_plan *peer_pkt_out(struct io_conn *conn, struct peer *peer);
 
@@ -1246,7 +1239,7 @@ static bool maybe_queue_gossip(struct peer *peer)
 {
 	const u8 *next;
 
-	if (!peer->gossip_sync)
+	if (peer->gossip_timer)
 		return false;
 
 	next = next_broadcast(peer->daemon->rstate->broadcasts,
@@ -1260,7 +1253,10 @@ static bool maybe_queue_gossip(struct peer *peer)
 	}
 
 	/* Gossip is drained.  Wait for next timer. */
-	peer->gossip_sync = false;
+	peer->gossip_timer
+		= new_reltimer(&peer->daemon->timers, peer,
+			       time_from_msec(peer->daemon->broadcast_interval),
+			       wake_gossip_out, peer);
 	return false;
 }
 
@@ -1296,7 +1292,7 @@ again:
 /* Now we're a fully-fledged peer. */
 static struct io_plan *peer_start_gossip(struct io_conn *conn, struct peer *peer)
 {
-	wake_pkt_out(peer);
+	wake_gossip_out(peer);
 	return io_duplex(conn,
 			 peer_next_in(conn, peer),
 			 peer_pkt_out(conn, peer));