status: suppress status_trace/status_debug messages if queue too long.

common/daemon_conn.c

@@ -146,3 +146,8 @@ void daemon_conn_wake(struct daemon_conn *dc)
 {
 	msg_wake(dc->out);
 }
+
+size_t daemon_conn_queue_length(const struct daemon_conn *dc)
+{
+	return msg_queue_length(dc->out);
+}

common/daemon_conn.h

@@ -56,4 +56,10 @@ struct io_plan *daemon_conn_read_next(struct io_conn *conn,
  * daemon_conn_sync_flush - Flush connection by sending all messages now..
  */
 bool daemon_conn_sync_flush(struct daemon_conn *dc);
+
+/**
+ * daemon_conn_queue_length - Get number of message in outgoing queue.
+ */
+size_t daemon_conn_queue_length(const struct daemon_conn *dc);
+
 #endif /* LIGHTNING_COMMON_DAEMON_CONN_H */

common/msg_queue.c

@@ -22,6 +22,11 @@ static void do_enqueue(struct msg_queue *q, const u8 *add TAKES)
 	io_wake(q);
 }
 
+size_t msg_queue_length(const struct msg_queue *q)
+{
+	return tal_count(q->q);
+}
+
 void msg_enqueue(struct msg_queue *q, const u8 *add)
 {
 	assert(fromwire_peektype(add) != MSG_PASS_FD);

common/msg_queue.h

@@ -15,6 +15,9 @@ struct msg_queue *msg_queue_new(const tal_t *ctx);
 /* If add is taken(), freed after sending.  msg_wake() implied. */
 void msg_enqueue(struct msg_queue *q, const u8 *add TAKES);
 
+/* Get current queue length */
+size_t msg_queue_length(const struct msg_queue *q);
+
 /* Fd is closed after sending.  msg_wake() implied. */
 void msg_enqueue_fd(struct msg_queue *q, int fd);
 

common/status.c

@@ -20,6 +20,10 @@ static struct daemon_conn *status_conn;
 volatile bool logging_io = false;
 static bool was_logging_io = false;
 
+/* If we're more than this many msgs deep, don't add debug messages. */
+#define TRACE_QUEUE_LIMIT 20
+static size_t traces_suppressed;
+
 static void got_sigusr1(int signal UNUSED)
 {
 	logging_io = !logging_io;
@@ -118,6 +122,22 @@ void status_vfmt(enum log_level level, const char *fmt, va_list ap)
 {
 	char *str;
 
+	/* We only suppress async debug msgs.  IO messages are even spammier
+	 * but they only occur when explicitly asked for */
+	if (level == LOG_DBG && status_conn) {
+		size_t qlen = daemon_conn_queue_length(status_conn);
+
+		/* Once suppressing, we keep suppressing until we're empty */
+		if (traces_suppressed && qlen == 0) {
+			size_t n = traces_suppressed;
+			traces_suppressed = 0;
+			/* Careful: recursion! */
+			status_debug("...[%zu debug messages suppressed]...", n);
+		} else if (traces_suppressed || qlen > TRACE_QUEUE_LIMIT) {
+			traces_suppressed++;
+			return;
+		}
+	}
 	str = tal_vfmt(NULL, fmt, ap);
 	status_send(take(towire_status_log(NULL, level, str)));
 	tal_free(str);