Check all delayed clients for a serviceable one in the connector when we can and consider dropping a client servicing one to not potentially create delayed sends faster than we service them

src/connector.c

@@ -466,17 +466,17 @@ void *sender(void *arg)
 	rename_proc("csender");
 
 	while (42) {
-		sender_send_t *sender_send;
+		sender_send_t *sender_send, *delayed;
 		client_instance_t *client;
-		int ret, fd, ofs = 0;
+		int ret = 0, fd, ofs = 0;
 
 		mutex_lock(&cdata->sender_lock);
-		/* Poll every 100ms if there are no new sends. Re-examine
+		/* Poll every 10ms if there are no new sends. Re-examine
 		 * delayed sends immediately after a successful send in case
 		 * endless new sends more frequently end up starving the
 		 * delayed sends. */
 		if (!cdata->sender_sends && !sent) {
-			const ts_t polltime = {0, 100000000};
+			const ts_t polltime = {0, 10000000};
 			ts_t timeout_ts;
 
 			ts_realtime(&timeout_ts);
@@ -494,23 +494,33 @@ void *sender(void *arg)
 		 * conditional with no new sends appearing or have just
 		 * serviced another message successfully. */
 		if (!sender_send) {
-			if (!cdata->delayed_sends)
-				continue;
+			/* Find a delayed client that needs servicing and set
+			 * ret accordingly. We do not need to use FOREACH_SAFE
+			 * as we break out of the loop as soon as we manipuate
+			 * the list. */
+			DL_FOREACH(cdata->delayed_sends, delayed) {
+				if ((ret = wait_write_select(delayed->client->fd, 0))) {
 					sender_send = cdata->delayed_sends;
 					DL_DELETE(cdata->delayed_sends, sender_send);
+					break;
+				}
+			}
+			/* None found ? */
+			if (!sender_send)
+				continue;
 		}
-
 		client = sender_send->client;
 
-		ck_rlock(&cdata->lock);
-		fd = client->fd;
-		ck_runlock(&cdata->lock);
-
 		/* If this socket is not ready to receive data from us, put the
 		 * send back on the tail of the list and decrease the timeout
 		 * to poll to either look for a client that is ready or poll
 		 * select on this one */
+		ck_rlock(&cdata->lock);
+		fd = client->fd;
+		if (!ret)
 			ret = wait_write_select(fd, 0);
+		ck_runlock(&cdata->lock);
+
 		if (ret < 1) {
 			if (ret < 0) {
 				LOGINFO("Client id %"PRId64" fd %d interrupted", client->id, fd);
@@ -526,7 +536,6 @@ void *sender(void *arg)
 			cdata->sends_delayed++;
 			continue;
 		}
-		sent = true;
 		while (sender_send->len) {
 			ret = send(fd, sender_send->buf + ofs, sender_send->len , 0);
 			if (unlikely(ret < 0)) {
@@ -538,6 +547,7 @@ void *sender(void *arg)
 			sender_send->len -= ret;
 		}
 contfree:
+		sent = true;
 		free(sender_send->buf);
 		free(sender_send);
 		dec_instance_ref(cdata, client);