From: Christopher Faulet <cfaulet@haproxy.com>
Date: Thu, 16 Oct 2025 09:37:54 +0000 (+0200)
Subject: EXP: peers: Use try-lock operations when looping on the updates list
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=165a33e015565c55944958490e8b449083ade841;p=thirdparty%2Fhaproxy.git

EXP: peers: Use try-lock operations when looping on the updates list
---

diff --git a/src/peers.c b/src/peers.c
index ab230d43c..94584aec2 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1549,7 +1549,6 @@ int peer_send_teachmsgs(struct appctx *appctx, struct peer *p, struct shared_tab
 	int ret, new_pushed, use_timed;
 	int updates_sent = 0;
 	struct stksess *ts = NULL;
-	struct mt_list back;
 
 	TRACE_ENTER(PEERS_EV_SESS_IO, appctx, p, st);
 
@@ -1562,79 +1561,69 @@ int peer_send_teachmsgs(struct appctx *appctx, struct peer *p, struct shared_tab
 	/* We force new pushed to 1 to force identifier in update message */
 	new_pushed = 1;
 
-	MT_LIST_FOR_EACH_ENTRY_LOCKED(ts, &st->last->upd, upd, back) {
-		if (ts == st->end) {
-			ret = 1; // done
+	while (1) {
+		struct mt_list el1, el2;
+
+		if (st->last->upd.next == &st->end->upd || st->last->upd.next == &st->table->updates)
+			break;
+
+		if (buffer_almost_full(&appctx->outbuf)) {
+			applet_have_more_data(appctx);
+			ret = -1;
 			break;
 		}
 
-		if (!(p->flags & PEER_F_TEACH_PROCESS) && ts->updt_type != STKSESS_UPDT_LOCAL)
-			continue;
-		else if (ts->updt_type != STKSESS_UPDT_LOCAL && ts->updt_type != STKSESS_UPDT_REMOTE)
+		if (updates_sent >= peers_max_updates_at_once) {
+			applet_have_more_data(appctx);
+			ret = -1;
+			break;
+		}
+
+		el1 = mt_list_try_lock_full(&st->last->upd);
+		if (el1.prev == NULL) {
+			applet_have_more_data(appctx);
+			ret = -1;
+			break;
+		}
+		el2 = mt_list_lock_next(el1.next);
+		/* el2 = mt_list_try_lock_next(el1.next); */
+		/* if (el2.next == NULL) { */
+		/* 	mt_list_unlock_full(&st->last->upd, el1); */
+		/* 	applet_have_more_data(appctx); */
+		/* 	ret = -1; */
+		/* 	break; */
+		/* } */
+
+		ts = MT_LIST_ELEM(el1.next, typeof(ts), upd);
+		HA_ATOMIC_INC(&ts->ref_cnt);
+
+		mt_list_unlock_full(&st->last->upd, el2);
+		mt_list_unlock_link(el1);
+
+		if ((!(p->flags & PEER_F_TEACH_PROCESS) && ts->updt_type != STKSESS_UPDT_LOCAL) ||
+		    (ts->updt_type != STKSESS_UPDT_LOCAL && ts->updt_type != STKSESS_UPDT_REMOTE) ||
+		    (p->srv->shard && ts->shard != p->srv->shard) ||
+		    ts->updt_type == STKSESS_UPDT_MARKER) {
+			HA_ATOMIC_DEC(&ts->ref_cnt);
 			continue;
+		}
 
 		if (st != p->last_local_table) {
 			ret = peer_send_switchmsg(st, appctx);
-			if (ret <= 0)
+			if (ret <= 0) {
+				HA_ATOMIC_DEC(&ts->ref_cnt);
 				break;
-
+			}
 			p->last_local_table = st;
 		}
 
 		if (!_HA_ATOMIC_LOAD(&ts->seen))
 			_HA_ATOMIC_STORE(&ts->seen, 1);
 
-		if (p->srv->shard && ts->shard != p->srv->shard)
-			continue;
-
-		if (updates_sent >= peers_max_updates_at_once) {
-			applet_have_more_data(appctx);
-			ret = -1;
-		}
-		else {
-			HA_ATOMIC_INC(&ts->ref_cnt);
-			ret = peer_send_updatemsg(st, appctx, ts, st->update_id, new_pushed, use_timed);
-			HA_ATOMIC_DEC(&ts->ref_cnt);
-		}
-
-		if (ret <= 0) {
-			/* Insert <last> marker before <ts> to process it again
-			 * on next iteration. <ts> remains locked
-			 *
-			 * Before:
-			 *           <back>: <A> <==============> <C>
-			 *
-			 *   <last> <==> ... <A> <==> x    x <==> <C> ...
-			 *
-			 *                       x <==> TS <==> x
-			 *
-			 *  <back>.prev == <A> and <back>.prev->next == MT_LIST_BUSY
-			 *
-			 *  Step 1: detach <last> from the list
-			 *  Step 2: insert <last> after <A>
-			 *           - <last>.prev = <A> (or <back>.prev)
-			 *           - <last>.next = MT_LIST_BUSY (or <back>.prev->next)
-			 *  Step 3: move <A> before <last>
-			 *           - <A>.next = <last> (or back.prev->next = <last>)
-			 *
-			 *  Step 4: update <back>.prev to point on <last>
-			 *
-			 *  After:
-			 *        <back>: <last> <==============> <C>
-			 *
-			 *   ... <A> <==> <last> <==> x    x <==> <C> ...
-			 *
-			 *                       x <==> TS <==> x
-			 *
-			 */
-			MT_LIST_DELETE(&st->last->upd);
-			st->last->upd.next = back.prev->next; /* == MT_LIST_BUSY */
-			__ha_barrier_atomic_store();
-			st->last->upd.prev = back.prev;
-			back.prev->next = &st->last->upd;
-			back.prev = &st->last->upd;
+		ret = peer_send_updatemsg(st, appctx, ts, st->update_id, new_pushed, use_timed);
+		HA_ATOMIC_DEC(&ts->ref_cnt);
+		if (ret <= 0)
 			break;
-		}
 
 		p->last.table = st;
 		p->last.id = st->update_id;
@@ -1647,12 +1636,9 @@ int peer_send_teachmsgs(struct appctx *appctx, struct peer *p, struct shared_tab
 		updates_sent++;
 	}
 
-	if (ret == 1) {
-		MT_LIST_DELETE(&st->last->upd);
-		MT_LIST_APPEND(&st->end->upd, &st->last->upd);
+	if (ret == 1)
 		MT_LIST_DELETE(&st->end->upd);
-	}
-
+  end:
 	TRACE_LEAVE(PEERS_EV_SESS_IO, appctx, p, st);
 	return ret;
 }