From eb0498bb28612760e3ba4016bba21a3bc03bb542 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Wed, 8 Sep 2021 21:50:57 +0200
Subject: [PATCH] Overhaul ambiguous latency detection

Simply comparing connected latency min/max is insufficient
and allows for false positives.

get_connected_latency_range() reports private, uncompensated
latency for internal ports. In this case an additional test
is required to match it against the reported latency of
connected ports.

Since 13b8a9727bb05 remote connected ports now correctly
report latency for both internal as well as external ports.
---
 libs/ardour/port_manager.cc | 51 +++++++++++++++++++++++++++++++++----
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index cc7d688cf4..90934b085d 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -1680,7 +1680,8 @@ PortManager::check_for_ambiguous_latency (bool log) const
 	boost::shared_ptr<Ports> plist = _ports.reader();
 	for (Ports::iterator pi = plist->begin(); pi != plist->end(); ++pi) {
 		boost::shared_ptr<Port> const& p (pi->second);
-		if (! p->sends_output () || (p->flags () & IsTerminal)) {
+		/* check one to many connections on the receiving side */
+		if (p->sends_output () || (p->flags () & IsTerminal)) {
 			continue;
 		}
 		if (boost::dynamic_pointer_cast<AsyncMIDIPort>(p)) {
@@ -1688,11 +1689,51 @@ PortManager::check_for_ambiguous_latency (bool log) const
 		}
 		assert (port_is_mine (p->name ()));
 
-		LatencyRange range;
-		p->get_connected_latency_range (range, true);
-		if (range.min != range.max) {
+		LatencyRange rangeA;
+		p->get_connected_latency_range (rangeA, true);
+
+		if (rangeA.min == rangeA.max) {
+			continue;
+		}
+
+		/* check if latency-range of connected ports matches our own */
+
+		vector<string> connections;
+		p->get_connections (connections);
+
+		assert (!connections.empty());
+
+		for (vector<string>::const_iterator c = connections.begin(); c != connections.end(); ++c) {
+			LatencyRange rangeB;
+
+			if (!AudioEngine::instance()->port_is_mine (*c)) {
+				PortEngine::PortHandle ph = _backend->get_port_by_name (*c);
+				if (!ph) {
+					continue;
+				}
+				rangeB = _backend->get_latency_range (ph, true);
+			} else {
+				Ports::iterator x = plist->find (make_port_name_relative (*c));
+				if (x == plist->end()) {
+					continue;
+				}
+				boost::shared_ptr<Port> const& pb (x->second);
+				if (pb->flags () & (IsTerminal | Hidden | TransportSyncPort)) {
+					continue;
+				}
+				pb->get_connected_latency_range (rangeB, true);
+			}
+
+			if (rangeA == rangeB) {
+				continue;
+			}
 			if (log) {
-				warning << string_compose(_("Ambiguous latency for port '%1' (%2, %3)"), p->name(), range.min, range.max) << endmsg;
+				warning << string_compose(
+						_("Ambiguous latency for input '%1' (%2, %3),"
+							"receiving from port '%4' (%5, %6)"),
+						p->name(), rangeA.min, rangeA.max,
+						*c, rangeB.min, rangeB.max)
+					<< endmsg;
 				rv = true;
 			} else {
 				return true;