From ef4bbae02e194e9f254b7d31918b25aadc46c1ae Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Wed, 1 Jun 2022 16:26:51 +0200
Subject: [PATCH] Fix logic in nth_mixer_scene (amend 00bd313e6e03)

_mixer_scenes[nth] may not exist, size check condition needs
to happen first. Writer lock is only required when changing the
vector.
---
 libs/ardour/session.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 512a3499b1..feb6dd246e 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -7525,7 +7525,10 @@ boost::shared_ptr<MixerScene>
 Session::nth_mixer_scene (size_t nth, bool create_if_missing)
 {
 	Glib::Threads::RWLock::ReaderLock lm (_mixer_scenes_lock);
-	if (create_if_missing && (!_mixer_scenes[nth] || _mixer_scenes.size() <= nth) ) {
+	if (create_if_missing) {
+		if (_mixer_scenes.size() > nth && _mixer_scenes[nth]) {
+			return _mixer_scenes[nth];
+		}
 		lm.release ();
 		Glib::Threads::RWLock::WriterLock lw (_mixer_scenes_lock);
 		if (_mixer_scenes.size() <= nth) {