From f3e13848fa6f773b3f4cb75649d38bf8fa21861f Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Fri, 7 Apr 2023 19:37:30 +0200
Subject: [PATCH] Do not modify read-only RCU copy of routelist

RCU reader returns a shared ptr to the current object which
can also be used in other places at the same time.

Sorting the shared-ptr list invalidates iterators which can
throw off other users of the same object.

This fixes a bug in PT-import which calls get_nth_audio_track().
---
 libs/ardour/session.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index be2106049c..57354bb8ef 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -6408,11 +6408,11 @@ Session::route_removed_from_route_group (RouteGroup* rg, std::weak_ptr<Route> r)
 std::shared_ptr<AudioTrack>
 Session::get_nth_audio_track (uint32_t nth) const
 {
-	std::shared_ptr<RouteList> rl = routes.reader ();
-	rl->sort (Stripable::Sorter ());
+	RouteList rl (*(routes.reader ()));
+	rl.sort (Stripable::Sorter());
 
-	for (RouteList::const_iterator r = rl->begin(); r != rl->end(); ++r) {
-		std::shared_ptr<AudioTrack> at = std::dynamic_pointer_cast<AudioTrack> (*r);
+	for (auto const& r: rl) {
+		std::shared_ptr<AudioTrack> at = std::dynamic_pointer_cast<AudioTrack> (r);
 		if (!at) {
 			continue;
 		}