From 078e652859238e425baca5a8bb5c7da8ad05086d Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Wed, 4 May 2022 02:10:46 +0200
Subject: [PATCH] Implement rt-safe deletion - delegate to butler

---
 libs/ardour/ardour/butler.h         |  8 ++++++
 libs/ardour/ardour/rt_safe_delete.h | 39 +++++++++++++++++++++++++++++
 libs/ardour/butler.cc               | 11 ++++++++
 libs/ardour/session.cc              |  1 +
 4 files changed, 59 insertions(+)
 create mode 100644 libs/ardour/ardour/rt_safe_delete.h

diff --git a/libs/ardour/ardour/butler.h b/libs/ardour/ardour/butler.h
index b6b11b4633..67e9818b6f 100644
--- a/libs/ardour/ardour/butler.h
+++ b/libs/ardour/ardour/butler.h
@@ -31,6 +31,7 @@
 #include "pbd/g_atomic_compat.h"
 #include "pbd/pool.h"
 #include "pbd/ringbuffer.h"
+#include "pbd/mpmc_queue.h"
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/session_handle.h"
@@ -62,6 +63,11 @@ public:
 
 	void map_parameters ();
 
+	bool delegate (sigc::slot<void> const& work) {
+		bool rv = _delegated_work.push_back (work);
+		summon ();
+		return rv;
+	}
 	samplecnt_t audio_capture_buffer_size () const
 	{
 		return _audio_capture_buffer_size;
@@ -92,6 +98,7 @@ private:
 	void* thread_work ();
 
 	void empty_pool_trash ();
+	void process_delegated_work ();
 	void config_changed (std::string);
 	bool flush_tracks_to_disk_normal (boost::shared_ptr<RouteList>, uint32_t& errors);
 	void queue_request (Request::Type r);
@@ -109,6 +116,7 @@ private:
 
 	PBD::RingBuffer<CrossThreadPool*> pool_trash;
 	CrossThreadChannel                _xthread;
+	PBD::MPMCQueue<sigc::slot<void> > _delegated_work;
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/ardour/rt_safe_delete.h b/libs/ardour/ardour/rt_safe_delete.h
new file mode 100644
index 0000000000..f848ea155f
--- /dev/null
+++ b/libs/ardour/ardour/rt_safe_delete.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2022 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include "ardour/audioengine.h"
+#include "ardour/butler.h"
+#include "ardour/session.h"
+
+namespace ARDOUR {
+
+template <class C>
+void rt_safe_delete (ARDOUR::Session* s, C* gc) {
+	if (s->deletion_in_progress () || !s->engine ().in_process_thread ()) {
+		delete gc;
+		return;
+	}
+	if (!s->butler ()->delegate (sigc::bind ([] (C* p) { delete p; }, gc))) {
+		delete gc;
+		return;
+	}
+}
+
+}
diff --git a/libs/ardour/butler.cc b/libs/ardour/butler.cc
index f16b3a0d5a..3def1e7740 100644
--- a/libs/ardour/butler.cc
+++ b/libs/ardour/butler.cc
@@ -327,6 +327,7 @@ Butler::thread_work ()
 
 		DEBUG_TRACE (DEBUG::Butler, "butler emptying pool trash\n");
 		empty_pool_trash ();
+		process_delegated_work ();
 	}
 
 	return (0);
@@ -464,11 +465,21 @@ Butler::empty_pool_trash ()
 	}
 }
 
+void
+Butler::process_delegated_work ()
+{
+	sigc::slot<void> sl;
+	while (_delegated_work.pop_front (sl)) {
+		sl ();
+	}
+}
+
 void
 Butler::drop_references ()
 {
 	std::cerr << "Butler drops pool trash\n";
 	SessionEvent::pool->set_trash (0);
+	process_delegated_work ();
 }
 
 } // namespace ARDOUR
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index b397ce90ab..bb546ab04b 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -104,6 +104,7 @@
 #include "ardour/route_graph.h"
 #include "ardour/route_group.h"
 #include "ardour/rt_tasklist.h"
+#include "ardour/rt_safe_delete.h"
 #include "ardour/silentfilesource.h"
 #include "ardour/send.h"
 #include "ardour/selection.h"