From 5cd9c86d580d6419400e67f5890d583c606c8a10 Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Thu, 17 Oct 2019 15:19:05 -0600
Subject: add RAII-style write protection while rendering MIDI playlist into
 RTMidiBuffer

---
 libs/ardour/ardour/rt_midibuffer.h | 13 ++++++++++++-
 libs/ardour/midi_playlist.cc       | 11 ++++++++++-
 libs/ardour/rt_midibuffer.cc       |  8 ++++++--
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/libs/ardour/ardour/rt_midibuffer.h b/libs/ardour/ardour/rt_midibuffer.h
index 5bb12afef9..ff17fd66e2 100644
--- a/libs/ardour/ardour/rt_midibuffer.h
+++ b/libs/ardour/ardour/rt_midibuffer.h
@@ -63,6 +63,7 @@ class LIBARDOUR_API RTMidiBuffer : public Evoral::EventSink<samplepos_t>
 	};
 
   private:
+	friend struct WriteProtectRender;
 
 	struct Blob {
 		uint32_t size;
@@ -85,7 +86,17 @@ class LIBARDOUR_API RTMidiBuffer : public Evoral::EventSink<samplepos_t>
 	uint32_t _pool_capacity;
 	uint8_t* _pool;
 
-	mutable Glib::Threads::RWLock _lock;
+	Glib::Threads::RWLock _lock;
+
+  public:
+	class WriteProtectRender {
+          public:
+		WriteProtectRender (RTMidiBuffer& rtm) : lm (rtm._lock, Glib::Threads::NOT_LOCK) {}
+		void acquire () { lm.acquire(); }
+
+          private:
+		Glib::Threads::RWLock::WriterLock lm;
+	};
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/midi_playlist.cc b/libs/ardour/midi_playlist.cc
index 61d114f67f..881641d32a 100644
--- a/libs/ardour/midi_playlist.cc
+++ b/libs/ardour/midi_playlist.cc
@@ -519,8 +519,12 @@ MidiPlaylist::render (RTMidiBuffer& dst, MidiChannelFilter* filter)
 	Evoral::EventList<samplepos_t>  evlist;
 	Evoral::EventSink<samplepos_t>* tgt;
 
+	/* RAII */
+	RTMidiBuffer::WriteProtectRender wpr (dst);
+
 	if (regs.size() == 1) {
 		tgt = &dst;
+		wpr.acquire ();
 	} else {
 		tgt = &evlist;
 	}
@@ -545,6 +549,9 @@ MidiPlaylist::render (RTMidiBuffer& dst, MidiChannelFilter* filter)
 		evlist.sort (cmp);
 
 		/* Copy ordered events from event list to dst. */
+
+		wpr.acquire ();
+
 		for (Evoral::EventList<samplepos_t>::iterator e = evlist.begin(); e != evlist.end(); ++e) {
 			Evoral::Event<samplepos_t>* ev (*e);
 			dst.write (ev->time(), ev->event_type(), ev->size(), ev->buffer());
@@ -552,6 +559,8 @@ MidiPlaylist::render (RTMidiBuffer& dst, MidiChannelFilter* filter)
 		}
 	}
 
-	DEBUG_TRACE (DEBUG::MidiPlaylistIO, "---- End MidiPlaylist::dump ----\n");
 
+	/* no need to release - RAII with WriteProtectRender takes care of it */
+
+	DEBUG_TRACE (DEBUG::MidiPlaylistIO, "---- End MidiPlaylist::dump ----\n");
 }
diff --git a/libs/ardour/rt_midibuffer.cc b/libs/ardour/rt_midibuffer.cc
index 29ac4c6fb9..7c1b1f5330 100644
--- a/libs/ardour/rt_midibuffer.cc
+++ b/libs/ardour/rt_midibuffer.cc
@@ -167,11 +167,15 @@ item_timestamp_earlier (ARDOUR::RTMidiBuffer::Item const & item, samplepos_t tim
 	return item.timestamp < time;
 }
 
-
-
 uint32_t
 RTMidiBuffer::read (MidiBuffer& dst, samplepos_t start, samplepos_t end, MidiStateTracker& tracker, samplecnt_t offset)
 {
+	Glib::Threads::RWLock::ReaderLock lm (_lock, Glib::Threads::TRY_LOCK);
+
+	if (!lm.locked()) {
+		return 0;
+	}
+
 	Item* iend = _data+_size;
 	Item* item = lower_bound (_data, iend, start, item_timestamp_earlier);
 	uint32_t count = 0;
-- 
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