From ce649cf851579992604ef81b40a1aaf904dbab1e Mon Sep 17 00:00:00 2001
From: Paul Licameli <paul.licameli@audacityteam.org>
Date: Sat, 23 Sep 2017 20:37:41 -0400
Subject: [PATCH] Re-enabling the separate MIDI thread, and comments about that

---
 src/AudioIO.cpp | 14 ++++++++++++--
 src/AudioIO.h   | 12 ++++++++----
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/AudioIO.cpp b/src/AudioIO.cpp
index 629bdce8e..a8d145dbc 100644
--- a/src/AudioIO.cpp
+++ b/src/AudioIO.cpp
@@ -441,8 +441,14 @@ writing audio.
 
 #ifdef EXPERIMENTAL_MIDI_OUT
    #define MIDI_SLEEP 10 /* milliseconds */
-   // how long do we think the thread might be delayed due to other threads?
-   #define THREAD_LATENCY 10 /* milliseconds */
+   // how long do we think the thread that fills MIDI buffers,
+   // if it is separate from the portaudio thread,
+   // might be delayed due to other threads?
+   #ifdef USE_MIDI_THREAD
+      #define THREAD_LATENCY 10 /* milliseconds */
+   #else
+      #define THREAD_LATENCY 0 /* milliseconds */
+   #endif
    #define ROUND(x) (int) ((x)+0.5)
    //#include <string.h>
    #include "../lib-src/portmidi/pm_common/portmidi.h"
@@ -4987,6 +4993,8 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
                if ((gAudioIO->ReversedTime()
                   ? gAudioIO->mTime <= gAudioIO->mT1
                   : gAudioIO->mTime >= gAudioIO->mT1))
+                  // PRL: singalling MIDI output complete is necessary if
+                  // not USE_MIDI_THREAD, otherwise it's harmlessly redundant
                   gAudioIO->mMidiOutputComplete = true,
                   callbackReturn = paComplete;
             }
@@ -5048,6 +5056,8 @@ int audacityAudioCallback(const void *inputBuffer, void *outputBuffer,
                ? gAudioIO->mTime <= gAudioIO->mT1
                : gAudioIO->mTime >= gAudioIO->mT1)) {
 
+               // PRL: singalling MIDI output complete is necessary if
+               // not USE_MIDI_THREAD, otherwise it's harmlessly redundant
                gAudioIO->mMidiOutputComplete = true,
                callbackReturn = paComplete;
             }
diff --git a/src/AudioIO.h b/src/AudioIO.h
index 506232d62..40e997ed0 100644
--- a/src/AudioIO.h
+++ b/src/AudioIO.h
@@ -93,11 +93,15 @@ DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_AUDIOIO_PLAYBACK, -1);
 DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_AUDIOIO_CAPTURE, -1);
 DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_AUDIOIO_MONITOR, -1);
 
+// PRL:
 // If we always run a portaudio output stream (even just to produce silence)
-// whenever we play Midi, then we can use just one thread for both, which
-// simplifies synchronization problems and avoids the rush of notes at start of
-// play.  PRL.
-#undef USE_MIDI_THREAD
+// whenever we play Midi, then we might use just one thread for both.
+// I thought this would improve MIDI synch problems on Linux/ALSA, but RBD
+// convinced me it was neither a necessary nor sufficient fix.  Perhaps too the
+// MIDI thread might block in some error situations but we should then not
+// also block the audio thread.
+// So leave the separate thread ENABLED.
+#define USE_MIDI_THREAD
 
 struct ScrubbingOptions;