zynaddsubfx

commit fef41d030545862c9cb2018f72297e33018c791b
parent 98e0b77a1a543252307dffb4a32abb2f852c8618
Author: Hans Petter Selasky <hps@selasky.org>
Date:   Thu,  3 Oct 2019 20:15:05 +0200

Reduce number of system calls for ALSA MIDI by implementing proper polling.

Use polling with a timeout instead of polling for MIDI events thousands of
times per second with no timeout. This reduces the CPU usage for ZynAddSubFX.

Signed-off-by: Hans Petter Selasky <hps@selasky.org>

Diffstat:
M
src/Nio/AlsaEngine.cpp
 | 
28
+++++++++++++++++++++-------

1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/src/Nio/AlsaEngine.cpp b/src/Nio/AlsaEngine.cpp
@@ -14,6 +14,7 @@
 #include <stdlib.h>
 #include <iostream>
 #include <cmath>
+#include <poll.h>
 
 #include "../Misc/Util.h"
 #include "../Misc/Config.h"
@@ -105,17 +106,29 @@ void *AlsaEngine::_MidiThread(void *arg)
 void *AlsaEngine::MidiThread(void)
 {
     snd_seq_event_t *event;
-    MidiEvent ev;
+    MidiEvent ev = {};
+    struct pollfd pfd[4 /* XXX 1 should be enough */];
+    int error;
+
     set_realtime();
     while(1) {
         if(midi.exiting)
             break;
-        if(snd_seq_event_input_pending(midi.handle, 1) <= 0) {
-            usleep(10);
-            continue;
-        }
-        if(snd_seq_event_input(midi.handle, &event) < 0)
+        error = snd_seq_poll_descriptors(midi.handle, pfd, 4, POLLIN);
+        if(error <= 0)
             break;
+        error = poll(pfd, error, 1000 /* ms */);
+        if(error < 0) {
+          if(errno == EAGAIN || errno == EINTR)
+              continue;
+          break;
+        }
+        error = snd_seq_event_input(midi.handle, &event);
+        if (error < 0) {
+          if(error == -EAGAIN || error == -EINTR)
+              continue;
+          break;
+        }
         //ensure ev is empty
         ev.channel = 0;
         ev.num     = 0;
@@ -228,7 +241,8 @@ bool AlsaEngine::openMidi()
     int alsaport;
     midi.handle = NULL;
 
-    if(snd_seq_open(&midi.handle, "default", SND_SEQ_OPEN_INPUT, 0) != 0)
+    if(snd_seq_open(&midi.handle, "default",
+       SND_SEQ_OPEN_INPUT, SND_SEQ_NONBLOCK) != 0)
         return false;
 
     string clientname = "ZynAddSubFX";