Drain ALSA raw-midi buffers after 64 bytes

Very long sequence of *concurrent* events may otherwise be truncated
because the backend requests a buffer-size of 64 bytes via
snd_rawmidi_params_set_buffer_size().

diff --git a/libs/backends/alsa/alsa_rawmidi.cc b/libs/backends/alsa/alsa_rawmidi.cc
index 0702c63158c8bb94f1ae32f6076058c6fabfb831..8d2420a6cbd357a77303126577be2298df89ac27 100644 (file)
--- a/libs/backends/alsa/alsa_rawmidi.cc
+++ b/libs/backends/alsa/alsa_rawmidi.cc
@@ -88,7 +88,7 @@ AlsaRawMidiIO::init (const char *device_name, const bool input)
        if (snd_rawmidi_params_set_avail_min (_device, params, 1)) {
                goto initerr;
        }
-       if ( snd_rawmidi_params_set_buffer_size (_device, params, 64)) {
+       if (snd_rawmidi_params_set_buffer_size (_device, params, 64)) {
                goto initerr;
        }
        if (snd_rawmidi_params_set_no_active_sensing (_device, params, 1)) {
@@ -119,7 +119,7 @@ AlsaRawMidiOut::main_process_thread ()
 {
        _running = true;
        pthread_mutex_lock (&_notify_mutex);
-       bool need_drain = false;
+       unsigned int need_drain = 0;
        while (_running) {
                bool have_data = false;
                struct MidiEventHeader h(0,0);
@@ -146,9 +146,9 @@ AlsaRawMidiOut::main_process_thread ()
                }
 
                if (!have_data) {
-                       if (need_drain) {
+                       if (need_drain > 0) {
                                snd_rawmidi_drain (_device);
-                               need_drain = false;
+                               need_drain = 0;
                        }
                        pthread_cond_wait (&_notify_ready, &_notify_mutex);
                        continue;
@@ -156,9 +156,9 @@ AlsaRawMidiOut::main_process_thread ()
 
                uint64_t now = g_get_monotonic_time();
                while (h.time > now + 500) {
-                       if (need_drain) {
+                       if (need_drain > 0) {
                                snd_rawmidi_drain (_device);
-                               need_drain = false;
+                               need_drain = 0;
                        } else {
                                select_sleep(h.time - now);
                        }
@@ -195,6 +195,14 @@ retry:
 
                ssize_t err = snd_rawmidi_write (_device, data, h.size);
 
+#if 0 // DEBUG -- not rt-safe
+               printf("TX [%ld | %ld]", h.size, err);
+               for (size_t i = 0; i < h.size; ++i) {
+                       printf (" %02x", data[i]);
+               }
+               printf ("\n");
+#endif
+
                if ((err == -EAGAIN)) {
                        snd_rawmidi_drain (_device);
                        goto retry;
@@ -213,7 +221,11 @@ retry:
                        h.size -= err;
                        goto retry;
                }
-               need_drain = true;
+
+               if ((need_drain += h.size) >= 64) {
+                       snd_rawmidi_drain (_device);
+                       need_drain = 0;
+               }
        }
 
        pthread_mutex_unlock (&_notify_mutex);