src/channel.c

@@ -23,7 +23,7 @@ void channel_add(jack_client_t *client, int idx)
         return;
     }
 
-    channels[idx].active = 1;
+    atomic_store(&channels[idx].active, 1);
     atomic_store(&channels[idx].state, STATE_IDLE);
     channels[idx].prev_state = -1;
     channels[idx].loop_count = 0;
@@ -38,6 +38,6 @@ void channel_remove(jack_client_t *client, int idx)
 {
     jack_port_unregister(client, channels[idx].audio_in);
     jack_port_unregister(client, channels[idx].audio_out);
-    channels[idx].active = 0;
+    atomic_store(&channels[idx].active, 0);
     channel_count--;
 }

src/channel.h

@@ -21,7 +21,7 @@ struct channel_t {
     int           loop_count;
     int           record_pos;
     int           playback_pos;
-    int           active;
+    atomic_int    active;
     jack_port_t  *audio_in;
     jack_port_t  *audio_out;
 };

src/looper.c

@@ -26,14 +26,16 @@ int process_callback(jack_nframes_t nframes, void *arg)
 {
     (void)arg;
 
+    if (midi_control_port) {
         void *midi_ctrl_buf = jack_port_get_buffer(midi_control_port, nframes);
         if (midi_ctrl_buf) {
             midi_handle_events(midi_ctrl_buf, nframes);
         }
+    }
 
     /* process each active channel */
     for (int c = 0; c < MAX_CHANNELS; c++) {
-        if (!channels[c].active) continue;
+        if (!atomic_load(&channels[c].active)) continue;
 
         /* Guard against NULL ports (e.g. if port registration failed) */
         if (!channels[c].audio_in || !channels[c].audio_out) {
@@ -108,6 +110,7 @@ int process_callback(jack_nframes_t nframes, void *arg)
     }
 
     /* MIDI clock events – affect channel 0 only */
+    if (midi_clock_port) {
         void *midi_clock_buf = jack_port_get_buffer(midi_clock_port, nframes);
         if (midi_clock_buf) {
             jack_nframes_t n_clock_events = jack_midi_get_event_count(midi_clock_buf);
@@ -136,6 +139,7 @@ int process_callback(jack_nframes_t nframes, void *arg)
                 }
             }
         }
+    }
 
     return 0;
 }

tests/integration.c

@@ -34,6 +34,7 @@ static unsigned char midi_inject_velocity = 0;
 
 static int midi_inject_process(jack_nframes_t nframes, void *arg) {
     (void)arg;
+    if (!midi_inject_port) return 0;
     void *port_buf = jack_port_get_buffer(midi_inject_port, nframes);
     if (!port_buf) return 0;
     jack_midi_clear_buffer(port_buf);