feat: unify add/remove commands into queue and fix race on channel removal

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/command.h

@@ -4,10 +4,10 @@
 typedef enum {
     CMD_CYCLE,          // toggle record/stop for a channel
     CMD_STOP,           // force to idle
-    // CMD_LOOP_TOGGLE not needed, CYCLE covers it
     CMD_BIND_CHANNEL,   // bind a channel index (data = channel)
     CMD_UNBIND,         // reset bind to channel 0
-    // ADD and REMOVE are still driven via atomics for now
+    CMD_ADD_CHANNEL,    // add a new dynamic channel
+    CMD_REMOVE_CHANNEL, // remove last dynamic channel
 } cmd_type_t;
 
 typedef struct {

src/looper.c

@@ -16,16 +16,17 @@
 struct channel_t channels[MAX_CHANNELS];
 atomic_int channel_count = 0;
 int next_channel_id = 1;
-atomic_int cmd_add = 0;
-atomic_int cmd_remove = 0;
+spsc_queue_t cmd_queue_main;
+atomic_int global_rt_cycles = 0;
 jack_port_t *midi_control_port = NULL;
 jack_port_t *midi_clock_port = NULL;
 atomic_int control_key_active = 0;
 atomic_int bind_channel = 0;
 spsc_queue_t cmd_queue;
 
-/* Deferred removal index (1 second grace) */
+/* Deferred removal index and cycle counter */
 static int pending_unregister_idx = -1;
+static int pending_unregister_cycle = 0;
 
 static void apply_command(command_t cmd) {
     switch (cmd.type) {
@@ -199,6 +200,7 @@ int process_callback(jack_nframes_t nframes, void *arg) {
     }
   }
 
+  atomic_fetch_add_explicit(&global_rt_cycles, 1, memory_order_release);
   return 0;
 }
 
@@ -216,6 +218,7 @@ void jack_shutdown_cb(void *arg) {
  * ---------------------------------------------------------------- */
 int looper_init(jack_client_t *client) {
   queue_init(&cmd_queue);
+  queue_init(&cmd_queue_main);
   /* channel 0 */
   channels[0].active = 1;
   atomic_store(&channels[0].state, STATE_IDLE);
@@ -250,10 +253,40 @@ int looper_init(jack_client_t *client) {
  * main‑loop command processing
  * ---------------------------------------------------------------- */
 void looper_process_commands(jack_client_t *client) {
-  /* Unregister any ports that were marked for deferred removal.
-     By now the real‑time thread has had at least one full cycle
-     to see the `active = 0` store. */
+  /* Drain main‑loop command queue (add/remove) */
+  command_t cmd;
+  while (queue_pop(&cmd_queue_main, &cmd)) {
+    switch (cmd.type) {
+    case CMD_ADD_CHANNEL: {
+      int idx;
+      for (idx = 0; idx < MAX_CHANNELS; idx++)
+        if (!channels[idx].active)
+          break;
+      if (idx < MAX_CHANNELS)
+        channel_add(client, idx);
+      break;
+    }
+    case CMD_REMOVE_CHANNEL: {
+      int remove_idx = -1;
+      for (int idx = 1; idx < MAX_CHANNELS; idx++)
+        if (channels[idx].active)
+          remove_idx = idx;
+      if (remove_idx != -1) {
+        channel_remove(client, remove_idx);
+        pending_unregister_idx = remove_idx;
+        pending_unregister_cycle = atomic_load(&global_rt_cycles);
+      }
+      break;
+    }
+    default:
+      break;
+    }
+  }
+
+  /* Deferred port unregistration – wait until RT thread has seen active=0 */
   if (pending_unregister_idx != -1) {
+    int current_cycle = atomic_load(&global_rt_cycles);
+    if (current_cycle - pending_unregister_cycle >= 1) {
       int idx = pending_unregister_idx;
       if (channels[idx].audio_in)
         jack_port_unregister(client, channels[idx].audio_in);
@@ -261,26 +294,5 @@ void looper_process_commands(jack_client_t *client) {
         jack_port_unregister(client, channels[idx].audio_out);
       pending_unregister_idx = -1;
     }
-
-  if (atomic_exchange(&cmd_add, 0)) {
-    int idx;
-    for (idx = 0; idx < MAX_CHANNELS; idx++)
-      if (!channels[idx].active)
-        break;
-    if (idx < MAX_CHANNELS) {
-      channel_add(client, idx);
-    }
-  }
-
-  if (atomic_exchange(&cmd_remove, 0)) {
-    int remove_idx = -1;
-    for (int idx = 1; idx < MAX_CHANNELS; idx++)
-      if (channels[idx].active)
-        remove_idx = idx;
-    if (remove_idx != -1) {
-      /* Mark inactive now; ports will be unregistered next round */
-      channel_remove(client, remove_idx);
-      pending_unregister_idx = remove_idx;
-    }
   }
 }

src/midi.c

@@ -8,10 +8,9 @@
 #include <stdatomic.h>
 
 extern atomic_int control_key_active;
-extern atomic_int cmd_add;
-extern atomic_int cmd_remove;
 extern atomic_int bind_channel;
 extern spsc_queue_t cmd_queue;
+extern spsc_queue_t cmd_queue_main;
 
 void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
   (void)nframes;
@@ -42,11 +41,15 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
           } else {
             switch (note) {
             case 60:
-              atomic_store(&cmd_add, 1);
-              break;
+            {
+              command_t cmd = { .type = CMD_ADD_CHANNEL, .channel = -1, .data = 0 };
+              queue_push(&cmd_queue_main, cmd);
+            } break;
             case 61:
-              atomic_store(&cmd_remove, 1);
-              break;
+            {
+              command_t cmd = { .type = CMD_REMOVE_CHANNEL, .channel = -1, .data = 0 };
+              queue_push(&cmd_queue_main, cmd);
+            } break;
             case 62:
             {
               int bch = atomic_load(&bind_channel);
@@ -73,11 +76,15 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
               queue_push(&cmd_queue, cmd);
             } break;
           case 60:
-            atomic_store(&cmd_add, 1);
-            break;
+          {
+            command_t cmd = { .type = CMD_ADD_CHANNEL, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue_main, cmd);
+          } break;
           case 61:
-            atomic_store(&cmd_remove, 1);
-            break;
+          {
+            command_t cmd = { .type = CMD_REMOVE_CHANNEL, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue_main, cmd);
+          } break;
           default:
             break;
           }

src/pipe.c

@@ -13,12 +13,9 @@
 #define FIFO_PATH "/tmp/looper_cmd"
 #define LINE_MAX 256
 
-/* forward‑declare the global queue (defined in looper.c) */
+/* forward‑declare the global queues (defined in looper.c) */
 extern spsc_queue_t cmd_queue;
-
-/* external atomic flags for add/remove (defined in looper.c) */
-extern atomic_int cmd_add;
-extern atomic_int cmd_remove;
+extern spsc_queue_t cmd_queue_main;
 
 static void *pipe_thread_func(void *arg) {
     (void)arg;
@@ -35,9 +32,11 @@ static void *pipe_thread_func(void *arg) {
             line[len-1] = '\0';
 
         if (strcmp(line, "add") == 0) {
-            atomic_store(&cmd_add, 1);
+            command_t cmd = { .type = CMD_ADD_CHANNEL, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue_main, cmd);
         } else if (strcmp(line, "remove") == 0) {
-            atomic_store(&cmd_remove, 1);
+            command_t cmd = { .type = CMD_REMOVE_CHANNEL, .channel = -1, .data = 0 };
+            queue_push(&cmd_queue_main, cmd);
         } else if (strncmp(line, "record ", 7) == 0) {
             int ch = atoi(line + 7);
             command_t cmd = { .type = CMD_CYCLE, .channel = ch, .data = 0 };