event_pipe: added pipe_event enum and callbacks

Make the event_pipe (formerly main_notify) send/receive a set of
events, with a callback for each one.

The default event PIPE_EVENT_SIGNAL does not have a callback.  It
is still there for waking up the main thread, when it is waiting for
the player thread.

src/event_pipe.c

@@ -28,14 +28,45 @@
 
 GThread *main_task;
 static int event_pipe[2];
+static GMutex *event_pipe_mutex;
+static bool pipe_events[PIPE_EVENT_MAX];
+static event_pipe_callback_t event_pipe_callbacks[PIPE_EVENT_MAX];
 
-static void consume_pipe(void)
+/**
+ * Invoke the callback for a certain event.
+ */
+static void
+event_pipe_invoke(enum pipe_event event)
+{
+	assert((unsigned)event < PIPE_EVENT_MAX);
+	assert(event != PIPE_EVENT_SIGNAL);
+	assert(event_pipe_callbacks[event] != NULL);
+
+	event_pipe_callbacks[event]();
+}
+
+static bool consume_pipe(void)
 {
 	char buffer[256];
 	ssize_t r = read(event_pipe[0], buffer, sizeof(buffer));
+	bool events[PIPE_EVENT_MAX];
 
 	if (r < 0 && errno != EAGAIN && errno != EINTR)
 		FATAL("error reading from pipe: %s\n", strerror(errno));
+
+	g_mutex_lock(event_pipe_mutex);
+	memcpy(events, pipe_events, sizeof(events));
+	memset(pipe_events, 0, sizeof(pipe_events));
+	g_mutex_unlock(event_pipe_mutex);
+
+	for (unsigned i = 0; i < PIPE_EVENT_MAX; ++i)
+		if (i != PIPE_EVENT_SIGNAL && events[i])
+			/* invoke the event handler; the SIGNAL event
+			   has no handler, because it is handled by
+			   the event_pipe_wait() caller */
+			event_pipe_invoke(i);
+
+	return events[PIPE_EVENT_SIGNAL];
 }
 
 static gboolean
@@ -44,7 +75,6 @@ main_notify_event(G_GNUC_UNUSED GIOChannel *source,
 		  G_GNUC_UNUSED gpointer data)
 {
 	consume_pipe();
-	main_notify_triggered();
 	return true;
 }
 
@@ -63,22 +93,55 @@ void event_pipe_init(void)
 	g_io_add_watch(channel, G_IO_IN, main_notify_event, NULL);
 	g_io_channel_unref(channel);
 
+	event_pipe_mutex = g_mutex_new();
+
 	main_task = g_thread_self();
 }
 
 void event_pipe_deinit(void)
 {
+	g_mutex_free(event_pipe_mutex);
+
 	xclose(event_pipe[0]);
 	xclose(event_pipe[1]);
 }
 
-void event_pipe_signal(void)
+void
+event_pipe_register(enum pipe_event event, event_pipe_callback_t callback)
 {
-	ssize_t w = write(event_pipe[1], "", 1);
+	assert(event != PIPE_EVENT_SIGNAL);
+	assert((unsigned)event < PIPE_EVENT_MAX);
+	assert(event_pipe_callbacks[event] == NULL);
+
+	event_pipe_callbacks[event] = callback;
+}
+
+void event_pipe_emit(enum pipe_event event)
+{
+	ssize_t w;
+
+	assert((unsigned)event < PIPE_EVENT_MAX);
+
+	g_mutex_lock(event_pipe_mutex);
+	if (pipe_events[event]) {
+		/* already set: don't write */
+		g_mutex_unlock(event_pipe_mutex);
+		return;
+	}
+
+	pipe_events[event] = true;
+	g_mutex_unlock(event_pipe_mutex);
+
+	w = write(event_pipe[1], "", 1);
 	if (w < 0 && errno != EAGAIN && errno != EINTR)
 		g_error("error writing to pipe: %s", strerror(errno));
 }
 
+void event_pipe_signal(void)
+{
+	event_pipe_emit(PIPE_EVENT_SIGNAL);
+}
+
 void event_pipe_wait(void)
 {
 	consume_pipe();