mutex protection for auto module vector

prevents crashes during module dup, but not delete

src/jack-audio-module.cc

@@ -87,6 +87,8 @@ void JackAudioModule::wipe_buffers() {
 }
 
 void JackAudioModule::globally_register() {
+	std::unique_lock<std::mutex> lock(g_audio_modules_mutex);
+
 	g_audio_modules.push_back(this);
 
 	/* ensure modules are not filling up their buffers out of sync */
@@ -99,6 +101,8 @@ void JackAudioModule::globally_register() {
 }
 
 void JackAudioModule::globally_unregister() {
+	std::unique_lock<std::mutex> lock(g_audio_modules_mutex);
+
 	/* drop ourselves from active module list */
 	auto x = std::find(g_audio_modules.begin(), g_audio_modules.end(), this);
 	if (x != g_audio_modules.end())

src/skjack.cc

@@ -9,11 +9,14 @@ std::condition_variable g_jack_cv;
 // this would be optimal for correctness, but in practice this gets modified
 // very infrequently and nobody cares if we miss one or two audio frames right
 // after creating or destroying a module...
+std::mutex g_audio_modules_mutex;
 std::vector<JackAudioModule*> g_audio_modules;
 std::atomic<unsigned int> g_audio_blocked(0);
 
 int on_jack_process(jack_nframes_t nframes, void *) {
 	if (!g_jack_client.alive()) return 1;
+	/* audio modules vector is blocked; we have to skip this cycle */
+	if (!g_audio_modules_mutex.try_lock()) return 0;
 
 	for (auto itr = g_audio_modules.begin();
       itr != g_audio_modules.end();
@@ -46,6 +49,8 @@ int on_jack_process(jack_nframes_t nframes, void *) {
 	}
 
 	g_audio_blocked = 0;
+	g_audio_modules_mutex.unlock();
+
 	g_jack_cv.notify_all();
 	return 0;
 }

src/skjack.hh

@@ -27,6 +27,7 @@ extern std::condition_variable g_jack_cv;
 // We'll be using this from here on out.
 extern jaq::client g_jack_client;
 
+extern std::mutex g_audio_modules_mutex;
 extern std::vector<JackAudioModule*> g_audio_modules;
 extern std::atomic<unsigned int> g_audio_blocked;