Add a new exit handler to enable Shairport Sync to exit cleanly — that is, on exit, to clean up everything, e.g. open files, ports, sockets, devices, threads, it has been using.

If cleanup isn’t finished after one second, exit will occur unconditionally.
Use the new exit handler for normal exit, for SIGINT and SIGTERM handling, for abnormal exit after fatal errors, and for handling quit requests from the D-Bus and MPRIS interfaces.

When an unfixable error occurs without an installed unfixable error handler, unlock the mutex protecting Shairport Sync’s alsa backend to permit a clean exit.

Fix a very low-level mutex-locking error that interfered with debugging.

Simplify much mutex lock handling.
Remove lots of old and unused code, variables and definitions.

Update audio_sndio.c to remove some harmless compiler warnings.

Undo adding two seconds for messages to be output before _Exit() on die() to allow messages to be output...
Undo making die() exit unconditionally.

dacp.c

@@ -212,11 +212,7 @@ int dacp_send_command(const char *command, char **body, ssize_t *bodysize) {
       uint64_t start_time = get_absolute_time_in_ns();
       pthread_cleanup_push(addrinfo_cleanup, (void *)&res);
       // only do this one at a time -- not sure it is necessary, but better safe than sorry
-
-      // int mutex_reply = sps_pthread_mutex_timedlock(&dacp_conversation_lock, 2000000, command,
-      // 1);
-      int mutex_reply = debug_mutex_lock(&dacp_conversation_lock, 2000000, 1);
-      // int mutex_reply = pthread_mutex_lock(&dacp_conversation_lock);
+      int mutex_reply = pthread_mutex_lock(&dacp_conversation_lock);
       if (mutex_reply == 0) {
         pthread_cleanup_push(mutex_lock_cleanup, (void *)&dacp_conversation_lock);
 
@@ -390,10 +386,10 @@ void relinquish_dacp_server_information(rtsp_conn_info *conn) {
   // as the conn's connection number
   // this is to signify that the player has stopped, but only if another thread (with a different
   // index) hasn't already taken over the dacp service
-  debug_mutex_lock(&dacp_server_information_lock, 500000, 4);
+  pthread_mutex_lock(&dacp_server_information_lock);
   if (dacp_server.players_connection_thread_index == conn->connection_number)
     dacp_server.players_connection_thread_index = 0;
-  debug_mutex_unlock(&dacp_server_information_lock, 4);
+  pthread_mutex_unlock(&dacp_server_information_lock);
 }
 
 // this will be running on the thread of its caller, not of the conversation thread...
@@ -403,7 +399,7 @@ void relinquish_dacp_server_information(rtsp_conn_info *conn) {
 // Thus, we can keep the DACP port that might have previously been discovered
 void set_dacp_server_information(rtsp_conn_info *conn) {
   // debug(1, "set_dacp_server_information");
-  debug_mutex_lock(&dacp_server_information_lock, 500000, 2);
+  pthread_mutex_lock(&dacp_server_information_lock);
   dacp_server.players_connection_thread_index = conn->connection_number;
 
   if ((conn->dacp_id == NULL) || (strcmp(conn->dacp_id, dacp_server.dacp_id) != 0)) {
@@ -464,11 +460,11 @@ void set_dacp_server_information(rtsp_conn_info *conn) {
 
   debug(3, "set_dacp_server_information set active-remote id to %s.", dacp_server.active_remote_id);
   pthread_cond_signal(&dacp_server_information_cv);
-  debug_mutex_unlock(&dacp_server_information_lock, 3);
+  pthread_mutex_unlock(&dacp_server_information_lock);
 }
 
 void dacp_monitor_port_update_callback(const char *dacp_id, uint16_t port) {
-  debug_mutex_lock(&dacp_server_information_lock, 500000, 2);
+  pthread_mutex_lock(&dacp_server_information_lock);
   debug(3,
         "dacp_monitor_port_update_callback with Remote ID \"%s\", target ID \"%s\" and port "
         "number %d.",
@@ -493,7 +489,7 @@ void dacp_monitor_port_update_callback(const char *dacp_id, uint16_t port) {
     }
   }
   pthread_cond_signal(&dacp_server_information_cv);
-  debug_mutex_unlock(&dacp_server_information_lock, 3);
+  pthread_mutex_unlock(&dacp_server_information_lock);
 }
 
 void *dacp_monitor_thread_code(__attribute__((unused)) void *na) {
@@ -510,7 +506,7 @@ void *dacp_monitor_thread_code(__attribute__((unused)) void *na) {
   while (1) {
     int result = 0;
     int32_t the_volume;
-    pthread_cleanup_debug_mutex_lock(&dacp_server_information_lock, 500000, 4);
+    pthread_mutex_lock_and_cleanup_push(&dacp_server_information_lock);
     if (dacp_server.scan_enable == 0) {
       metadata_hub_modify_prolog();
       int ch = (metadata_store.dacp_server_active != 0) ||