Make sure there is only one instance of TrackRecordingService at a time.

MyTracks/src/com/google/android/apps/mytracks/services/PreferenceManager.java

@@ -90,6 +90,12 @@ public class PreferenceManager implements OnSharedPreferenceChangeListener {
   @Override
   public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
       String key) {
+    if (service == null) {
+      Log.w(MyTracksConstants.TAG,
+          "onSharedPreferenceChanged: a preference change (key = " + key
+          + ") after a call to shutdown()");
+      return;
+    }
     if (key == null || key.equals(minRecordingDistanceKey)) {
       service.setMinRecordingDistance(
           sharedPreferences.getInt(
@@ -180,4 +186,10 @@ public class PreferenceManager implements OnSharedPreferenceChangeListener {
         .putLong(recordingTrackKey, id)
         .commit();
   }
+  
+  public void shutdown() {
+    sharedPreferences.unregisterOnSharedPreferenceChangeListener(this);
+    sharedPreferences = null;
+    service = null;
+  }
 }

MyTracks/src/com/google/android/apps/mytracks/services/TrackRecordingService.java

@@ -705,15 +705,22 @@ public class TrackRecordingService extends Service implements LocationListener {
   @Override
   public void onDestroy() {
     Log.d(MyTracksConstants.TAG, "TrackRecordingService.onDestroy");
-    checkLocationListener.cancel();
-    timer.cancel();
+
     isRecording = false;
     showNotification();
+    prefManager.shutdown();
+    prefManager = null;
+    checkLocationListener.cancel();
+    timer.cancel();
+    timer.purge();
     unregisterLocationListener();
     shutdownAnnouncer();
     signalManager.shutdown();
+    signalManager = null;
     splitManager.shutdown();
+    splitManager = null;
     releaseWakeLock();
+    
     super.onDestroy();
   }