Fix race condition when stopDiscovery() is called during onServiceFound()/onServiceLost()

app/src/main/java/com/limelight/nvstream/mdns/NsdManagerDiscoveryAgent.java

@@ -20,13 +20,13 @@ import java.util.concurrent.TimeUnit;
 @TargetApi(Build.VERSION_CODES.UPSIDE_DOWN_CAKE)
 public class NsdManagerDiscoveryAgent extends MdnsDiscoveryAgent {
     private static final String SERVICE_TYPE = "_nvstream._tcp";
-    private NsdManager nsdManager;
+    private final NsdManager nsdManager;
     private boolean discoveryActive;
     private boolean wantsDiscoveryActive;
     private final HashMap<String, NsdManager.ServiceInfoCallback> serviceCallbacks = new HashMap<>();
     private final ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 1, 0, TimeUnit.SECONDS, new LinkedBlockingQueue<>());
 
-    private NsdManager.DiscoveryListener discoveryListener = new NsdManager.DiscoveryListener() {
+    private final NsdManager.DiscoveryListener discoveryListener = new NsdManager.DiscoveryListener() {
         @Override
         public void onStartDiscoveryFailed(String serviceType, int errorCode) {
             discoveryActive = false;
@@ -63,6 +63,13 @@ public class NsdManagerDiscoveryAgent extends MdnsDiscoveryAgent {
 
         @Override
         public void onServiceFound(NsdServiceInfo nsdServiceInfo) {
+            // Protect against racing stopDiscovery() call
+            synchronized (serviceCallbacks) {
+                // Bail if we've been stopped
+                if (!wantsDiscoveryActive) {
+                    return;
+                }
+
                 LimeLog.info("NSD: Machine appeared: "+nsdServiceInfo.getServiceName());
 
                 NsdManager.ServiceInfoCallback serviceInfoCallback = new NsdManager.ServiceInfoCallback() {
@@ -90,16 +97,25 @@ public class NsdManagerDiscoveryAgent extends MdnsDiscoveryAgent {
                 nsdManager.registerServiceInfoCallback(nsdServiceInfo, executor, serviceInfoCallback);
                 serviceCallbacks.put(nsdServiceInfo.getServiceName(), serviceInfoCallback);
             }
+        }
 
         @Override
         public void onServiceLost(NsdServiceInfo nsdServiceInfo) {
-            LimeLog.info("NSD: Machine lost: "+nsdServiceInfo.getServiceName());
+            // Protect against racing stopDiscovery() call
+            synchronized (serviceCallbacks) {
+                // Bail if we've been stopped
+                if (!wantsDiscoveryActive) {
+                    return;
+                }
+
+                LimeLog.info("NSD: Machine lost: " + nsdServiceInfo.getServiceName());
 
                 NsdManager.ServiceInfoCallback serviceInfoCallback = serviceCallbacks.remove(nsdServiceInfo.getServiceName());
                 if (serviceInfoCallback != null) {
                     nsdManager.unregisterServiceInfoCallback(serviceInfoCallback);
                 }
             }
+        }
     };
 
     public NsdManagerDiscoveryAgent(Context context, MdnsDiscoveryListener listener) {
@@ -119,6 +135,8 @@ public class NsdManagerDiscoveryAgent extends MdnsDiscoveryAgent {
 
     @Override
     public void stopDiscovery() {
+        // Protect against racing ServiceInfoCallback and DiscoveryListener callbacks
+        synchronized (serviceCallbacks) {
             wantsDiscoveryActive = false;
 
             // Unregister the service discovery listener
@@ -132,6 +150,7 @@ public class NsdManagerDiscoveryAgent extends MdnsDiscoveryAgent {
             }
             serviceCallbacks.clear();
         }
+    }
 
     private static Inet4Address[] getV4Addrs(List<InetAddress> addrs) {
         int matchCount = 0;