Issue #87: Shutdown AdaptableBus Executor when closing MessagingProvi…

…der to prevent blocked threads after closing the client

Signed-off-by: David Schwilk <david.schwilk@bosch.io>

java/src/main/java/org/eclipse/ditto/client/internal/bus/AdaptableBus.java

@@ -109,6 +109,13 @@ SubscriptionId subscribeForAdaptableWithTimeout(Classification tag,
      */
     boolean unsubscribe(@Nullable SubscriptionId subscriptionId);
 
+    /**
+     * Closes the executor of the adaptable bus .
+     *
+     * @since 1.2.2
+     */
+    void shutdownExecutor();
+
     /**
      * Publish a string message that may or may not be an adaptable.
      *

java/src/main/java/org/eclipse/ditto/client/internal/bus/DefaultAdaptableBus.java

@@ -141,6 +141,12 @@ public void publish(final String message) {
         singleThreadedExecutorService.submit(() -> doPublish(message));
     }
 
+    @Override
+    public void shutdownExecutor() {
+        LOGGER.trace("Shutting down AdaptableBus Executor");
+        singleThreadedExecutorService.shutdownNow();
+    }
+
     // call this in a single-threaded executor so that ordering is preserved
     private void doPublish(final String message) {
         if (publishToOneTimeStringSubscribers(message)) {

java/src/main/java/org/eclipse/ditto/client/messaging/internal/WebSocketMessagingProvider.java

@@ -253,6 +253,7 @@ public void close() {
 
                     cancelScheduledReconnect();
                     authenticationProvider.destroy();
+                    adaptableBus.shutdownExecutor();
                     final WebSocket ws = webSocket.get();
                     if (ws != null) {
                         ws.disconnect();