[TIKA-4704] Implement pipes client shutdown in TikaGrpcServerImpl

tika-grpc/src/main/java/org/apache/tika/pipes/grpc/TikaGrpcServer.java

@@ -128,6 +128,9 @@ public void stop() throws InterruptedException {
                     .shutdown()
                     .awaitTermination(30, TimeUnit.SECONDS);
         }
+        if (serviceImpl != null) {
+            serviceImpl.postShutdown();
+        }
     }
 
     /**

tika-grpc/src/main/java/org/apache/tika/pipes/grpc/TikaGrpcServerImpl.java

@@ -483,9 +483,26 @@ public void shutdown() {
             LOG.info("Shutting down embedded Ignite server");
             try {
                 igniteStoreServer.close();
-                igniteStoreServer = null;
             } catch (Exception e) {
                 LOG.error("Error shutting down Ignite server", e);
+            } finally {
+                igniteStoreServer = null;
+            }
+        }
+    }
+
+    /**
+     * Close the pipe client, to be called after TikaGrpcServer has shut down.
+     */
+    void postShutdown() {
+        if (pipesClient != null) {
+            LOG.info("Shutting down the pipes client");
+            try {
+                pipesClient.close();
+            } catch (IOException e) {
+                LOG.error("Error closing the pipes client", e);
+            } finally {
+                pipesClient = null;
             }
         }
     }