Examples: Updated HelloWorldServer to use Executor (#11850)

Author: NaveenPrasannaV

examples/src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java

@@ -23,6 +23,8 @@
 import java.io.IOException;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 /**
  * Server that manages startup/shutdown of a {@code Greeter} server.
@@ -31,11 +33,20 @@ public class HelloWorldServer {
  private static final Logger logger = Logger.getLogger(HelloWorldServer.class.getName());
 
  private Server server;
-
  private void start() throws IOException {
  /* The port on which the server should run */
  int port = 50051;
+ /*
+ * By default gRPC uses a global, shared Executor.newCachedThreadPool() for gRPC callbacks into
+ * your application. This is convenient, but can cause an excessive number of threads to be
+ * created if there are many RPCs. It is often better to limit the number of threads your
+ * application uses for processing and let RPCs queue when the CPU is saturated.
+ * The appropriate number of threads varies heavily between applications.
+ * Async application code generally does not need more threads than CPU cores.
+ */
+ ExecutorService executor = Executors.newFixedThreadPool(2);
  server = Grpc.newServerBuilderForPort(port, InsecureServerCredentials.create())
+ .executor(executor)
  .addService(new GreeterImpl())
  .build()
  .start();
@@ -48,7 +59,12 @@ public void run() {
  try {
  HelloWorldServer.this.stop();
  } catch (InterruptedException e) {
+ if (server != null) {
+ server.shutdownNow();
+ }
  e.printStackTrace(System.err);
+ } finally {
+ executor.shutdown();
  }
  System.err.println("*** server shut down");
  }