m-trieu commented on code in PR #34053:
URL: https://github.com/apache/beam/pull/34053#discussion_r2015091265


##########
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/GrpcDispatcherClient.java:
##########
@@ -132,25 +132,23 @@ ImmutableSet<HostAndPort> getDispatcherEndpoints() {
 
   /** Will block the calling thread until the initial endpoints are present. */
   public CloudWindmillMetadataServiceV1Alpha1Stub 
getWindmillMetadataServiceStubBlocking() {
-    boolean initialized = false;
     long secondsWaited = 0;
-    while (!initialized) {
-      LOG.info(
-          "Blocking until Windmill Service endpoint has been set. "
-              + "Currently waited for [{}] seconds.",
-          secondsWaited);
-      try {
-        initialized = onInitializedEndpoints.await(10, TimeUnit.SECONDS);
+    try {
+      while (!onInitializedEndpoints.await(10, TimeUnit.SECONDS)) {
         secondsWaited += 10;
-      } catch (InterruptedException e) {
-        LOG.error(
-            "Interrupted while waiting for initial Windmill Service endpoints. 
"
-                + "These endpoints are required to do any pipeline 
processing.",
-            e);
+        LOG.debug(
+            "Blocking until Windmill Service endpoint has been set. "
+                + "Currently waited for [{}] seconds.",
+            secondsWaited);
       }
+    } catch (InterruptedException e) {
+      LOG.error(
+          "Interrupted while waiting for initial Windmill Service endpoints. "
+              + "These endpoints are required to do any pipeline processing.",
+          e);

Review Comment:
   done



##########
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/streaming/harness/BackendWorkerMetadataVendor.java:
##########
@@ -0,0 +1,179 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.beam.runners.dataflow.worker.streaming.harness;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
+import javax.annotation.concurrent.ThreadSafe;
+import 
org.apache.beam.runners.dataflow.worker.windmill.Windmill.WorkerMetadataResponse;
+import org.apache.beam.runners.dataflow.worker.windmill.WindmillEndpoints;
+import 
org.apache.beam.runners.dataflow.worker.windmill.client.WindmillStream.GetWorkerMetadataStream;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.MoreExecutors;
+import 
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Manages vending the backend worker metadata to a single consumer.
+ *
+ * <p>Internally restarts the underlying {@link GetWorkerMetadataStream} to 
gracefully close the
+ * stream and prevent gRPC {@link
+ * org.apache.beam.vendor.grpc.v1p69p0.io.grpc.Status#DEADLINE_EXCEEDED} 
statuses.
+ */
+@ThreadSafe
+final class BackendWorkerMetadataVendor {
+  private static final Logger LOG = 
LoggerFactory.getLogger(BackendWorkerMetadataVendor.class);
+  private static final int GET_WORKER_METADATA_STREAM_TIMEOUT_MINUTES = 3;
+  private static final String BACKEND_WORKER_METADATA_VENDOR_THREAD_NAME =
+      "BackendWorkerMetadataVendorThread";
+  private static final WorkerMetadataResponse NO_WORKER_METADATA =
+      WorkerMetadataResponse.getDefaultInstance();
+
+  private final WorkerMetadataStreamFactory getWorkerMetadataStreamFactory;
+  private final ExecutorService workerMetadataFetcher;
+  private final AtomicBoolean isRunning = new AtomicBoolean(false);
+
+  private BackendWorkerMetadataVendor(
+      WorkerMetadataStreamFactory getWorkerMetadataStreamFactory,
+      ExecutorService workerMetadataFetcher) {
+    this.getWorkerMetadataStreamFactory = getWorkerMetadataStreamFactory;
+    this.workerMetadataFetcher = workerMetadataFetcher;
+  }
+
+  static BackendWorkerMetadataVendor create(
+      WorkerMetadataStreamFactory getWorkerMetadataStreamFactory) {
+    return new BackendWorkerMetadataVendor(
+        getWorkerMetadataStreamFactory,
+        Executors.newSingleThreadExecutor(
+            new ThreadFactoryBuilder()
+                .setNameFormat(BACKEND_WORKER_METADATA_VENDOR_THREAD_NAME)
+                .build()));
+  }
+
+  /**
+   * Starts the vending of backend worker metadata, passing it to 
endpointsConsumer for processing.
+   * Returns a {@link CompletableFuture} that can be used to block until the 
initial {@link
+   * GetWorkerMetadataStream} has been started.
+   */
+  CompletableFuture<Void> start(Consumer<WindmillEndpoints> endpointsConsumer) 
{
+    if (isRunning.compareAndSet(false, true)) {
+      LOG.debug("Starting WorkerMetadataVendor...");
+
+      CountDownLatch initialStreamStarted = new CountDownLatch(1);
+
+      workerMetadataFetcher.execute(
+          () -> {
+            boolean isInitialWorkerMetadata = true;
+            WorkerMetadataResponse initialWorkerMetadata = NO_WORKER_METADATA;
+
+            while (isRunning.get()) {
+              GetWorkerMetadataStream getWorkerMetadataStream =
+                  getWorkerMetadataStreamFactory.create(initialWorkerMetadata, 
endpointsConsumer);
+              LOG.debug(
+                  "Starting GetWorkerMetadataStream w/ metadata version {}.",
+                  initialWorkerMetadata.getMetadataVersion());
+              getWorkerMetadataStream.start();
+
+              if (isInitialWorkerMetadata) {
+                isInitialWorkerMetadata = false;
+                initialStreamStarted.countDown();
+              }
+
+              // Await stream termination and propagate the most current 
worker metadata to start
+              // the next stream.
+              initialWorkerMetadata = 
awaitGracefulTermination(getWorkerMetadataStream);
+              LOG.debug(
+                  "Current GetWorkerMetadataStream terminated. Propagating 
metadata version {} to the next stream.",
+                  initialWorkerMetadata.getMetadataVersion());
+            }
+          });
+
+      return CompletableFuture.runAsync(
+          () -> {
+            int secondsWaited = 0;
+            try {
+              while (!initialStreamStarted.await(10, TimeUnit.SECONDS) && 
isRunning.get()) {
+                secondsWaited += 10;
+                LOG.debug(
+                    "Waited {} seconds for initial GetWorkerMetadataStream to 
start.",
+                    secondsWaited);
+              }
+            } catch (InterruptedException e) {
+              LOG.debug("Interrupted waiting for initial 
GetWorkerMetadataStream to start.");
+              Thread.currentThread().interrupt();
+            }
+          },
+          // Run this on the calling thread.
+          MoreExecutors.directExecutor());
+    }
+
+    return CompletableFuture.completedFuture(null);
+  }
+
+  void stop() {
+    if (isRunning.compareAndSet(true, false)) {
+      LOG.debug("Shutting down WorkerMetadataVendor...");
+      workerMetadataFetcher.shutdownNow();
+      boolean isShutdown = false;
+      try {
+        isShutdown =
+            workerMetadataFetcher.awaitTermination(
+                GET_WORKER_METADATA_STREAM_TIMEOUT_MINUTES, TimeUnit.MINUTES);
+      } catch (InterruptedException e) {
+        Thread.currentThread().interrupt();
+      }
+
+      if (!isShutdown) {
+        LOG.warn("Unable to shutdown WorkerMetadataFetcher.");
+      }
+    }
+  }
+
+  /**
+   * Terminate the stream after {@code 
GET_WORKER_METADATA_STREAM_TIMEOUT_MINUTES}, and return the
+   * current WorkerMetadata at the time of termination used to start the next 
{@link
+   * GetWorkerMetadataStream}.
+   */
+  private WorkerMetadataResponse awaitGracefulTermination(
+      GetWorkerMetadataStream getWorkerMetadataStream) {
+    try {
+      // Reconnect every now and again to avoid hitting gRPC deadlines. If at 
any point the server
+      // closes the stream, we will reconnect immediately; otherwise shutdown 
the stream after some
+      // time and create a new one.
+      if (!getWorkerMetadataStream.awaitTermination(
+          GET_WORKER_METADATA_STREAM_TIMEOUT_MINUTES, TimeUnit.MINUTES)) {
+        getWorkerMetadataStream.halfClose();
+      }
+
+      // If halfClose() didn't gracefully close the stream, forcefully 
shutdown().
+      if (!getWorkerMetadataStream.awaitTermination(30, TimeUnit.SECONDS)) {
+        getWorkerMetadataStream.shutdown();
+      }
+
+    } catch (InterruptedException e) {
+      LOG.debug("WorkerMetadataVendor interrupted unexpectedly.");

Review Comment:
   done



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