m-trieu commented on code in PR #32774:
URL: https://github.com/apache/beam/pull/32774#discussion_r1824913419


##########
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/AbstractWindmillStream.java:
##########
@@ -154,112 +159,169 @@ private static long debugDuration(long nowMs, long 
startMs) {
 
   /** Reflects that {@link #shutdown()} was explicitly called. */
   protected boolean isShutdown() {
-    return isShutdown.get();
-  }
-
-  private StreamObserver<RequestT> requestObserver() {
-    if (requestObserver == null) {
-      throw new NullPointerException(
-          "requestObserver cannot be null. Missing a call to startStream() to 
initialize.");
-    }
-
-    return requestObserver;
+    return isShutdown;
   }
 
   /** Send a request to the server. */
   protected final void send(RequestT request) {
-    lastSendTimeMs.set(Instant.now().getMillis());
     synchronized (this) {
-      if (streamClosed.get()) {
+      if (isShutdown) {
+        return;
+      }
+
+      if (streamClosed) {
+        // TODO(m-trieu): throw a more specific exception here (i.e 
StreamClosedException)
         throw new IllegalStateException("Send called on a client closed 
stream.");
       }
 
-      requestObserver().onNext(request);
+      try {
+        debugMetrics.recordSend();
+        requestObserver.onNext(request);
+      } catch (StreamObserverCancelledException e) {
+        if (isShutdown) {
+          logger.debug("Stream was shutdown during send.", e);
+          return;
+        }
+
+        requestObserver.onError(e);
+      }
+    }
+  }
+
+  @Override
+  public final void start() {
+    boolean shouldStartStream = false;
+    synchronized (shutdownLock) {
+      if (!isShutdown && !started) {
+        started = true;
+        shouldStartStream = true;
+      }
+    }
+
+    if (shouldStartStream) {
+      startStream();
     }
   }
 
   /** Starts the underlying stream. */
-  protected final void startStream() {
+  private void startStream() {
     // Add the stream to the registry after it has been fully constructed.
     streamRegistry.add(this);
     while (true) {
       try {
         synchronized (this) {
-          startTimeMs.set(Instant.now().getMillis());
-          lastResponseTimeMs.set(0);
-          streamClosed.set(false);
-          // lazily initialize the requestObserver. Gets reset whenever the 
stream is reopened.
-          requestObserver = requestObserverSupplier.get();
+          if (isShutdown) {
+            break;
+          }
+          debugMetrics.recordStart();
+          streamClosed = false;
+          requestObserver.reset();
           onNewStream();
-          if (clientClosed.get()) {
+          if (clientClosed) {
             halfClose();
           }
           return;
         }
+      } catch (WindmillStreamShutdownException e) {
+        logger.debug("Stream was shutdown waiting to start.", e);
       } catch (Exception e) {
-        LOG.error("Failed to create new stream, retrying: ", e);
+        logger.error("Failed to create new stream, retrying: ", e);
         try {
           long sleep = backoff.nextBackOffMillis();
-          sleepUntil.set(Instant.now().getMillis() + sleep);
-          Thread.sleep(sleep);
-        } catch (InterruptedException | IOException i) {
+          debugMetrics.recordSleep(sleep);
+          sleeper.sleep(sleep);
+        } catch (InterruptedException ie) {
+          Thread.currentThread().interrupt();
+          logger.info(
+              "Interrupted during {} creation backoff. The stream will not be 
created.",
+              getClass());
+          break;
+        } catch (IOException ioe) {
           // Keep trying to create the stream.
         }
       }
     }
+
+    // We were never able to start the stream, remove it from the stream 
registry. Otherwise, it is
+    // removed when closed.
+    streamRegistry.remove(this);
   }
 
-  protected final Executor executor() {
-    return executor;
+  /**
+   * Execute the runnable using the {@link #executor} handling the executor 
being in a shutdown
+   * state.
+   */
+  protected final void executeSafely(Runnable runnable) {
+    try {
+      executor.execute(runnable);
+    } catch (RejectedExecutionException e) {
+      logger.debug("{}-{} has been shutdown.", getClass(), backendWorkerToken);
+    }
   }
 
-  public final synchronized void maybeSendHealthCheck(Instant 
lastSendThreshold) {
-    if (lastSendTimeMs.get() < lastSendThreshold.getMillis() && 
!clientClosed.get()) {
+  public final void maybeSendHealthCheck(Instant lastSendThreshold) {
+    if (!clientClosed && debugMetrics.lastSendTimeMs() < 
lastSendThreshold.getMillis()) {
       try {
         sendHealthCheck();
       } catch (RuntimeException e) {
-        LOG.debug("Received exception sending health check.", e);
+        logger.debug("Received exception sending health check.", e);
       }
     }
   }
 
   protected abstract void sendHealthCheck();
 
-  // Care is taken that synchronization on this is unnecessary for all status 
page information.
-  // Blocking sends are made beneath this stream object's lock which could 
block status page
-  // rendering.
+  /**
+   * @implNote Care is taken that synchronization on this is unnecessary for 
all status page
+   *     information. Blocking sends are made beneath this stream object's 
lock which could block
+   *     status page rendering.
+   */
+  @SuppressWarnings("GuardedBy")

Review Comment:
   it means we will need to acquire "this" lock here



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