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From GitBox <...@apache.org>
Subject [GitHub] [flink] 1u0 commented on a change in pull request #8523: [FLINK-12481][runtime] Invoke timer callback in task thread (via mailbox)
Date Tue, 28 May 2019 19:50:07 GMT
1u0 commented on a change in pull request #8523: [FLINK-12481][runtime] Invoke timer callback
in task thread (via mailbox)
URL: https://github.com/apache/flink/pull/8523#discussion_r288273753
 
 

 ##########
 File path: flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/SystemProcessingTimeService.java
 ##########
 @@ -253,89 +243,53 @@ int getNumTasksScheduled() {
 	// ------------------------------------------------------------------------
 
 	/**
-	 * Internal task that is invoked by the timer service and triggers the target.
+	 * A context to which {@link ProcessingTimeCallback} would be passed to be invoked when
a timer is up.
 	 */
-	private static final class TriggerTask implements Runnable {
+	public interface ScheduledCallbackExecutionContext {
 
-		private final AtomicInteger serviceStatus;
-		private final Object lock;
-		private final ProcessingTimeCallback target;
-		private final long timestamp;
-		private final AsyncExceptionHandler exceptionHandler;
-
-		private TriggerTask(
-				final AtomicInteger serviceStatus,
-				final AsyncExceptionHandler exceptionHandler,
-				final Object lock,
-				final ProcessingTimeCallback target,
-				final long timestamp) {
-
-			this.serviceStatus = Preconditions.checkNotNull(serviceStatus);
-			this.exceptionHandler = Preconditions.checkNotNull(exceptionHandler);
-			this.lock = Preconditions.checkNotNull(lock);
-			this.target = Preconditions.checkNotNull(target);
-			this.timestamp = timestamp;
-		}
+		void invoke(ProcessingTimeCallback callback, long timestamp) throws InterruptedException;
+	}
 
-		@Override
-		public void run() {
-			synchronized (lock) {
-				try {
-					if (serviceStatus.get() == STATUS_ALIVE) {
-						target.onProcessingTime(timestamp);
-					}
-				} catch (Throwable t) {
-					TimerException asyncException = new TimerException(t);
-					exceptionHandler.handleAsyncException("Caught exception while processing timer.", asyncException);
-				}
-			}
-		}
+	private Runnable wrapOnTimerCallback(ProcessingTimeCallback callback, long timestamp) {
+		return new TimeTrackingDelegate(status, callbackExecutionContext, callback, timestamp,
0);
 	}
 
-	/**
-	 * Internal task which is repeatedly called by the processing time service.
-	 */
-	private static final class RepeatedTriggerTask implements Runnable {
+	private Runnable wrapOnTimerCallback(ProcessingTimeCallback callback, long nextTimestamp,
long period) {
+		return new TimeTrackingDelegate(status, callbackExecutionContext, callback, nextTimestamp,
period);
+	}
 
+	private static final class TimeTrackingDelegate implements Runnable {
 		private final AtomicInteger serviceStatus;
-		private final Object lock;
-		private final ProcessingTimeCallback target;
-		private final long period;
-		private final AsyncExceptionHandler exceptionHandler;
+		private final ScheduledCallbackExecutionContext callbackExecutionContext;
+		private final ProcessingTimeCallback callback;
 
 		private long nextTimestamp;
+		private final long period;
 
-		private RepeatedTriggerTask(
-				final AtomicInteger serviceStatus,
-				final AsyncExceptionHandler exceptionHandler,
-				final Object lock,
-				final ProcessingTimeCallback target,
-				final long nextTimestamp,
-				final long period) {
-
-			this.serviceStatus = Preconditions.checkNotNull(serviceStatus);
-			this.lock = Preconditions.checkNotNull(lock);
-			this.target = Preconditions.checkNotNull(target);
+		TimeTrackingDelegate(
+				AtomicInteger serviceStatus,
+				ScheduledCallbackExecutionContext callbackExecutionContext,
+				ProcessingTimeCallback callback,
+				long timestamp,
+				long period) {
+			this.serviceStatus = serviceStatus;
+			this.callbackExecutionContext = callbackExecutionContext;
+			this.callback = callback;
+			this.nextTimestamp = timestamp;
 			this.period = period;
-			this.exceptionHandler = Preconditions.checkNotNull(exceptionHandler);
-
-			this.nextTimestamp = nextTimestamp;
 		}
 
 		@Override
 		public void run() {
-			synchronized (lock) {
-				try {
-					if (serviceStatus.get() == STATUS_ALIVE) {
-						target.onProcessingTime(nextTimestamp);
-					}
-
-					nextTimestamp += period;
-				} catch (Throwable t) {
-					TimerException asyncException = new TimerException(t);
-					exceptionHandler.handleAsyncException("Caught exception while processing repeated timer
task.", asyncException);
-				}
+			if (serviceStatus.get() != STATUS_ALIVE) {
+				return;
+			}
+			try {
+				callbackExecutionContext.invoke(callback, nextTimestamp);
+			} catch (InterruptedException ex) {
+				Thread.currentThread().interrupt();
 
 Review comment:
   (+ to the other your comment about `InterruptedException`)
   Frankly, I also wonder how and where to handle this exception.
   Same question applies for checkpoints handling in the main task thread (FLINK-12482).
   
   Some of my thoughts:
   
   The root of this exception is in `ReentrantLock.lockInterruptibly()` used in the mailbox.
   If the exception is actually thrown, I interpret it that the mailbox queue is full (the
sender thread had to sleep, assumption that the threads in the time service thread pool don't
have interrupted status set). So if something external interrupts the time service thread
on mailbox, I assume it's somethings "disastrous", like forced shutdown of task manager.
   
   Here, I handle the exception in the `SystemProcessingTimeService`, as the thread belongs
to the thread pool of this service. So the service may decide what to do with such exception.
   
   On the time service side, basically there is not much to do with it and the thread actually
was "told" to be interrupted. So for now, the `Thread.currentThread().interrupt();` action
is the reaction to such situation.

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