kirktrue commented on code in PR #14640:
URL: https://github.com/apache/kafka/pull/14640#discussion_r1423064727
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clients/src/main/java/org/apache/kafka/clients/consumer/internals/AsyncKafkaConsumer.java:
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@@ -1499,6 +1575,149 @@ private void subscribeInternal(Collection<String>
topics, Optional<ConsumerRebal
}
}
+ /**
+ * This method can be used by cases where the caller has an event that
needs to both block for completion but
+ * also process background events. For some events, in order to fully
process the associated logic, the
+ * {@link ConsumerNetworkThread background thread} needs assistance from
the application thread to complete.
+ * If the application thread simply blocked on the event after submitting
it, the processing would deadlock.
+ * The logic herein is basically a loop that performs two tasks in each
iteration:
+ *
+ * <ol>
+ * <li>Process background events, if any</li>
+ * <li><em>Briefly</em> wait for {@link CompletableApplicationEvent an
event} to complete</li>
+ * </ol>
+ *
+ * <p/>
+ *
+ * Each iteration gives the application thread an opportunity to process
background events, which may be
+ * necessary to complete the overall processing.
+ *
+ * <p/>
+ *
+ * As an example, take {@link #unsubscribe()}. To start unsubscribing, the
application thread enqueues an
+ * {@link UnsubscribeApplicationEvent} on the application event queue.
That event will eventually trigger the
+ * rebalancing logic in the background thread. Critically, as part of this
rebalancing work, the
+ * {@link ConsumerRebalanceListener#onPartitionsRevoked(Collection)}
callback needs to be invoked. However,
+ * this callback must be executed on the application thread. To achieve
this, the background thread enqueues a
+ * {@link ConsumerRebalanceListenerCallbackNeededEvent} on its background
event queue. That event queue is
+ * periodically queried by the application thread to see if there's work
to be done. When the application thread
+ * sees {@link ConsumerRebalanceListenerCallbackNeededEvent}, it is
processed, and then a
+ * {@link ConsumerRebalanceListenerCallbackCompletedEvent} is then
enqueued by the application thread on the
+ * background event queue. Moments later, the background thread will see
that event, process it, and continue
+ * execution of the rebalancing logic. The rebalancing logic cannot
complete until the
+ * {@link ConsumerRebalanceListener} callback is performed.
+ *
+ * @param eventProcessor Event processor that contains the queue of events
to process
+ * @param future Event that contains a {@link CompletableFuture};
it is on this future that the
+ * application thread will wait for completion
+ * @param timer Overall timer that bounds how long to wait for
the event to complete
+ * @return {@code true} if the event completed within the timeout, {@code
false} otherwise
+ */
+ // Visible for testing
+ <T> T processBackgroundEvents(EventProcessor<?> eventProcessor,
+ Future<T> future,
+ Timer timer) {
+ log.trace("Will wait up to {} ms for future {} to complete",
timer.remainingMs(), future);
+
+ do {
+ boolean hadEvents = eventProcessor.process();
+
+ try {
+ if (future.isDone()) {
+ // If the event is done (either successfully or
otherwise), go ahead and attempt to return
+ // without waiting. We use the ConsumerUtils.getResult()
method here to handle the conversion
+ // of the exception types.
+ T result = ConsumerUtils.getResult(future);
+ log.trace("Future {} completed successfully", future);
+ return result;
+ } else if (!hadEvents) {
+ // If the above processing yielded no events, then let's
sit tight for a bit to allow the
+ // background thread to either a) finish the task, or b)
populate the background event
+ // queue with things to process in our next loop.
+ Timer pollInterval = time.timer(100L);
+ log.trace("Waiting {} ms for future {} to complete",
pollInterval.remainingMs(), future);
+ T result = ConsumerUtils.getResult(future, pollInterval);
+ log.trace("Future {} completed successfully", future);
+ return result;
+ }
+ } catch (TimeoutException e) {
+ // Ignore this as we will retry the event until the timeout
expires.
+ } finally {
+ timer.update();
+ }
+ } while (timer.notExpired());
+
+ log.trace("Future {} did not complete within timeout", future);
+ throw new TimeoutException("Operation timed out before completion");
+ }
+
+ void updateConsumerGroupMetadata(String newMemberId, int newMemberEpoch) {
Review Comment:
OK. I will revert it and file a separate Jira to refactor the group metadata
updates.
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