kirktrue commented on code in PR #16686:
URL: https://github.com/apache/kafka/pull/16686#discussion_r1752972613
##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AsyncKafkaConsumer.java:
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@@ -1302,6 +1304,42 @@ private void releaseAssignmentAndLeaveGroup(final Timer
timer) {
}
}
+ /**
+ * The unsubscribe process requires a handful of back-and-forth trips
between the application thread and
+ * the background thread:
+ *
+ * <ol>
+ * <li>
+ * Application thread: enqueue {@link UnsubscribeEvent}
+ * </li>
+ * <li>
+ * Background thread: process {@link UnsubscribeEvent} and
+ * enqueue {@link
ConsumerRebalanceListenerCallbackNeededEvent}
+ * </li>
+ * <li>
+ * Application thread: process {@link
ConsumerRebalanceListenerCallbackNeededEvent},
+ * invoke appropriate {@link
ConsumerRebalanceListener} method, and
+ * enqueue {@link
ConsumerRebalanceListenerCallbackCompletedEvent}
+ * </li>
+ * <li>
+ * Background thread: process {@link
ConsumerRebalanceListenerCallbackCompletedEvent} and
+ * enqueue {@link
NetworkClientDelegate.UnsentRequest} to send the
+ * {@link ConsumerGroupHeartbeatRequest} to
leave the consumer group
+ * </li>
+ * </ol>
+ *
+ * In cases where the incoming {@link Timer timer} has very little
remaining time, e.g. 0, it is impossible
+ * to perform the thread switches necessary to leave the group. Therefore,
in cases where there isn't much
+ * of a timeout left, increase it slightly (presently 1000 ms.) to improve
the chances for the consumer to
+ * properly leave the group.
Review Comment:
I've submitted two new Jiras:
1. KAFKA-17518: AsyncKafkaConsumer cannot reliably leave group when closed
with small timeout
2. KAFKA-17519: Define and validate correctness of Consumer.close() and its
timeout when thread is interrupted
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