lianetm commented on code in PR #15640:
URL: https://github.com/apache/kafka/pull/15640#discussion_r1585466853
##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/events/CompletableEvent.java:
##########
@@ -16,9 +16,118 @@
*/
package org.apache.kafka.clients.consumer.internals.events;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+
+import java.time.Duration;
+import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeoutException;
+
+import static java.util.Objects.requireNonNull;
+/**
+ * {@code CompletableEvent} is an interface that is used by both {@link
CompletableApplicationEvent} and
+ * {@link CompletableBackgroundEvent} for common processing and logic. A
{@code CompletableEvent} is one that
+ * allows the caller to get the {@link #future() future} related to the event
and the event's
+ * {@link #deadlineMs() expiration timestamp}.
+ *
+ * @param <T> Return type for the event when completed
+ */
public interface CompletableEvent<T> {
+ /**
+ * Returns the {@link CompletableFuture future} associated with this
event. Any event will have some related
+ * logic that is executed on its behalf. The event can complete in one of
the following ways:
+ *
+ * <ul>
+ * <li>
+ * Success: when the logic for the event completes successfully,
the data generated by that event
+ * (if applicable) is passed to {@link
CompletableFuture#complete(Object)}. In the case where the generic
+ * bound type is specified as {@link Void}, {@code null} is
provided.</li>
+ * <li>
+ * Error: when the the event logic generates an error, the error
is passed to
+ * {@link CompletableFuture#completeExceptionally(Throwable)}.
+ * </li>
+ * <li>
+ * Timeout: when the time spent executing the event logic exceeds
the {@link #deadlineMs() deadline}, an
+ * instance of {@link TimeoutException} should be created and
passed to
+ * {@link CompletableFuture#completeExceptionally(Throwable)}.
+ * </li>
+ * <li>
+ * Cancelled: when an event remains incomplete when the consumer
closes, the future will be
+ * {@link CompletableFuture#cancel(boolean) cancelled}. Attempts
to {@link Future#get() get the result}
Review Comment:
The reaper actually calls `completeExceptionally` with a
`CancellationException` instead of calling `CompletableFuture#cancel(boolean)`.
Unless I'm missing a subtle semantic diff they should achieve the same, but
still, adding a link to `cancel` here would not be accurate I would say.
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