[GitHub] [kafka] dajac commented on a diff in pull request #12590: KAFKA-7109: Close fetch sessions on close of consumer

["dajac (via GitHub)" <gi...@apache.org>]

dajac commented on code in PR #12590:
URL: https://github.com/apache/kafka/pull/12590#discussion_r1100288626


##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/Fetcher.java:
##########
@@ -1933,11 +1943,79 @@ private Map<String, String> topicPartitionTags(TopicPartition tp) {
         }
     }
 
+    // Visible for testing
+    void maybeCloseFetchSessions(final Timer timer) {
+        final Cluster cluster = metadata.fetch();
+        final List<RequestFuture<ClientResponse>> requestFutures = new ArrayList<>();
+        for (final Map.Entry<Integer, FetchSessionHandler> entry : sessionHandlers.entrySet()) {
+            final FetchSessionHandler sessionHandler = entry.getValue();
+            // set the session handler to notify close. This will set the next metadata request to send close message.
+            sessionHandler.notifyClose();
+
+            final int sessionId = sessionHandler.sessionId();
+            final Integer fetchTargetNodeId = entry.getKey();
+            // FetchTargetNode may not be available as it may have disconnected the connection. In such cases, we will
+            // skip sending the close request.
+            final Node fetchTarget = cluster.nodeById(fetchTargetNodeId);
+            if (fetchTarget == null || client.isUnavailable(fetchTarget)) {
+                log.debug("Skip sending close session request to broker {} since it is not reachable", fetchTarget);
+                continue;
+            }
+
+            final RequestFuture<ClientResponse> responseFuture = sendFetchRequestToNode(sessionHandler.newBuilder().build(), fetchTarget);
+            responseFuture.addListener(new RequestFutureListener<ClientResponse>() {
+                @Override
+                public void onSuccess(ClientResponse value) {
+                    log.debug("Successfully sent a close message for fetch session: {} to node: {}", sessionId, fetchTarget);
+                }
+
+                @Override
+                public void onFailure(RuntimeException e) {
+                    log.debug("Unable to a close message for fetch session: {} to node: {}. " +
+                        "This may result in unnecessary fetch sessions at the broker.", sessionId, fetchTarget, e);
+                }
+            });
+
+            requestFutures.add(responseFuture);
+        }
+
+        // Poll to ensure that request has been written to the socket. Wait until either the timer has expired or until
+        // all requests have received a response.
+        do {
+            client.poll(timer, null, true);
+        } while (timer.notExpired() && !requestFutures.stream().allMatch(RequestFuture::isDone));
+
+        if (!requestFutures.stream().allMatch(RequestFuture::isDone)) {
+            // we ran out of time before completing all futures. It is ok since we don't want to block the shutdown
+            // here.
+            log.debug("All requests couldn't be sent in the specific timeout period {}ms. " +
+                "This may result in unnecessary fetch sessions at the broker. Consider increasing the timeout passed for " +
+                "KafkaConsumer.close(Duration timeout)", timer.timeoutMs());
+        }
+    }
+
+    public void close(final Timer timer) {
+        if (!isClosed.compareAndSet(false, true)) {
+            log.info("Fetcher {} is already closed.", this);
+            return;
+        }
+
+        // Shared states (e.g. sessionHandlers) could be accessed by multiple threads (such as heartbeat thread), hence,
+        // it is necessary to acquire a lock on the fetcher instance before modifying the states.

Review Comment:
   Thanks for the clarification. That makes sense.



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