jsancio commented on code in PR #22505:
URL: https://github.com/apache/kafka/pull/22505#discussion_r3375333918
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raft/src/main/java/org/apache/kafka/raft/internals/BlockingMessageQueue.java:
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@@ -17,60 +17,51 @@
package org.apache.kafka.raft.internals;
import org.apache.kafka.common.errors.InterruptException;
-import org.apache.kafka.common.protocol.ApiMessage;
-import org.apache.kafka.raft.RaftMessage;
import org.apache.kafka.raft.RaftMessageQueue;
+import java.util.Optional;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class BlockingMessageQueue implements RaftMessageQueue {
- private static final RaftMessage WAKEUP_MESSAGE = new RaftMessage() {
- @Override
- public int correlationId() {
- return 0;
- }
-
- @Override
- public ApiMessage data() {
- return null;
- }
- };
-
- private final BlockingQueue<RaftMessage> queue = new
LinkedBlockingQueue<>();
- private final AtomicInteger size = new AtomicInteger(0);
+ private final BlockingQueue<QueueEntry> queue = new
LinkedBlockingQueue<>();
+ private final AtomicInteger messageCount = new AtomicInteger(0);
@Override
- public RaftMessage poll(long timeoutMs) {
+ public Optional<QueueEntry> poll(long timeoutMs) {
try {
- RaftMessage message = queue.poll(timeoutMs, TimeUnit.MILLISECONDS);
- if (message == null || message == WAKEUP_MESSAGE) {
- return null;
- } else {
- size.decrementAndGet();
- return message;
+ var entry = queue.poll(timeoutMs, TimeUnit.MILLISECONDS);
+ while (entry != null && entry.message() == null) {
+ // Drain the queue of all of the wakeup events
+ entry = queue.poll();
+ }
Review Comment:
I was originally just fixing the API but decided to change the semantic of
this call for two reasons:
1. The fact that a message is used to implement wake up is an implementation
detail. The user should not be able to observer this. They can observe this
when isEmpty is false yet poll would return null in the old implementation.
2. The old implementation would cause the KRaft state machine
(KafkaRaftClient::pollCurrentState) to get polled once per wake up call even
though there are no new message or the timers have not expired. Conceptually,
multiple wake ups between two calls to poll can be collated into one wake up to
poll.
I am trying to make it more of a level trigger vs an edge trigger.
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