junrao commented on a change in pull request #10030: URL: https://github.com/apache/kafka/pull/10030#discussion_r569890466
########## File path: metadata/src/main/java/org/apache/kafka/queue/KafkaEventQueue.java ########## @@ -0,0 +1,420 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.kafka.queue; + +import java.util.HashMap; +import java.util.Map; +import java.util.Objects; +import java.util.TreeMap; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.locks.Condition; +import java.util.concurrent.locks.ReentrantLock; +import java.util.function.Function; +import org.apache.kafka.common.errors.TimeoutException; +import org.apache.kafka.common.utils.KafkaThread; +import org.apache.kafka.common.utils.LogContext; +import org.apache.kafka.common.utils.Time; +import org.slf4j.Logger; + + +public final class KafkaEventQueue implements EventQueue { + /** + * A context object that wraps events. + */ + private static class EventContext { + /** + * The caller-supplied event. + */ + private final Event event; + + /** + * How this event was inserted. + */ + private final EventInsertionType insertionType; + + /** + * The previous pointer of our circular doubly-linked list. + */ + private EventContext prev = this; + + /** + * The next pointer in our circular doubly-linked list. + */ + private EventContext next = this; + + /** + * If this event is in the delay map, this is the key it is there under. + * If it is not in the map, this is null. + */ + private Long deadlineNs = null; + + /** + * The tag associated with this event. + */ + private String tag; + + EventContext(Event event, EventInsertionType insertionType, String tag) { + this.event = event; + this.insertionType = insertionType; + this.tag = tag; + } + + /** + * Insert a new node in the circularly linked list after this node. + */ + void insertAfter(EventContext other) { + this.next.prev = other; + other.next = this.next; + other.prev = this; + this.next = other; + } + + /** + * Insert a new node in the circularly linked list before this node. + */ + void insertBefore(EventContext other) { + this.prev.next = other; + other.prev = this.prev; + other.next = this; + this.prev = other; + } + + /** + * Remove this node from the circularly linked list. + */ + void remove() { + this.prev.next = this.next; + this.next.prev = this.prev; + this.prev = this; + this.next = this; + } + + /** + * Returns true if this node is the only element in its list. + */ + boolean isSingleton() { + return prev == this && next == this; + } + + /** + * Run the event associated with this EventContext. + */ + void run() throws InterruptedException { + try { + event.run(); + } catch (InterruptedException e) { + throw e; + } catch (Exception e) { + event.handleException(e); + } + } + + /** + * Complete the event associated with this EventContext with a timeout exception. + */ + void completeWithTimeout() { + completeWithException(new TimeoutException()); + } + + /** + * Complete the event associated with this EventContext with the specified + * exception. + */ + void completeWithException(Throwable t) { + event.handleException(t); + } + } + + private class EventHandler implements Runnable { + /** + * Event contexts indexed by tag. Events without a tag are not included here. + */ + private final Map<String, EventContext> tagToEventContext = new HashMap<>(); + + /** + * The head of the event queue. + */ + private final EventContext head = new EventContext(null, null, null); + + /** + * An ordered map of times in monotonic nanoseconds to events to time out. + */ + private final TreeMap<Long, EventContext> delayMap = new TreeMap<>(); + + /** + * A condition variable for waking up the event handler thread. + */ + private final Condition cond = lock.newCondition(); + + @Override + public void run() { + try { + handleEvents(); + cleanupEvent.run(); + } catch (Throwable e) { + log.warn("event handler thread exiting with exception", e); + } + } + + private void remove(EventContext eventContext) { + eventContext.remove(); + if (eventContext.deadlineNs != null) { + delayMap.remove(eventContext.deadlineNs); + eventContext.deadlineNs = null; + } + if (eventContext.tag != null) { + tagToEventContext.remove(eventContext.tag, eventContext); + eventContext.tag = null; + } + } + + private void handleEvents() throws InterruptedException { + EventContext toTimeout = null; + EventContext toRun = null; + while (true) { + if (toTimeout != null) { + toTimeout.completeWithTimeout(); + toTimeout = null; + } else if (toRun != null) { + toRun.run(); + toRun = null; + } + lock.lock(); + try { + long awaitNs = Long.MAX_VALUE; + Map.Entry<Long, EventContext> entry = delayMap.firstEntry(); + if (entry != null) { + // Search for timed-out events or deferred events that are ready + // to run. + long now = time.nanoseconds(); + long timeoutNs = entry.getKey(); + EventContext eventContext = entry.getValue(); + if (timeoutNs <= now) { + if (eventContext.insertionType == EventInsertionType.DEFERRED) { + // The deferred event is ready to run. Prepend it to the + // queue. (The value for deferred events is a schedule time + // rather than a timeout.) + remove(eventContext); + head.insertAfter(eventContext); Review comment: > Unless I'm missing something, the event that got prepended to the queue will be immediately run on the next iteration of the loop. There is no opportunity to prepend multiple deferred events to the toRun queue, since only one event can be prepended per loop run, and that event will be immediately run at the top of the loop. Hmm, after the event is prepended, we continue to the next while loop before dequeuing and setting toRun, right? Then, in the next loop, we could be prepending the next deferred item before the previous one runs. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
