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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.eventbus;

import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executor;

/**
 *  An {@link EventBus} that takes the Executor of your choice and uses it to
 *  dispatch events, allowing dispatch to occur asynchronously.
 *
 *  @author Cliff Biffle
 *  @since 10.0
 *
 * @deprecated The Google Guava Core Libraries are deprecated and will not be part of the AEM SDK after April 2023
 */
@Beta
@Deprecated(since = "2022-12-01")
public class AsyncEventBus extends EventBus {

    private final Executor executor;

    /**
     * the queue of events is shared across all threads
     */
    private final ConcurrentLinkedQueue eventsToDispatch = new ConcurrentLinkedQueue();

    /**
     * Creates a new AsyncEventBus that will use {@code executor} to dispatch
     * events.  Assigns {@code identifier} as the bus's name for logging purposes.
     *
     * @param identifier short name for the bus, for logging purposes.
     * @param executor   Executor to use to dispatch events. It is the caller's
     *        responsibility to shut down the executor after the last event has
     *        been posted to this event bus.
     */
    public AsyncEventBus(String identifier, Executor executor) {
        super(identifier);
        this.executor = checkNotNull(executor);
    }

    /**
     * Creates a new AsyncEventBus that will use {@code executor} to dispatch
     * events.
     *
     * @param executor Executor to use to dispatch events. It is the caller's
     *        responsibility to shut down the executor after the last event has
     *        been posted to this event bus.
     */
    public AsyncEventBus(Executor executor) {
        this.executor = checkNotNull(executor);
    }

    @Override
    void enqueueEvent(Object event, EventHandler handler) {
        eventsToDispatch.offer(new EventWithHandler(event, handler));
    }

    /**
     * Dispatch {@code events} in the order they were posted, regardless of
     * the posting thread.
     */
    // only deprecated for external subclasses
    @SuppressWarnings("deprecation")
    @Override
    protected void dispatchQueuedEvents() {
        while (true) {
            EventWithHandler eventWithHandler = eventsToDispatch.poll();
            if (eventWithHandler == null) {
                break;
            }
            dispatch(eventWithHandler.event, eventWithHandler.handler);
        }
    }

    /**
     * Calls the {@link #executor} to dispatch {@code event} to {@code handler}.
     */
    @Override
    void dispatch(final Object event, final EventHandler handler) {
        checkNotNull(event);
        checkNotNull(handler);
        executor.execute(new Runnable() {

            @Override
            public void run() {
                AsyncEventBus.super.dispatch(event, handler);
            }
        });
    }
}