JDK 源码分析

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68. DelayQueue

DelayQueue 对元素进行持有直到一个特定的延迟到期。注入其中的元素必须实现 java.util.concurrent.Delayed 接口，该接口定义:

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package java.util.concurrent;

/**
 * A mix-in style interface for marking objects that should be
 * acted upon after a given delay.
 *
 * <p>An implementation of this interface must define a
 * {@code compareTo} method that provides an ordering consistent with
 * its {@code getDelay} method.
 *
 * @since 1.5
 * @author Doug Lea
 */
public interface Delayed extends Comparable<Delayed> {

    /**
     * Returns the remaining delay associated with this object, in the
     * given time unit.
     *
     * @param unit the time unit
     * @return the remaining delay; zero or negative values indicate
     * that the delay has already elapsed
     */
    long getDelay(TimeUnit unit);
}

加入延迟队列的元素都必须实现 Delayed 接口。延迟队列内部是利用 PriorityQueue 实现的，所以还是利用优先队列！Delayed 接口继承了 Comparable。因此优先队列是通过 delay 来排序的。

示例如下：

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package com.diguage.truman.concurrent;

import org.junit.jupiter.api.Test;

import java.util.Objects;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

/**
 * @author D瓜哥, https://www.diguage.com/
 * @since 2020-04-22 16:38
 */
public class DelayQueueTest {
    @Test
    public void test() throws InterruptedException {
        DelayQueue<IntDelay> delayQueue = new DelayQueue<>();
        for (int i = 0; i < 10; i++) {
            delayQueue.add(new IntDelay(i));
        }
        while (!delayQueue.isEmpty()) {
            IntDelay delay = delayQueue.take();
            if (Objects.nonNull(delay)) {
                System.out.println(delay.num);
            }
        }
    }

    public static class IntDelay implements Delayed {

        private int num;
        private long deadline;

        public IntDelay(int num) {
            this.num = num;
            deadline = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(num);
        }

        @Override
        public long getDelay(TimeUnit unit) {
            return deadline - System.currentTimeMillis();
        }

        @Override
        public int compareTo(Delayed o) {
            IntDelay param = (IntDelay) o;
            return Integer.compare(this.num, param.num);
        }
    }

}