前言

四种线程池拒绝策略

线程池默认的拒绝策略

/**
 * The default rejected execution handler
 */
private static final RejectedExecutionHandler defaultHandler =
    new AbortPolicy();

public class ThreadPoolTest {

    public static void main(String[] args) {

        BlockingQueue<Runnable> queue = new ArrayBlockingQueue<>(100);
        ThreadFactory factory = r -> new Thread(r, "test-thread-pool");
        ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 5,
                0L, TimeUnit.SECONDS, queue, factory);
        while (true) {
            executor.submit(() -> {
                try {
                    System.out.println(queue.size());
                    Thread.sleep(10000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
    }

}

设置线程池拒绝策略

@Configuration
public class TaskExecutorConfig implements AsyncConfigurer {
    /**
     * Set the ThreadPoolExecutor's core pool size.
     */
    private static final int CORE_POOL_SIZE = 5;
    /**
     * Set the ThreadPoolExecutor's maximum pool size.
     */
    private static final int MAX_POOL_SIZE = 5;
    /**
     * Set the capacity for the ThreadPoolExecutor's BlockingQueue.
     */
    private static final int QUEUE_CAPACITY = 1000;

    /**
     * 通过重写getAsyncExecutor方法，制定默认的任务执行由该方法产生
     * <p>
     * 配置类实现AsyncConfigurer接口并重写getAsyncExcutor方法，并返回一个ThreadPoolTaskExevutor
     * 这样我们就获得了一个基于线程池的TaskExecutor
     */
    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
        taskExecutor.setCorePoolSize(CORE_POOL_SIZE);
        taskExecutor.setMaxPoolSize(MAX_POOL_SIZE);
        taskExecutor.setQueueCapacity(QUEUE_CAPACITY);
        taskExecutor.initialize();
        taskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
        return taskExecutor;
    }
}

拒绝策略场景分析

AbortPolicy

DiscardPolicy

DiscardOldestPolicy

CallerRunsPolicy

public static void main(String[] args) {

    BlockingQueue<Runnable> queue = new ArrayBlockingQueue<>(10);
    ThreadFactory factory = r -> new Thread(r, "test-thread-pool");
    ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 5,
                                                         0L, TimeUnit.SECONDS, queue, factory, new ThreadPoolExecutor.CallerRunsPolicy());
    for (int i = 0; i < 1000; i  ) {
        executor.submit(() -> {
            try {
                System.out.println(Thread.currentThread().getName()   ":执行任务");
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
    }
}

总结