@EnableAsync @Asnc 以及4种拒绝策略

Posted 2020-10-19 高因咖啡

根据不同的场景,可以选择不同的拒绝策略,如果任务非常重要,线程池队列满了,可以交由调用者线程同步处理.

如果是一些不太重要日志,可以直接丢弃掉.

如果一些可以丢弃,但是又需要知道被丢弃了,可以使用ThreadPoolExecutor.AbortPolicy(),在异常处理中记录日志

/**
 * laizhenwei 2018-1-1 12:46:02
 */
@Configuration
@EnableAsync
public class ExecutorConfig implements AsyncConfigurer {

    /**
     * 替换默认线程池,线程队列满了以后交给调用者执行,也就是同步执行
     * @return
     */
    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(7);
        executor.setMaxPoolSize(42);
        executor.setQueueCapacity(11);
        executor.setThreadNamePrefix("Executor-");
        executor.setAllowCoreThreadTimeOut(false);
        executor.setRejectedExecutionHandler( new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }

    /**
     * 队列满了以后,抛弃任务,但是会抛出 rejectedExecution 如果不处理会中断线程
     * @return
     */
    @Bean
    public Executor myExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(1);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(20);
        executor.setThreadNamePrefix("MyExecutor-");
        executor.setAllowCoreThreadTimeOut(false);
        executor.setRejectedExecutionHandler( new ThreadPoolExecutor.AbortPolicy());
        executor.initialize();
        return executor;
    }

    /**
     * 队列满了,直接丢弃当前任务,不抛出异常
     * @return
     */
    @Bean
    public Executor myExecutor1() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(1);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(20);
        executor.setThreadNamePrefix("MyExecutor1-");
        executor.setAllowCoreThreadTimeOut(false);
        executor.setRejectedExecutionHandler( new ThreadPoolExecutor.DiscardPolicy());
        executor.initialize();
        return executor;
    }

    /**
     * 队列满了,丢弃最老的任务,不抛出异常
     * @return
     */
    @Bean
    public Executor myExecutor2() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(1);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(20);
        executor.setThreadNamePrefix("MyExecutor2-");
        executor.setAllowCoreThreadTimeOut(false);
        executor.setRejectedExecutionHandler( new ThreadPoolExecutor.DiscardOldestPolicy());
        executor.initialize();
        return executor;
    }

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new MyAsyncUncaughtExceptionHandler();
    }

    public static class MyAsyncUncaughtExceptionHandler implements AsyncUncaughtExceptionHandler{
        @Override
        public void handleUncaughtException(Throwable throwable, Method method, Object... objects) {
            System.out.println(throwable.getMessage());
        }
    }

}

调用方式使用 value 是bean 的名称

 @Async("myExecutor")

如果异步处理的方法,涉及到jdbc事务,那么请先理解Spring事务的连接是保存在ThreadLocal中的原理,避免踩坑.