ThreadPoolTaskExecutor 异步配置

使用默认的 ThreadPoolExecutor.DiscardPolicy， 直接丢弃当前超出队列的数据。

使用自定义的处理器，该处理器会阻塞地向BlockQueen 放数据，直到有剩余空间可用（注意这可能导致很多线程处于 executor.getQueue().put(r) 方法线程等待中）。

/**
 * default executor is SimpleAsyncTaskExecutor
 * 配置参考 https://docs.spring.io/spring-boot/docs/2.3.0.RELEASE/reference/html/spring-boot-features.html#boot-features-task-execution-scheduling
 */
@Slf4j
@Configuration
@EnableAsync
public class AsyncConf {

    @Primary
    @Bean(name = "threadPoolTaskExecutor")
    public Executor threadPoolTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(4);
        executor.setMaxPoolSize(4);
        executor.setQueueCapacity(6000);
        executor.setKeepAliveSeconds(10);
        executor.setThreadNamePrefix("My Async Thread-");

        executor.setRejectedExecutionHandler(new RejectedExecutionHandlerImpl());
        executor.initialize();
        return executor;
    }

    public static class RejectedExecutionHandlerImpl implements RejectedExecutionHandler {

        @Override
        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
            try {
                //阻塞当前线程
                executor.getQueue().put(r);
            } catch (InterruptedException e) {
                throw new RejectedExecutionException("There was an unexpected InterruptedException whilst waiting to add a Runnable in the executor's blocking queue", e);
            }
        }
    }
}