SpringBoot项目@Async默认线程池导致OOM问题?

最近看到很一篇文章说SpringBoot项目中@Async默认线程池会导致OOM,因为我的项目中也用到@Async注解，所以赶紧看了一下，在网上搜索@Async导致OOM案例还是很多的，于是我我就研究了一下。

使用SpringBoot 2.0.9.RELEASE 创建演示工程，项目比较简单，使用@EnableAsync开启异步，在TaskService中@Async开启方法异步。

@SpringBootApplication
@EnableAsync
@RestController
public class AsyncDemoApplication {
    @Resource
    private TaskService taskService;
    @GetMapping("/id")
    public String test()  {
        taskService.deel();
        return "ok";
    }
    public static void main(String[] args) {
        SpringApplication.run(AsyncDemoApplication.class, args);
    }
}

@Component
@Slf4j
public class TaskService {

    @Async
    public void deel()  {
        log.info("Thread Name :{} ", Thread.currentThread().getName());
    }
}

从压测结果上来看，刚一开始等待线程数就有3024条，日志中SimpleAsyncTaskExecutor-11922 编号已达到11922个了，看来确实和网上说的一样 @Async默认线程池是SimpleAsyncTaskExecutor,会每次创建一个线程去执行任务，任务量大了会产生OOM。

关键代码：

protected void doExecute(Runnable task) {
   Thread thread = (this.threadFactory != null ? this.threadFactory.newThread(task) : createThread(task));
   thread.start();
}

在SimpleAsyncTaskExecutor的doExecute方法中每次会创建新线程来执行，所以导致瞬间等待线程数达到3024条，确实有点坑人。

升级后结果完全不同了，线程数量并没有上升，线程名也变成task-8 这样的了，看来是SpringBoot 优化掉了这个 SimpleAsyncTaskExecutor

在2.1.0之后的版本多了一个TaskExecutionAutoConfiguration，在项目缺少 Executor Bean的情况下注入了一个ThreadPoolTaskExecutor，作为@Async默认线程池。

@SpringBootApplication
@EnableAsync
@RestController
public class AsyncDemoApplication {

    @Bean("fileTask")
    public Executor fileTask() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(40);
        executor.setQueueCapacity(200);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("file-");
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setAwaitTerminationSeconds(60);
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        return executor;
    }
    @Resource
    private TaskService taskService;

    @GetMapping("/id")
    public String test() {
        taskService.deel();
        return "ok";
    }

    public static void main(String[] args) {
        SpringApplication.run(AsyncDemoApplication.class, args);
    }

从测试结果来看是没有问题，使用项目中配置的fileTask

@SpringBootApplication
@EnableAsync
@RestController
public class AsyncDemoApplication {

    @Bean("fileTask")
    public Executor fileTask() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(40);
        executor.setQueueCapacity(200);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("file-");
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setAwaitTerminationSeconds(60);
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        return executor;
    }

    @Bean("imgTask")
    public Executor imgTask() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(40);
        executor.setQueueCapacity(200);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("img-");
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setAwaitTerminationSeconds(60);
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        return executor;
    }

    @Resource
    private TaskService taskService;

    @GetMapping("/id")
    public String test() {
        taskService.deel();
        return "ok";
    }

    public static void main(String[] args) {
        SpringApplication.run(AsyncDemoApplication.class, args);
    }

如果项目中配置了多个Executor也会使用 SimpleAsyncTaskExecutor

原因是在AsyncExecutionInterceptor 中调用 getDefaultExecutor() 时beanFactory.getBean(TaskExecutor.class) 找到了两个bean所以 报了 NoUniqueBeanDefinitionException，导致没获取到Executor而使用了SimpleAsyncTaskExecutor，所以在fileTask 添加@Primary可解决多个bean问题。

1. SpringBoot 2.1.9 之前版本 使用@Async 不指定 Executor 会使用 SimpleAsyncTaskExecutor，任务量大会导致OOM, SpringBoot 2.1.0之后版本 引入了 TaskExecutionAutoConfiguration使用
   ThreadPoolTaskExecutor作为默认 Executor；
2. 当项目中有多个 Executor 实列时也会使用 SimpleAsyncTaskExecutor，导致OOM，建议@Primary指定主Bean；
3. @Async是可以使用的，最好指定线程池，使用越简单，隐藏问题就越多。