"线程池中线程异常后:销毁还是复用?"

云上有数芯 2024-03-29 09:24:33
一、一个线程池中的线程异常了,那么线程池会怎么处理这个线程?

需要说明,本文的线程池都是java.util.concurrent.ExecutorService线程池,本文将围绕验证,阅读源码俩方面来解析这个问题。

二、代码验证2.1 验证execute提交线程池中2.1.1 测试代码: public ThreadPoolExecutorDeadTest { public static void main(String[] args) throws InterruptedException { ExecutorService executorService = buildThreadPoolExecutor(); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute-exception")); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); Thread.sleep(5000); System.out.println("再次执行任务======================="); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); executorService.execute(() -> exeTask("execute")); } public static ExecutorService buildThreadPoolExecutor() { return new ThreadPoolExecutor(5, 10, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1000), new ThreadFactoryBuilder().setNameFormat("test-%s").build() , new ThreadPoolExecutor.CallerRunsPolicy()); } private static void exeTask(String name) { String printStr = "[thread-name:" + Thread.currentThread().getName() + ",执行方式:" + name + "]"; if ("execute-exception".equals(name)) { throw new RuntimeException(printStr + ", 我抛异常了"); } else { System.out.println(printStr); } }}2.1.2 执行结果如下:

2.1.3 结论:execute 提交到线程池的方式,如果执行中抛出异常,并且没有在执行逻辑中catch,那么会抛出异常,并且移除抛出异常的线程,创建新的线程放入到线程池中。2.2 验证submit提交线程池中2.2.1 测试代码:public ThreadPoolExecutorDeadTest { public static void main(String[] args) throws InterruptedException { ExecutorService executorService = buildThreadPoolExecutor(); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute-exception")); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); Thread.sleep(5000); System.out.println("再次执行任务======================="); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); executorService.submit(() -> exeTask("execute")); } public static ExecutorService buildThreadPoolExecutor() { return new ThreadPoolExecutor(5, 10, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<>(1000), new ThreadFactoryBuilder().setNameFormat("test-%s").build() , new ThreadPoolExecutor.CallerRunsPolicy()); } private static void exeTask(String name) { String printStr = "[thread-name:" + Thread.currentThread().getName() + ",执行方式:" + name + "]"; if ("execute-exception".equals(name)) { throw new RuntimeException(printStr + ", 我抛异常了"); } else { System.out.println(printStr); } }}2.2.2 执行结果如下:

2.2.3 结论:

submit 提交到线程池的方式,如果执行中抛出异常,并且没有catch,不会抛出异常,不会创建新的线程。

三、源码解析3.1 java.util.concurrent.AbstractExecutorService#submit(java.lang.Runnable)

3.2 查看execute方法的执行逻辑java.util.concurrent.ThreadPoolExecutor#runWorker

3.3 java.util.concurrent.ThreadPoolExecutor#processWorkerExit

可以发现,如果抛出异常,会移除抛出异常的线程,创建新的线程。3.4 为什么submit方法,没有创建新的线程,而是继续复用原线程?

还记得,我们在3.1的时候,发现submit也是调用了execute方法,但是在调用之前,包装了一层 RunnableFuture,那一定是在RunnableFuture的实现 FutureTask中有特殊处理了,我们查看源码可以发现。

但是,我们通过java.util.concurrent.FutureTask#get(),就可以获取对应的异常信息。

四、总结当一个线程池里面的线程异常后:

◦当执行方式是execute时,可以看到堆栈异常的输出,线程池会把这个线程移除掉,并创建一个新的线程放到线程池中。

◦当执行方式是submit时,堆栈异常没有输出。但是调用Future.get()方法时,可以捕获到异常,不会把这个线程移除掉,也不会创建新的线程放入到线程池中。

以上俩种执行方式,都不会影响线程池里面其他线程的正常执行。

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