线程在线程池执行时抛出异常会发生什么?
它会终止并被垃圾收集吗?
背景故事: 我时不时地使用
ScheduledThreadPoolExecutor
来运行任务,Netty 也在使用它。现在,使用此应用程序的客户告诉我,他们有时会注意到一堆客户端随机断开连接,每次发生这种情况时,都会记录来自单独的非 Netty 相关任务的堆栈跟踪。我的假设是线程被中断并被垃圾收集,因此 Netty 丢失了对线程的任何引用并断开分配的 tcp 客户端。
线程在线程池执行时抛出异常会发生什么?
这个问题的答案取决于代码是否使用
threadPool.execute(...)
或 threadPool.submit(...)
。如果您使用 execute(...)
并且任务抛出未捕获的异常,则线程终止,池会忘记该线程,并在适当的情况下立即启动另一个线程。任务和线程可以被垃圾收集。
如果您使用
submit(...)
,那么任务将完成,异常将被捕获,线程将继续运行,并将提交到线程池的下一个作业出队并执行它。您可以通过扩展 ThreadPoolExecutor
并覆盖来查看抛出的异常:
protected void afterExecute(Runnable r, Throwable t) { }
使用
submit(...)
,线程池捕获任务抛出的所有异常,以便它可以使用 Future
报告任务的状态。
它会终止并被垃圾收集吗?
如果使用
execute(...)
,那么是的,线程将终止,并且它和任务可以被垃圾收集。如果使用 submit(...)
,那么线程将不会终止,但任务可以被垃圾收集。现在,池可以通过不同的方式来决定减少在其中运行的线程数量,这可能会导致线程终止并可能导致垃圾收集。
...一堆客户端随机断开连接...
意味着有什么东西打扰了他们?或者您想知道它们是否抛出异常?如果一堆同时终止,似乎会发生其他事情。
我的假设是线程被中断并被垃圾收集,因此 Netty 丢失对线程的任何引用并断开分配的 tcp 客户端。
如果线程被中断,则有人正在对作业调用取消或正在关闭线程池。其他人不应该中断线程。无论如何,这不会导致线程终止和垃圾收集。如果线程被中断,任务当然可以继续运行,除非它抛出
RuntimeException
或其他异常。如果发生这种情况,一旦任务完成,线程池就会清除中断,并且线程从队列中提取下一个任务。
您可以使用以下代码查看异常处理:
public static void main(String[] args) {
ExecutorService threadPool = Executors.newFixedThreadPool(1);
// this thread will be killed and replaced
threadPool.execute(new Task());
// this thread will catch and handle exception and run the following task
threadPool.submit(new Task());
threadPool.submit(new Task());
}
private static class Task implements Runnable {
@Override
public void run() {
// this should print out the same thread ids even though the task threw
System.out.println(Thread.currentThread().getId());
throw new RuntimeException();
}
}
线程在线程池执行时抛出异常会发生什么?
它会终止并被垃圾收集吗?
如果死亡的线程将线程池大小减少到小于核心池大小,则立即创建一个新线程(因此您的旧线程将可用于垃圾回收)
见下面的代码:
当我创建一个核心池大小=“1”的线程池时,当我正在运行的线程抛出运行时异常时,会立即创建一个新线程。
当我创建一个 core pool size = "2" 的线程池时,当我正在运行的线程抛出运行时异常时,会立即创建一个新线程。
import java.util.Scanner;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ThreadExample1 {
private volatile ThreadPoolExecutor threadPoolExecutor;
public static void main(String[] args) throws InterruptedException {
ThreadExample1 threadExample1 = new ThreadExample1();
threadExample1.doTheWork();
}
private void doTheWork() throws InterruptedException {
Scanner scanner = new Scanner(System.in);
ThreadFactory myThreadFactory = new MyThreadFactory("task");
threadPoolExecutor = (ThreadPoolExecutor) Executors.newFixedThreadPool(2, myThreadFactory);
System.out.println("before task is sent to be executed: thread pool size: " + threadPoolExecutor.getPoolSize() + ", core pool size: " + threadPoolExecutor.getCorePoolSize() + " - threads active count: " + threadPoolExecutor.getActiveCount());
scanner.next();
threadPoolExecutor.execute(new MyTask());
System.out.println("immediately after task is sent to be executed: thread pool size: " + threadPoolExecutor.getPoolSize() + ", core pool size: " + threadPoolExecutor.getCorePoolSize() + " - threads active count: " + threadPoolExecutor.getActiveCount());
scanner.next();
System.out.println("going to sleep");
Thread.sleep(2000);
System.out.println("going to sleep");
System.out.println("after waking up");
System.out.println("after waking up: thread pool size: " + threadPoolExecutor.getPoolSize() + ", core pool size: " + threadPoolExecutor.getCorePoolSize() + " - threads active count: " + threadPoolExecutor.getActiveCount());
scanner.next();
threadPoolExecutor.shutdown();
threadPoolExecutor.awaitTermination(5, TimeUnit.SECONDS);
}
class MyThreadFactory implements ThreadFactory {
Logger logger = Logger.getLogger("MyThreadFactory");
private int counter = 0;
private String prefix = "";
public MyThreadFactory(String prefix) {
this.prefix = prefix;
}
@Override
public Thread newThread(Runnable r) {
counter++;
String name = prefix + "-" + counter;
logger.log(Level.WARNING, "thread: " + name + " - is going to be created");
System.out.println("before a new thread is created. pool size: " + threadPoolExecutor.getPoolSize() + ", core pool size: " + threadPoolExecutor.getCorePoolSize() + " - threads active count: " + threadPoolExecutor.getActiveCount());
return new Thread(r, name);
}
}
}
class MyTask implements Runnable {
Logger logger = Logger.getLogger("MyTask");
@Override
public void run() {
while (true) {
System.out.println("thread: " + Thread.currentThread().getName() + " - current state: " + Thread.currentThread().getState());
throw new RuntimeException("something bad happened");
}
}
}