[英]Task execution with ExecutorService: Can I submit task within another task?
我想在出现故障(异常)的情况下在现有任务中提交一个新任务,但在运行以下代码时遇到了一些问题:
public class TestTask implements Runnable{
private int myInt;
private ExecutorService exec;
public TestTask(int x, ExecutorService s){
this.myInt=x;
this.exec=s;
}
@Override
public void run() {
try{
//print number if it's odd; otherwise throw exception
if(this.myInt%2 ==0) throw new Exception();
else System.out.println("Asynchronous task: "+ this.myInt); //do sth
} catch (Exception e) {
System.out.println("resubmitting..");
//## TODO: PROBLEM??
this.exec.execute(new TestTask(this.myInt+1, this.exec));
}
}
public static void main(String[] args) {
int NTHREADS =2;
final ExecutorService service= Executors.newFixedThreadPool(NTHREADS);
//run tasks
for(int i=0; i<10; i++){
service.execute(new TestTask(i, service) );
}
//...
}
//....
代码编译并运行几步,然后抛出java.util.concurrent.RejectedExecutionException 。 任何想法如何解释这个以及如何解决? 谢谢!
resubmitting..
Asynchronous task: 1
resubmitting..
Asynchronous task: 3
resubmitting..
Asynchronous task: 5
resubmitting..
Exception in thread "pool-1-thread-2" java.util.concurrent.RejectedExecutionException: Task pe.ads.TestTask@4e19b97c rejected from java.util.concurrent.ThreadPoolExecutor@322ba3e4[Shutting down, pool size = 2, active threads = 2, queued tasks = 8, completed tasks = 3]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at pe.ads.TestTask.run(TestTask.java:26)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Exception in thread "pool-1-thread-1" java.util.concurrent.RejectedExecutionException: Task pe.ads.TestTask@31eb494e rejected from java.util.concurrent.ThreadPoolExecutor@322ba3e4[Shutting down, pool size = 2, active threads = 2, queued tasks = 8, completed tasks = 3]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at pe.ads.TestTask.run(TestTask.java:26)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Asynchronous task: 7Exception in thread "pool-1-thread-3" java.util.concurrent.RejectedExecutionException: Task pe.ads.TestTask@35afe17b rejected from java.util.concurrent.ThreadPoolExecutor@322ba3e4[Shutting down, pool size = 2, active threads = 2, queued tasks = 6, completed tasks = 6]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at pe.ads.TestTask.run(TestTask.java:26)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
resubmitting..
Asynchronous task: 9
Asynchronous task: 1
Exception in thread "pool-1-thread-5" java.util.concurrent.RejectedExecutionException: Task pe.ads.TestTask@53e64a3b rejected from java.util.concurrent.ThreadPoolExecutor@322ba3e4[Shutting down, pool size = 2, active threads = 2, queued tasks = 3, completed tasks = 8]
resubmitting..
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at pe.ads.TestTask.run(TestTask.java:26)
Asynchronous task: 1 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
结果我在 for 循环之后立即调用了 shutdown(),
for(int i=0; i<10; i++){
service.execute(new TestTask(i, service) );
}
service.shutdown();
所以新提交的任务被拒绝了。 还了解到 ThreadPoolExecutor 是一个更好的选择。 谢谢你们!
您可以ThreadPoolExecutor
并在其中包含重新提交逻辑。 会更优雅。 ThreadPoolExecutor
设计精良,并提供钩子方法来做你需要的。 你想覆盖ThreadPoolExecutor.afterExecute
不看代码我们无法判断,但很可能您在隐藏代码中执行了这两件事之一(甚至可能在main
),并且您必须修复它(顺便说一句,此行为可以使用setRejectedExecutionHandler
自定义)
我不知道这个问题是您的实际问题还是示例问题,但无论如何,我认为一个任务产生另一个任务并不是常见的做法。 你最好重构你的代码,让调用者自己在必要时提交一个新任务。 并不是说它会解决您的问题,而是肯定会改进您的程序设计。 如果您描述了您的域,也许我们也可以提供帮助。
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