This is my java code.
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
class ExceptionThread2 implements Runnable {
@Override
public void run() {
Thread t = Thread.currentThread();
System.out.println("run() by " + t);
System.out.println("eh = " + t.getUncaughtExceptionHandler());
throw new RuntimeException();
}
}
class MyUncaughtExceptionHandler implements Thread.UncaughtExceptionHandler {
@Override
public void uncaughtException(Thread t, Throwable e) {
System.out.println("caught " + e);
}
}
class HandlerThreadFactory implements ThreadFactory {
@Override
public Thread newThread(Runnable r) {
System.out.println(this + " creating new Thread ");
Thread t = new Thread(r);
System.out.println("created " + t);
t.setUncaughtExceptionHandler(new MyUncaughtExceptionHandler());
System.out.println("eh = " + t.getUncaughtExceptionHandler());
return t;
}
}
public class CaptureUncaughtException {
public static void main(String[] args) {
ExecutorService exec = Executors.newCachedThreadPool(new HandlerThreadFactory());
exec.execute(new ExceptionThread2());
//exec.shutdown();
}
}
The result:
com.concurrent.example.HandlerThreadFactory@7f31245a creating new Thread
created Thread[Thread-0,5,main]
eh = com.concurrent.example.MyUncaughtExceptionHandler@6d6f6e28
run() by Thread[Thread-0,5,main]
eh = com.concurrent.example.MyUncaughtExceptionHandler@6d6f6e28
com.concurrent.example.HandlerThreadFactory@7f31245a creating new Thread
created Thread[Thread-1,5,main]
eh = com.concurrent.example.MyUncaughtExceptionHandler@2870fdbb
caught java.lang.RuntimeException
When I uncomment //exec.shutdown()
the result is different. Only one thread is created.
com.concurrent.example.HandlerThreadFactory@7f31245a creating new Thread
created Thread[Thread-0,5,main]
eh = com.concurrent.example.MyUncaughtExceptionHandler@6d6f6e28
run() by Thread[Thread-0,5,main]
eh = com.concurrent.example.MyUncaughtExceptionHandler@6d6f6e28
caught java.lang.RuntimeException
Why?
Your runnable crashes its thread. So the pool will replace that thread with a new one (for the next task you might submit).
If the pool is already being shut down, it will not do that.
When you do:
exec.execute(new ExceptionThread2());
A worker thread is created and executes your task.
But it complete abnormally and dying after throw exception.
In this case, thread pool create another worker to replace the dead one, hence you see two created
message but only one run()
message
Here is the runWorker
which execute your task:
* 1. We may start out with an initial task, in which case we
* don't need to get the first one. Otherwise, as long as pool is
* running, we get tasks from getTask. If it returns null then the
* worker exits due to changed pool state or configuration
* parameters. Other exits result from exception throws in
* external code, in which case completedAbruptly holds, which
* usually leads processWorkerExit to replace this thread.
final void runWorker(Worker w)
- Other exits result from exception throws in external code, in which case completedAbruptly holds, which usually leads processWorkerExit to replace this thread
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