How to get the interrupted status of a terminated Java Thread?

Question

I'm trying to determine if a Java Thread was interrupted or not at the time that it terminated. So far the answer seems to be "no"...

Right before falling off the end of run() we can see Thread.currentThread().isInterrupted() is true.

But after join()ing the target thread we always get false:

import static org.junit.Assert.*;
import org.junit.Test;

public class ThreadDeadInterruptStateTest {
    @Test public void test() {
        Thread a = new Thread(new Runnable() {
            @Override public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                } finally {
                    // 2x to show that check doesn't reset status
                    assertTrue("Interrupt status from a 1: ",  // pass
                            Thread.currentThread().isInterrupted());
                    assertTrue("Interrupt status from a 2: ",  // pass
                            Thread.currentThread().isInterrupted());
                }
            }});
        a.start();
        a.interrupt();
        try {
            a.join();
            assertEquals("Thread state", a.getState(),
                    Thread.State.TERMINATED);  // pass
            assertTrue("Interrupt status after join: ",
                    a.isInterrupted());  // Still FAILs :-(
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

    public static void main(String[] args) {
        new ThreadDeadInterruptStateTest().test();
    }
}

Answer 1

You're checking the wrong thread's status:

Thread.currentThread().isInterrupted()

is the status of the main thread, because you execute it directly inside the test method. You didn't interrupt this one, you interrupted a. So, check a's status:

a.isInterrupted()