Why does ScheduledExecutorService.schedule(Runnable r, Long delay, TimeUnit t) ignore the delay and runs instantly?

Question

I have a ScheduledExecutorService that I want to use to schedule the execution of a Runnable with a certain delay. However, when I call its schedule method the delay is completely ignored and the Runnable is executed instantly. This is my code:

My ScheduledExecutorService constructor:

    private static ScheduledExecutorService existQueuePool = Executors.newScheduledThreadPool(1);

and this is the call to its schedule method (surrounded by Logs):

Log.d(TAG,"Before schedule");
ScheduledFuture<?> mScheduledFuture = existQueuePool.schedule(new Runnable() {
                    @Override
                    public void run() {
                        Log.d(TAG,"Setting clearMessageTask for exist messages in the existQueuePool.");                       
                        clearMessageTask(mContext.getString(R.string.existType));
                    }
                }, 1000L, TimeUnit.MILLISECONDS);
Log.d(TAG,"After schedule");

The logs allow me to see that there's only a 20-30ms delay between the "Before schedule" and the "Setting clear...", instead of 1000ms as I was expecting.

The documentation on the schedule method reads:

Creates and executes a one-shot action that becomes enabled after the given delay.

What does the term "enable" exactly mean in this context?

Any help will be greatly appreciated.

EDIT: Even when using a Long (1000L), the code seems to execute immediately.

Answer 1

I think you have it right. Try 1000L, as a long value is expected, instead of an int.

Edit: Tried it myself, and your code works for me:

package testdelay;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

public class TestDelay {

    private static final ScheduledExecutorService existQueuePool = Executors.newScheduledThreadPool(1);
    private static long start;
    private static long end;
    public static void main(String[] args) {
        start = System.currentTimeMillis();
        System.out.println("Before execution: " + start);
        ScheduledFuture<?> mScheduledFuture = existQueuePool.schedule(new Runnable() {
                    @Override
                    public void run() {
                        end = System.currentTimeMillis();
                        System.out.println("Executed at: " + end);
                        System.out.println("Executed after delay of : " + (end - start) + " ms.");
                    }
                }, 1000L, TimeUnit.MILLISECONDS);
    }
}

Output:

Before execution: 1386350613147
Executed at: 1386350614149
Executed after delay of : 1002 ms.

It appears that it runs instantaneously because you log a message outside of the runnable, which is executed right after the submission to the service. You should log it in the runnable itself to see when it is ran.