Question

Without using Quartz, is there any option for Timer class or workaround to start scheduled jobs even if the previous job is not finished?

Here’s sample code.

Job Scheduled for every 1 sec

public static void main(String[] args) {
  Timer timer = new Timer();
  Calendar date = Calendar.getInstance();
  timer.scheduleAtFixedRate(new UnitTest(timer), date.getTime(), 1000);
}

Job Performed

Each job has 2 second delay

public void run() {
    count++;
    int a = count; // to see which job is started and ended.
    System.out.println(this.now("HH:mm:ssSSS")+"- start "+count);
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {}
    System.out.println(this.now("HH:mm:ssSSS")+"- end "+a);
}

Result – if the previous job is not finished, then the next job is not started.

12:14:21946 - start 1
12:14:23965 - end 1
12:14:23965 - start 2
12:14:25966 - end 2
12:14:25967 - start 3
12:14:27968 - end 3
12:14:27968 - start 4
12:14:29969 - end 4
12:14:29970 - start 5
12:14:31970 - end 5
12:14:31971 - start 6
12:14:33972 - end 6

How can I add this option for Timer class?

Quartz – Concurrent Option from http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/scheduling.html

By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering with each other. If you specify two triggers for the same JobDetail, it might be possible that before the first job has finished, the second one will start. If JobDetail classes implement the Stateful interface, this won’t happen. The second job will not start before the first one has finished. To make jobs resulting from the MethodInvokingJobDetailFactoryBean non-concurrent, set the concurrent flag to false.

EDITED SAMPLE CODE

public class TEST01 {

Timer timerTEST01 = new Timer();

public String[] start()
{
    try
    {
        timerTEST01.scheduleAtFixedRate(new TimerTask() {
            public void run() {
                Runnable r = new Runnable() {
                    public void run() {
                        //DoWork
                    }
                };
                Thread t = new Thread(r);
                t.start();
            }

        }, date.getTime(), 1000*60);

        return new String[]{"true", "Good Job!"};
    }
    catch(Exception e){}
    finally{}
}
}

Answer 1

Instead of running the code directly at the timer, when the timer calls your method, spawn a new thread (or use a thread poll) to execute your task:

public void run() {
    Runnable r = new Runnable() {
        public void run() {
            count++;
            int a = count; // to see which job is started and ended.
            System.out.println(this.now("HH:mm:ssSSS")+"- start "+count);
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {}
            System.out.println(this.now("HH:mm:ssSSS")+"- end "+a);
        }
    };

    Thread t = new Thread(r);
    t.start();
}

This will guarantee that every single job executes at the given time even if the previous one hasn’t executed.

Also, make sure your code works inside an anonymous inner class, that count++ probably isn’t going to work.