How can I synchronize a jBatch execution?

Question

I'm writing a jBatch program with jBeret. I am currently doing like this.

final JobOperator operator = BatchRuntime.getJobOperator();
logger.debug("operator: {}", operator);

final long id = operator.start("some", null);
logger.debug("id: {}", id);

final JobExecution execution = operator.getJobExecution(id);
logger.debug("execution: {}", execution);

The problem is that execution seems run asynchronously and the main method simply returns.

The best I can do is looping until exit status is not null.

String status;
while ((status = execution.getExitStatus()) == null) {
    //logger.debug("sleeping");
    Thread.sleep(1000L);
}
logger.debug("status: {}", status);

Is there any other way to do this?

Answer 1

If you need to block-and-wait, as you've described, there is no other option, but have something like awaiCompletion() implemented.

Your looping approach can be improved. Let's use ThreadPoolExecutor as an example. It has the following method:

    /**
     * Blocks until all tasks have completed execution after a shutdown
     * request, or the timeout occurs, or the current thread is
     * interrupted, whichever happens first.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return {@code true} if this executor terminated and
     *         {@code false} if the timeout elapsed before termination
     * @throws InterruptedException if interrupted while waiting
     */
    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;

and here is the implementation:

    public boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (;;) {
                if (runStateAtLeast(ctl.get(), TERMINATED))
                    return true;
                if (nanos <= 0)
                    return false;
                nanos = termination.awaitNanos(nanos);
            }
        } finally {
            mainLock.unlock();
        }
    }

Please note:

• infinite loop should always have exit condition defined
• in your case timeout is must-have, because it is unlikely you are ready for an endless wait
• naturally you have to know whether it was timeout or job termination

So, here is an adapted version:

    public static boolean awaitTermination(JobExecution execution, long timeout) throws InterruptedException {
        final long limit = System.currentTimeMillis() + timeout;
        for (;;) {
            if (null != execution.getExitStatus()) {
                return true;
            }

            if (System.currentTimeMillis() >= limit) {
                return false;
            }

            Thread.sleep(timeout/10);            
        }
    }

Answer 2

You could implement the JobListener class, or just extend AbstractJobListener:

...
public class MyJobListener extends AbstractJobListenerJobListener {

    // The afterJob method receives control after the job execution ends.
    @Override
    public void afterJob() throws Exception { ... }

    ...
}

And in the afterJob method you could use some basic Java synchronization technique (Future or so).

Answer 3

JBeret has an internal method:

org.jberet.runtime.JobExecutionImpl#awaitTermination(long timeout, TimeUnit timeUnit);

for that purpose.

When running with JBeret, you can call that method on the JobExecution obtained from starting the job.