Question

We’ve developed a Java standalone program. We’ve configured in our Linux (RedHat ES 4) cron
schedule to execute this Java standalone every 10 minutes. Each standalone
may sometime take more than 1 hour to complete, or sometime it may complete
even within 5 minutes.

My problem/solution I’m looking for is, the number of Java standalones executing
at any time should not exceed, for example, 5 process. So, for example,
before even a Java standalone/process starts, if there are already 5 processes running,
then this process should not be started; otherwise this would indirectly start
creating OutOfMemoryError problems. How do I control this? I would also like to make this 5 process limit configurable.

Other Information:
I’ve also configured -Xms and -Xmx heap size settings.

Is there any tool/mechanism by which we can control this?

I also heard about Java Service Wrapper. What is this all about?

Answer 1

First, I am assuming you are using the words “thread” and “process” interchangably. Two ideas:

1. Have the cron job be a script that will check the currently running processes and count them. If less than threshold spawn new process, otherwise exit, here threshold can be defined in your script.
2. Have the main method in your executing java file check some external resource (a file, database table, etc) for a count of running processes, if it is below threshold increment and start process, otherwise exit (this is assuming the simple main method will not be enough to cause your OOME problem). You may also need to use an appropriate locking mechanism on the external resource (though if your job is every 10 minutes, this may be overkill), here you could defin threshold in a .properties, or some other configuration file for your program.