垃圾收集器的Java命令行

Question

I am working on a Swing based java application. And my application will holds lots and lots of object in the memory and which leads to "Out Of Memory" error. I knew that my code broken somewhere and not handled the memory leaks.

When i was profiling my application, for a study, i have written a thread which will call System.gc() in a specific interval (example: for every 3 minutes) which was reducing the JVM used memory dramatically. I do understand that, the code was not written properly to clear the references of unused objects which giving this behavior.

I am looking into such memory leaks in my code, but still i am having two questions,

1. can i write such a thread which request for garbage collection? will it harm my application? i do accept, the performance will be reduced but its not worse than getting out of memory error.

2. Instead of creating a thread, is there any start-up command-line argument which will request for garbage collection for the given specific time interval.

Thanks in advance !!!

Answer 1

I do understand that, the code was not written properly to clear the references of unused objects which giving this behavior.

Actually, this is not a proper explanation of the behaviour you see.

Either your code releases references, or it does not.

As a result, the garbarge collector will be able to either reclaim memory, or it will not be able to (not matter how hard it tries or how often you run it).

That garbage collection happens at lengthly intervals during which you build up a lot of "used" memory is perfectly normal. Java will try very hard to reclaim memory before it will complain about OutOfMemory errors. Conversely, it will not try very hard if there is still free memory for you to use.

So unless you are seeing actual performance problems that result from GC taking too long, I would not worry about trying to tune it.

If what you are seeing are OutOfMemory errors, then GC tuning won't help you.

can i write such a thread which request for garbage collection? will it harm my application? i do accept, the performance will be reduced but its not worse than getting out of memory error.

Again, that tradeoff does not exist. You cannot avoid OOM by running GC more often.

And yes, unnecessary GC (which is what you would be doing here) is detrimental to performance.

Answer 2

First of all, Use on System#gc is not considered as a best practice.

I do understand that, the code was not written properly to clear the references of unused objects >which giving this behavior

Instead of running GC, try to spot the memory leaks and change your code accordingly. Calling System#gc will hamper your performance severely. I will advise you to revisit your application code.

edited: follow basic Java Programming practice to close resources and assign null to references which are no longer used, and many more.. you can easily find on google.

Answer 3

You can always download VisualVM profiler. It has an option "Perfom GC".