Error java.lang.OutOfMemoryError: GC overhead limit exceeded

Question

I get this error message as I execute my JUnit tests:

java.lang.OutOfMemoryError: GC overhead limit exceeded

I know what an OutOfMemo

Answer 1

It's usually the code. Here's a simple example:

import java.util.*;

public class GarbageCollector {

    public static void main(String... args) {

        System.out.printf("Testing...%n");
        List list = new ArrayList();
        for (int outer = 0; outer < 10000; outer++) {

            // list = new ArrayList(10000); // BAD
            // list = new ArrayList(); // WORSE
            list.clear(); // BETTER

            for (int inner = 0; inner < 10000; inner++) {
                list.add(Math.random());
            }

            if (outer % 1000 == 0) {
                System.out.printf("Outer loop at %d%n", outer);
            }

        }
        System.out.printf("Done.%n");
    }
}

Using Java 1.6.0_24-b07 on a Windows 7 32 bit.

java -Xloggc:gc.log GarbageCollector

Then look at gc.log

• Triggered 444 times using BAD method
• Triggered 666 times using WORSE method
• Triggered 354 times using BETTER method

Now granted, this is not the best test or the best design but when faced with a situation where you have no choice but implementing such a loop or when dealing with existing code that behaves badly, choosing to reuse objects instead of creating new ones can reduce the number of times the garbage collector gets in the way...