Question

I have a loop that spawns a lot of threads. These threads contains, among other things, 2 (massive) StringBuilder objects. These threads then run and do their thing.

However, I noticed that after a certain amount of threads, I get strange crashes. I know this is because of these StringBuilder, because when I reduce their initial capacity, I can start a lot more threads. Now for these StringBuilders, they are create like this in the constructor of the thread object:

StringBuilder a = new StringBuilder(30000);
StringBuilder b = new StringBuilder(30000);

The point where it generally crashes is around 550 threads, which results in a little bit more than 62MB. Combined with the rest of the program the memory in use is most likely 64MB, which I read online somewhere was the defaulf size of the JVM memory allocation pool. I don’t know whether this is true or not.

Now, is there something I am doing wrong, that somehow because of the design, I am allocating memory the wrong way? Or is this the only way and should I tell the JVM to increase its memory pool? Or something else entirely?

Also, please do not tell me to set a lower capacity, I know these StringBuilders automatically increase their capacity when needed, but I would like to have a solution to this problem.

Answer 1

Use the -Xmx JVM option to increase the Java maximum heap size.

Before J2SE 5.0, the default maximum heap size was 64MB. You can override this default using the -Xmx command-line option.