Is it possible to force an existing Java application to use no more than x cores?

We are benchmarking existing Java programs. They are threaded applications designed to benefit from multi-core CPUs. We would like to measure the effect of the number of cores on the running speed, but we are unwilling (and unable) to change the code of these applications.

Of course, we could test the software on different machines, but this is expensive and complicated. We would rather have a software solution.

Note: you can assume that the testing platform is either Windows, Linux or Mac. Ideally, we would like to be able to run the tests on either of these platforms.

It's called setting CPU affinity, and it's an OS setting for processes, not specific to Java.

On Linux: http://www.cyberciti.biz/tips/setting-processor-affinity-certain-task-or-process.html

On Windows: http://www.addictivetips.com/windows-tips/how-to-set-processor-affinity-to-an-application-in-windows/

On Mac it doesn't look like you can set it: https://superuser.com/questions/149312/how-to-set-processor-affinity-on-os-x