ExecutorService's surprising performance break-even point — rules of thumb?

Question

I\'m trying to figure out how to correctly use Java\'s Executors. I realize submitting tasks to an ExecutorService has its own overhead. However, I\'m surpris

Answer 1

Math.random() actually synchronizes on a single Random number generator. Calling Math.random() results in significant contention for the number generator. In fact the more threads you have, the slower it's going to be.

From the Math.random() javadoc:

This method is properly synchronized to allow correct use by more than one thread. However, if many threads need to generate pseudorandom numbers at a great rate, it may reduce contention for each thread to have its own pseudorandom-number generator.