Why is parallel stream slower?

Question

I was playing around with infinite streams and made this program for benchmarking. Basically the bigger the number you provide, the faster it will finish. However, I was ama

Answer 1

The cost of passing work to multiple thread is expensive es the first time you do it. This cost is fairly fixed so even if your task is trivial, the overhead is relatively high.

One of the problems you have is that highly inefficient code is a very poor way to determine how well a solution performs. Also, how it runs the first time and how it runs after a few seconds can often be 100x different (can be much more) I suggest using an example which is already optimal and only then attempt to use multiple threads.

e.g.

long start = System.nanoTime();
int value = (int) (Math.random() * (target+1L));
long time = System.nanoTime() - value;
// don't time IO as it is sooo much slower
System.out.println(value);

Note: this will not be efficient until the code has warmuped and been compiled. i.e. ignore the first 2-5 seconds this code is run.