generate CPU load in Java

Question

I am conducting some throughput testing. My application has to

1. read from JMS
2. do some processing
3. write to JMS

My goal here is t

Answer 1

Create a matrix and do a couple of matrix manipulations.

You can tune that pretty easily by varying the size of the matrix.

Answer 2

Yet another stuff you can use, maybe :

        long start  = System.currentTimeMillis();
        long count = 0l;
        for(long x=0;x<Integer.MAX_VALUE ;x++){
            count+=1;
        }
        long end = System.currentTimeMillis();
        System.out.println(end-start +" ms");

Answer 3

Encrypt a string (in a loop) by calling Cipher.update(). Encryption algorithms are by definition very difficult to optimize. The only problem is that there is some non-trivial setup you need to perform. I'm marking this answer as community wiki, so that somebody who's written it recently can fill it in.

Answer 4

You could try something simple like

private static void spin(int milliseconds) {
    long sleepTime = milliseconds*1000000L; // convert to nanoseconds
    long startTime = System.nanoTime();
    while ((System.nanoTime() - startTime) < sleepTime) {}
}

Test:

public static void main(String[] args) {
    final int NUM_TESTS = 1000;
    long start = System.nanoTime();
    for (int i = 0; i < NUM_TESTS; i++) {
        spin(500);
    }
    System.out.println("Took " + (System.nanoTime()-start)/1000000 +
        "ms (expected " + (NUM_TESTS*500) + ")");
}

My output:

$ java SpinTest
Took 500023ms (expected 500000)

So the loop didn't get optimized away (and yeah, I spiked my CPU to 100% for eight minutes just to test this :)).

Answer 5

Create a very large collection of random objects and then alternate calls to Collections.shuffle() and Collections.sort().

I used Jakarta Commons Lang to generate random strings for the purposes of shuffling/sorting.