source: benchmark/ctxswitch/JavaThread.java@ bbe3719

public class JavaThread {
        // Simplistic low-quality Marsaglia Shift-XOR pseudo-random number generator.
        // Bijective
        // Cycle length for non-zero values is 4G-1.
        // 0 is absorbing and should be avoided -- fixed point.
        // The returned value is typically masked to produce a positive value.
        static volatile int Ticket = 0 ;

        private static int nextRandom (int x) {
                if (x == 0) {
                        // reseed the PRNG
                        // Ticket is accessed infrequently and does not constitute a coherence hot-spot.
                        // Note that we use a non-atomic racy increment -- the race is rare and benign.
                        // If the race is a concern switch to an AtomicInteger.
                        // In addition accesses to the RW volatile global "Ticket"  variable are not
                        // (readily) predictable at compile-time so the JIT will not be able to elide
                        // nextRandom() invocations.
                        x = ++Ticket ;
                        if (x == 0) x = 1 ;
                }
                x ^= x << 6;
                x ^= x >>> 21;
                x ^= x << 7;
                return x ;
        }
        static int x = 2;

        static private long times = Long.parseLong("100000");

        public static void helper() {
                for(long i = 1; i <= times; i += 1) {
                        Thread.yield();
                }
        }
        public static void InnerMain() {
                long start = System.nanoTime();
                helper();
                long end = System.nanoTime();
                System.out.println( (end - start) / times );
        }
        public static void main(String[] args) throws InterruptedException {
                if ( args.length > 1 ) System.exit( 1 );
                if ( args.length == 1 ) { times = Long.parseLong(args[0]); }

                for (int i = Integer.parseInt("5"); --i >= 0 ; ) {
                        InnerMain();
                        Thread.sleep(2000);     // 2 seconds
                        x = nextRandom(x);
                }
                if ( x == 0 ) System.out.println(x);
        }
}

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