import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;    

public final class ContextSwitchTest {
    static int RUNS = 1;
    static int ITERATES = 1000;
    static AtomicReference turn = new AtomicReference();

    static final class WorkerThread extends Thread {
        volatile Thread other;
        volatile int nparks;
        public void run() {
            final AtomicReference t = turn;
            final Thread other = this.other;
            
	    Thread current = Thread.currentThread();  
            System.out.println("Name : " + current.getName() +", " + current.getId( ));

            if (turn == null || other == null)
                throw new NullPointerException();
            int p = 0;
            for (int i = 0; i < ITERATES; ++i) {
                while (!t.compareAndSet(other, this)) {
                    LockSupport.park();
                    ++p;
                }
                LockSupport.unpark(other);
            }
            LockSupport.unpark(other);
            nparks = p;
            System.out.println("parks: " + p);

        }
    }

    static void test() throws Exception {
        WorkerThread a = new WorkerThread();
        WorkerThread b = new WorkerThread();
        a.other = b;
        b.other = a;
        turn.set(a);
        long startTime = System.nanoTime();
        a.start();
        b.start();
        a.join();
        b.join();
        long endTime = System.nanoTime();
        int parkNum = a.nparks + b.nparks;
        System.out.println("Average time: " + ((endTime - startTime) / parkNum)
                           + "ns");
    }

    public static void main(String[] args) throws Exception {
	if (args.length != 2) {
                System.out.println("Usage: \n" +
                                   "java -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints  ContextSwitchTest  <number of RUNS>  <lock ITERATES>");
                System.out.println("Example: \n" +
                                   "java -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints  ContextSwitchTest 1 1000000");
                System.exit(0);
        }
        if (args.length == 2) {
		RUNS = Integer.parseInt(args[0]);
    		ITERATES = Integer.parseInt(args[1]);
	}

        System.out.println("RUNS : " + RUNS + ", ITERATES : " + ITERATES);
	long startTime = System.nanoTime();
        for (int i = 0; i < RUNS; i++) {
            test();
        }
        long endTime = System.nanoTime();
        System.out.println("Total time: " + ((endTime - startTime)) + "ns = " + (endTime - startTime) / 1000000000 + "s");
    }
}