package wat;

public class ThreadContention {
	public static void main(String[] args) throws InterruptedException {
		// dummy thread to get the HotSpot VM to compile OpThread.op()
		Thread opThread = new OpThread(1048576L);
		opThread.start();
		opThread.join();

		// real benchmarks
		benchmark(2, 80000000L);
		benchmark(64, 2500000L);
	}

	private static void benchmark(final int numThreads,
			final long iterationsEach) throws InterruptedException {
		Thread[] threads = new Thread[numThreads];
		for (int i = 0; i < threads.length; i++)
			threads[i] = new OpThread(iterationsEach);
		long startTime = System.currentTimeMillis();
		for (int i = 0; i < threads.length; i++)
			threads[i].start();
		for (int i = 0; i < threads.length; i++)
			threads[i].join();
		long duration = System.currentTimeMillis() - startTime;
		System.out.println(numThreads + " ran in " + duration + " millsec");
	}

	static class OpThread extends Thread {
		private final long iterations;

		private final int[] temp = { 0xCAFEBABE, 0xCAFEBABE, 0xCAFEBABE,
				0xCAFEBABE }; // ;)

		private volatile int cur = 0;

		public OpThread(long iterations) {
			this.iterations = iterations;
		}

		@Override
		public void run() {
			for (long iteration = 0; iteration < iterations; iteration++) {
				temp[(cur + 1) % temp.length] = op(temp[cur]);
				cur = (cur + 1) % temp.length;
			}
		}

		private int op(final int value) {
			// some random operation that doesn't involve I/O or
			// garbage collection, but does involve memory access
			return Integer.rotateLeft(value ^ 0x1337BEEF * 7
					+ (int) ((float) value / 1.337357f / Math.random()), 16) | 0xAA005500;
		}
	}
}