java unsafe compareandswap 并发

interface  {
    void increment();
    long getCounter();
}

static class CASCounter implements  {
	private volatile long counter = 0;
	private Unsafe unsafe;
	private long offset;
	public CASCounter() throws Exception {
		unsafe = getUnsafe();
		offset = unsafe.objectFieldOffset(CASCounter.class.getDeclaredField("counter"));
	}
	
	public void increment() {
		long before = counter;
		while (!unsafe.compareAndSwapLong(this, offset, before, before + 1)) {
			before = counter;
		}
	}
	
	public long getCounter() {
		return counter;
	}
}
static class AtomicCounter implements  {
	AtomicLong counter = new AtomicLong(0);
	
	public void increment() {
		counter.incrementAndGet();
	}
	
	public long getCounter() {
		return counter.get();
	}
}
static class LockCounter implements  {
	private volatile long counter = 0;
	private WriteLock lock = new ReentrantReadWriteLock().writeLock();
	
	public void increment() {
		lock.lock();
		counter++;
		lock.unlock();
	}
	@Override
	public long getCounter() {
		return counter;
	}
}
static class SyncCounter implements  {
	private volatile long counter = 0;
	@Override
	public synchronized void increment() {
		counter++;
	}
	@Override
	public long getCounter() {
		return counter;
	}
}
static class StupidCounter implements Counter {
	private volatile long counter = 0;
	@Override
	public void increment() {
		counter++;
	}
	@Override
	public long getCounter() {
		return counter;
	}
}
static class CounterClient implements Runnable {
	private volatile Counter c;
	private int num;
	public CounterClient(Counter c, int num) {
		this.c = c;
		this.num = num;
	}
	@Override
	public void run() {
		for (int i = 0; i < num; i++) {
			c.increment();
		}
	}
}

public static void main(String[] args) throws Exception {
	int NUM_OF_THREADS = 200;
	int NUM_OF_INCREMENTS = 100000;
	ExecutorService service = Executors.newFixedThreadPool(NUM_OF_THREADS);
	Counter counter = null;
	counter = new StupidCounter(); 
	// Counter result: 2087134
	// Time passed in ms:469
	counter = new SyncCounter(); 
	// Counter result: 10000000
	// Time passed in ms:1407
	counter = new LockCounter(); 
	// Counter result: 10000000
	// Time passed in ms:1259
	counter = new AtomicCounter(); 
	// Counter result: 10000000
	// Time passed in ms:3361
	counter = new CASCounter(); 
	// Counter result: 10000000
	// Time passed in ms:3939
	long before = System.currentTimeMillis();
	for (int i = 0; i < NUM_OF_THREADS; i++) {
		service.submit(new CounterClient(counter, NUM_OF_INCREMENTS));
	}
	service.shutdown();
	service.awaitTermination(1, TimeUnit.MINUTES);
	long after = System.currentTimeMillis();
	System.out.println("Counter result: " + counter.getCounter());
	System.out.println("Time passed in ms:" + (after - before));
}