AtomicInteger例子

AtomicInteger可以保证原子性，可见性，有序性

public class AtomicIntegerTest {
    
    private static AtomicInteger  value =  new AtomicInteger();

    public static void main(String[] args) throws InterruptedException {

        Thread t1 = new Thread(new LoopVolatile());
        t1.start();

        Thread t2 = new Thread(new LoopVolatile2());
        t2.start();

        t1.join();
        t2.join();
        System.out.println("final val is: " + value); //20000
    }

    private static class LoopVolatile implements Runnable {
        public void run() {
            long val = 0;
            while (val < 10000L) {
                value.getAndIncrement();
                val++;
            }
        }
    }

    private static class LoopVolatile2 implements Runnable {
        public void run() {
            long val = 0;
            while (val < 10000L) {
                value.getAndIncrement();
                val++;
            }
        }
    }
}

 getAndIncrement方法是线程安全的，是由Unsafe类来保证线程安全的。

public final int getAndIncrement() {
          return unsafe.getAndAddInt(this, valueOffset, 1);
}