// Atomic 變數自增運算測試(incrementAndGet 方法的原子性)
public class AtomicTest {
    public static AtomicInteger race = new AtomicInteger(0);
    
    public static void increase() {
        // 輸出正確結果，一切都要歸功於 incrementAndGet 方法的原子性
        race.incrementAndGet();  
    }
    
    public static final int THREADS_COUNT = 20;
    
    
 
public static void main(String[] args) throws Exception {
        Thread[] threads = new Thread[THREADS_COUNT];
        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread(new Runnable() {
                @Override
                public void run() {
                    
 
for (int j = 0; j < 10000; j++) {
                        increase();
                    }
                }
            });
            threads[i].start();
        }
        
        while(Thread.activeCount() > 1) {
            Thread.yield();
        }
        
        System.out.println(race);
    }
    
    
 
/**
     * incrementAndGet() 方法的JDK 原始碼
     * Atomically increment by one the current value.
     * @return the updated value
     */
    public final int incrementAndGet() {
        for(;;) {
            int current = get();
            int next = current + 1;
            if(compareAndSet(current,next)) {
                return next;
            }
        }
    }
}