自己實現了一個類似AtomicInteger的原子類功能，反覆比較並交換，主要用到

• 反射獲取Unsafe及物件的靜態成員變數
• Unsafe獲取地址偏移量
• CAS

public class MyStudy {
    public static int data = 0; 
    public static void main(String[] args) throws Exception{
        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafe.setAccessible(true);
        Unsafe unsafe = (Unsafe) theUnsafe.get(null);
        long dataAddress = unsafe.staticFieldOffset(MyStudy.class.getDeclaredField("data"));
        for (int i = 0; i < 100; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int j = 0; j < 100; j++) {
                        int anInt = unsafe.getInt(MyStudy.class, dataAddress);
                        while(!unsafe.compareAndSwapInt(MyStudy.class,dataAddress,anInt,anInt+1))
                            anInt = unsafe.getInt(MyStudy.class, dataAddress);
                    }
                }
            }).start();
        }
        Thread.sleep(1000);
        System.out.println(data);
    }

}
 

執行結果10000。

Unsafe類需要使用獲取其靜態成員變數的方法來拿到，呼叫getUnsafe()會報錯，反射拿取建構函式就違背了Unsafe的初衷（多個Unsafe例項可能會造成執行緒不安全）。