Java高性能编程-线程安全-1.2.2原子操作
CAS机制的使用
AtomicInteger 就是对 unsafe 类进行封装
手动实现
import java.lang.reflect.Field; import sun.misc.Unsafe; public class CounterUnsafe { volatile int i = 0; private static Unsafe unsafe = null; // i字段的偏移量 private static long valueOffset; static { try { Field field = Unsafe.class.getDeclaredField("theUnsafe"); field.setAccessible(true); unsafe = (Unsafe) field.get(null); Field fieldi = CounterUnsafe.class.getDeclaredField("i"); valueOffset = unsafe.objectFieldOffset(fieldi); } catch (NoSuchFieldException | IllegalAccessException e) { e.printStackTrace(); } } public void add() { for (;;) { int current = unsafe.getIntVolatile(this, valueOffset); if (unsafe.compareAndSwapInt(this, valueOffset, current, current + 1)) break; } } }
运行
public class Demo1_CounterTest { public static void main(String[] args) throws InterruptedException { final CounterUnsafe ct = new CounterUnsafe(); for (int i = 0; i < 6; i++) { new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub for (int j = 0; j < 1000; j++) { ct.add(); System.out.println("dome..."); } } }).start(); Thread.sleep(6000L); System.out.println(ct.i); } } }