Java并发编程之CAS的案例分析

import sun.misc.Unsafe;
import java.lang.reflect.Field;

public class UnsafeUtil {
 public static Unsafe reflectGetUnsafe() {
  try {
   Field field = Unsafe.class.getDeclaredField("theUnsafe");
   field.setAccessible(true);
   return (Unsafe) field.get(null);
  } catch (Exception e) {
   e.printStackTrace();
  }
  return null;
 }
}

import com.walking.juc.util.UnsafeUtil;
import sun.misc.Unsafe;
public class AtomicState {
 private volatile int state = 0;
 public int getState() {
  return state;
 }

 private static final Unsafe UNSAFE = UnsafeUtil.reflectGetUnsafe();
 private static final long offsetState;
 static {
  try {
   offsetState = UNSAFE.objectFieldOffset(AtomicState.class.getDeclaredField("state"));
  } catch (NoSuchFieldException e) {
   throw new Error(e);
  }
 }
 public final boolean compareAndSetState(int oldVal, int newVal) {
  return UNSAFE.compareAndSwapInt(this, offsetState, oldVal, newVal);
 }
}

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
@Slf4j
public class TestAtomicState {

 static int tNum = 5;//线程数 我们开10个线程模拟多线程并发
 static CyclicBarrier cyclicBarrier = new CyclicBarrier(tNum);//栅栏
 static CountDownLatch countDownLatch = new CountDownLatch(tNum);//计数器
 static AtomicState atomicState = new AtomicState();

 public static void main(String[] args) throws InterruptedException {
  for (int i = 1; i <= tNum; i++) {
   new Thread(new MyTask(),"t-"+i).start();
  }
  countDownLatch.await();//为的是让主线程在这句阻塞住，等待所有线程执行完毕(计数器减到0)再往下走
  log.info("state最后的值:" + atomicState.getState());
 }

 static class MyTask implements Runnable{
  @Override
  public void run() {
   try {
    log.info(Thread.currentThread().getName() + "到达起跑线");
    String name = Thread.currentThread().getName();
    String substring = name.substring(name.indexOf("-") + 1);
    int i1 = Integer.parseInt(substring);

    cyclicBarrier.await();//设置一个屏障，所有线程达到这后开始一起往下执行 模拟并发
    boolean b = atomicState.compareAndSetState(0, i1);
    if (b) {
     log.info("修改成功，tName:{}" ,Thread.currentThread().getName());
    } else {
     log.info("修改失败，tName:{}" ,Thread.currentThread().getName());
    }
   } catch (InterruptedException | BrokenBarrierException e) {
    e.printStackTrace();
   } finally {
    countDownLatch.countDown();//线程执行完毕计数器减一
   }
  }
 }
}

import java.util.concurrent.atomic.AtomicInteger;
@Slf4j
public class CAS_ABA_Stampe {
 static AtomicInteger atomicInteger = new AtomicInteger(10);
 public static void main(String[] args) throws InterruptedException {
  Thread t1 = new Thread(() -> {
   try {
    log.info("{}拿到state的值为:{}", Thread.currentThread().getName(), atomicInteger.get());
    log.info("{}第一次修改", Thread.currentThread().getName());
    atomicInteger.getAndSet(0);
    Thread.sleep(2000);
    log.info("{}第二次修改", Thread.currentThread().getName());
    atomicInteger.getAndSet(10);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }, "t1");
  t1.start();

  Thread t2 = new Thread(() -> {
   try {
    log.info("{}第一次拿到state的值为:{}", Thread.currentThread().getName(), atomicInteger.get());
    Thread.sleep(2500);
    log.info("{}第二次拿到state的值为:{}", Thread.currentThread().getName(), atomicInteger.get());
    log.info("{}开始修改state的值为2", Thread.currentThread().getName());
    atomicInteger.getAndSet(20);
    log.info("{}修改成功", Thread.currentThread().getName());
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }, "t2");
  t2.start();
  t1.join();
  t2.join();
  log.info("最终state的值:{}", atomicInteger.get());
 }
}

import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.atomic.AtomicStampedReference;

@Slf4j
public class CAS_ABA_Stampe {
 static AtomicStampedReference<Integer> stampedReference = new AtomicStampedReference<>(10, 1);

 public static void main(String[] args) throws InterruptedException {
  Thread t1 = new Thread(() -> {
   try {
    int stamp = stampedReference.getStamp();
    int intValue = stampedReference.getReference().intValue();
    log.info("{}私挪公款拿到stamp的值为:{}，余额:{}", Thread.currentThread().getName(), stamp,intValue);
    stampedReference.compareAndSet(10, 0, stamp, stamp + 1);
    Thread.sleep(2000);
    stamp = stampedReference.getStamp();
    intValue = stampedReference.getReference().intValue();
    log.info("{}还回公款拿到stamp的值为:{}，余额:{}", Thread.currentThread().getName(), stamp,intValue);
    stampedReference.compareAndSet(0, 10, stamp, stamp + 1);
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }, "t1");
  t1.start();

  Thread t2 = new Thread(() -> {
   try {
    int stamp = stampedReference.getStamp();
    int intValue = stampedReference.getReference().intValue();
    log.info("{}拿到stamp的值为:{}，余额:{}", Thread.currentThread().getName(), stamp, intValue);
    Thread.sleep(3000);

    log.info("{}开始存款", Thread.currentThread().getName());
    if (stampedReference.compareAndSet(10, 20, stamp, stamp + 1)) {
     log.info("{}款款成功", Thread.currentThread().getName());
    }else {
     log.info("{}存款失败，发现账户异常!!oldStamp:{},currentStamp:{}", Thread.currentThread().getName(),stamp,stampedReference.getStamp());
    }
   } catch (InterruptedException e) {
    e.printStackTrace();
   }
  }, "t2");
  t2.start();
  t1.join();
  t2.join();
  log.info("最终账户余额:{}W", stampedReference.getReference().intValue());
 }
}