OptimisticLock.java

package common_problem;

import sun.misc.Unsafe;

import java.io.Serializable;

/**
 * 乐观锁
 *
 * @author JunjunYang
 * @date 2020/1/8 21:46
 */
public class OptimisticLock {
 /**
 * 版本号实现
 *
 * @return
 */
 static class AccountService {
 public boolean transAccount(int delta) {
// "select version,account from account where id = A";
// compute account;
// "update account set account=#{account},version=version+1 where version=#{version} and id = A"
 return true;
 }
 }

 /**
 * CAS实现
 */
 static class AtomicInteger implements Serializable {
 private volatile int value;
 private static final Unsafe unsafe = Unsafe.getUnsafe();
 private static final long valueOffset;

 static {
 try {
 valueOffset = unsafe.objectFieldOffset(AtomicInteger.class.getDeclaredField("value"));
 } catch (Exception e) {
 throw new Error(e);
 }
 }

 public int increateAndGet() {
 for (; ; ) {
 int cur = value;
 int next = value + 1;
 if (unsafe.compareAndSwapInt(this, valueOffset, cur, next))
 return next;
 }
 }
 }
}