几类常见的锁机制

• Optimistic Offline Lock
• Pessimistic Offline Lock
• Coarse-Grained Lock
• Implicit Lock

具体的代码如下：

Optimistic Offline Lock:

最常用的方法：associate a version number with each record in your system：版本号

额外的信息：最后修改时间、修改人

In addition to a version number for each record, storing information as to who last modified a record and when can be quite useful when managing concurrency conflicts.

注意：使用系统时间是不好的做法，因为系统时间不可靠、特别是用于多个系统之间

乐观锁的使用列子：

There's one system using Optimistic Offline Locks that we all should be familiar with: source code management (SCM).

乐观锁的适用场景：

Optimistic concurrency management is appropriate when the chance of conflict between any two business transactions is low.