c++11中有一个区域锁lock_guard，还有第二个区域锁unique_lock。
区域锁lock_guard使用起来比较简单，除了构造函数外没有其他member function，在整个区域都有效。
区域锁unique_guard除了lock_guard的功能外，提供了更多的member_function，相对来说更灵活一些。
unique_guard的最有用的一组函数为：
| locks the associated mutex (public member function) |
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| tries to lock the associated mutex, returns if the mutex is not available (public member function) |
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attempts to lock the associated TimedLockable mutex, returns if the mutex has been unavailable for the specified time duration (public member function) |
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tries to lock the associated TimedLockable mutex, returns if the mutex has been unavailable until specified time point has been reached (public member function) |
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| unlocks the associated mutex |
通过上面的函数，可以通过lock/unlock可以比较灵活的控制锁的范围，减小锁的粒度。
通过try_lock_for/try_lock_until则可以控制加锁的等待时间，此时这种锁为乐观锁。
本文转自 jiu~ 博客园博客，原文链接：http://www.cnblogs.com/jiu0821/p/7269777.html，如需转载请自行联系原作者
