【Protecting the Cocoa Frameworks】
For multithreaded applications, Cocoa frameworks use locks and other forms of internal synchronization to ensure they behave correctly. To prevent these locks from degrading performance in the single-threaded case, however, Cocoa does not create them until the application spawns its first new thread using the NSThread class. If you spawn threads using only POSIX thread routines, Cocoa does not receive the notifications it needs to know that your application is now multithreaded. When that happens, operations involving the Cocoa frameworks may destabilize or crash your application.
To let Cocoa know that you intend to use multiple threads, all you have to do is spawn a single thread using the NSThread class and let that thread immediately exit. Your thread entry point need not do anything. Just the act of spawning a thread using NSThread is enough to ensure that the locks needed by the Cocoa frameworks are put in place.
If you are not sure if Cocoa thinks your application is multithreaded or not, you can use the isMultiThreaded method of NSThread to check.
【保护Cocoa框架】
为了让Cocoa知道你将使用多线程，所有你需要做的就是用NSThread创建一个线程，然后让线程立即退出。这样就能让Cocoa框架知转换到多线程状态下。
通过NSThread类的isMultiThreaded方法，可以查看当前Cocoa线程状态。
【Mixing POSIX and Cocoa Locks】
It is safe to use a mixture of POSIX and Cocoa locks inside the same application. Cocoa lock and condition objects are essentially just wrappers for POSIX mutexes and conditions. For a given lock, however, you must always use the same interface to create and manipulate that lock. In other words, you cannot use a Cocoa NSLock object to manipulate a mutex you created using thepthread_mutex_init function, and vice versa.
【混合POSIX和Cocoa锁】
Cocoa Lock只是POSIX Lock的封装，你不能用NSLock对象去操作用pthread_mutex_init函数产生的mutex。