说明：  利用共享内存实现多线程间通信。 主线程派生子线程后即处于休眠状态，等待子线程结束时发出结束信号唤醒。在被唤醒后，主线程向屏幕输出结束信息！ 线程A向共享内存中写入A~Z的大写字母。 线程B通过共享内存接收这些字母，并将其保存到/test.dat文件中。 注意线程之间的同步互斥！
(Using shared memory communication between multi-threading. Derived from sub-thread after main thread is in sleep mode, waiting for the end of the child issued by the end of the thread wake-up signal. After being awakened, the main thread to the end of the output information on the screen! Thread A writes to the shared memory, A ~ Z of the capital letters. Thread B through shared memory to receive these letters, and save it to/test.dat file. Note that the synchronization between threads mutually exclusive!)