通过创建子进程，使得父子进程之间可以通信，使用了信号量，和共享内存变量。- A little program ,fork four subprocess that Communication with the parent process,used posix shared a database by shared memory method

Linux 下 的信号量编程，保证的用户进程的正常调度-Semaphores under Linux programming, to guarantee the normal operation of a user process