fork函数注意点： 1，与IO的缓冲机制！ 2，vfork与fork的不同：1，子进程先与父进程运行，2，子进程在父进程空间运行-fork Function NOTE points: 1, and IO buffer mechanism! 2, vfork and fork of the difference: 1, sub-processes to run first with the parent process, 2, the child process the parent p