正确应用系统调用signal()建立进程与信号（异步事件）之间的联系，理解信号机制；

正确应用系统调用getppid()、kill(),进步理解广义同步的含义。

-The correct application of the system call signal () to establish processes and signal (asynchronous events) the link between understanding the signaling mechanisms　the proper application of the system call getppid (), kill (), progress in understanding the meaning of generalized synchronization.