在UNIX系统编程过程中，一个进程往往需要等待多个描述字发生某一事件，如可读、可写或异常等等。进程不能永远地等待其中任何单独一个描述字，它需要同时等待所有描述字，此时就是IO复用技术，系统调用select就是实现这一目标的方式之-In the UNIX system programming process, a process often have to wait more than describe the character of an event, such as read, write or exception may be so. Process can not always wait for a descr iption of any single word, it needs while waiting for word of all descr iptions, and at that point IO multiplexing, select system call is a way of achieving this goal