select是用于監(jiān)視多個(gè)文件描述符狀態(tài)的變化的。即用來(lái)監(jiān)視文件描述符讀/寫/異常狀態(tài)是否就緒。
函數(shù)原型:int select(int nfds,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,struct timeval *timeout);
select的幾大缺點(diǎn):
(1)每次調(diào)用select,都需要把fd集合從用戶態(tài)拷貝到內(nèi)核態(tài),這個(gè)開(kāi)銷在fd很多時(shí)會(huì)很大
(2)同時(shí)每次調(diào)用select都需要在內(nèi)核遍歷傳遞進(jìn)來(lái)的所有fd,這個(gè)開(kāi)銷在fd很多時(shí)也很大
(3)select支持的文件描述符數(shù)量太小了
??1?#include<stdio.h> ??2?#include<string.h> ??3?#include<stdlib.h> ??4?#include<unistd.h> ??5?#include<sys> ??6? ??7?int?main() ??8?{ ??9?????int?std_in?=?0; ?10?//??int?std_out?=?1; ?11?????fd_set?reads; ?12?//??fd_set?writes; ?13?????//int?max_nums?=?std_out; ?14?????int?max_nums?=?std_in; ?15?????FD_ZERO(&reads); ?16?//??FD_ZERO(&writes); ?17?????FD_SET(std_in,&reads); ?18?//??FD_SET(std_out,&writes); ?19?????struct?timeval?_timeout?=?{5,0}; ?20?????int?done?=?0; ?21?????while(!done) ?22?????{ ?23?????????_timeout.tv_sec?=?5; ??24?????????_timeout.tv_usec?=?0; ?25?????????//switch(select(max_nums+1,&reads,&writes,NULL,&_timeout)) ?26?????????switch(select(max_nums+1,&reads,NULL,NULL,&_timeout)) ?27?????????{ ?28?????????????case?-1: ?29?????????????????perror("select"); ?30?????????????????break; ?31?????????????case?0: ?32?????????????????printf("timeout...n"); ?33?????????????????break; ?34?????????????default://success ?35?????????????????{ ?36?????????????????????if(FD_ISSET(std_in,&reads)) ?37?????????????????????{//read ?38?????????????????????????char?buf[1024]; ?39?????????????????????????memset(buf,' 久久久99精品一区二区| 久久人人爽人人爽人人AV| 精品999久久久久久中文字幕| 久久人人爽爽爽人久久久| 97精品久久天干天天天按摩| 狠狠色丁香久久综合五月| 久久久久国产视频电影| 99久久99久久精品国产片果冻 | 亚洲国产日韩综合久久精品| 婷婷久久香蕉五月综合加勒比| 国产午夜久久影院| 模特私拍国产精品久久| 精品免费tv久久久久久久| 久久综合亚洲色一区二区三区| 情人伊人久久综合亚洲| 亚洲国产美女精品久久久久∴| 精品久久久久久无码中文字幕 | 丁香五月综合久久激情| 伊人久久大香线蕉AV色婷婷色 | 久久精品国产一区| 久久久久精品国产亚洲AV无码| 国产精品热久久毛片| 久久精品国产亚洲av麻豆色欲 | 性做久久久久久久久久久| jizzjizz国产精品久久| 久久免费看黄a级毛片| 亚洲国产天堂久久久久久| 精品久久久久久久久久中文字幕| 久久99国产乱子伦精品免费| 思思久久精品在热线热| 热综合一本伊人久久精品| 国产AV影片久久久久久| 青青草国产精品久久| 久久久国产精品福利免费| 99久久99久久久精品齐齐| 欧美午夜精品久久久久免费视| 国产激情久久久久久熟女老人| 精品久久久久久国产| 久久久久久精品免费看SSS| 久久人妻无码中文字幕| 久久免费的精品国产V∧ |