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,' 18禁黄久久久AAA片| 97久久国产露脸精品国产| 久久精品中文字幕有码| 久久亚洲综合色一区二区三区 | 波多野结衣中文字幕久久| 99国产精品久久久久久久成人热| 国产精品伦理久久久久久| 久久久久国产精品嫩草影院| 久久99热精品| 奇米影视7777久久精品| 欧美久久一级内射wwwwww.| 国产情侣久久久久aⅴ免费| 欧美亚洲另类久久综合| 亚洲欧美日韩精品久久亚洲区 | 久久99精品久久久久久9蜜桃 | 99久久综合国产精品二区| 亚洲午夜福利精品久久| A狠狠久久蜜臀婷色中文网| 久久天天日天天操综合伊人av| 久久精品国产久精国产| 精品久久久久久无码不卡| 久久久久国产一级毛片高清版| 2021国产精品久久精品| 国产成人精品久久亚洲| 精品综合久久久久久97| 国产精品成人精品久久久| 久久亚洲精品成人AV| 午夜视频久久久久一区 | 精品久久久久久综合日本| 99精品国产综合久久久久五月天 | 亚洲精品99久久久久中文字幕| 精品久久久久久无码专区| 色综合久久久久无码专区| 亚洲午夜久久久久妓女影院| 久久无码精品一区二区三区| 99热成人精品免费久久| 狠色狠色狠狠色综合久久 | 久久影视综合亚洲| 亚洲精品高清久久| 久久久久亚洲AV综合波多野结衣| 久久精品国产亚洲网站|