1. 通過epoll實現高併發服務器模型
LT(level triggered)是缺省的工作方式,並且同時支持block和no-block socket.在這種做法中,內核告訴你一個文件描述符是否就緒了,然後你可以對這個就緒的fd進行IO操作。如果你不作任何操作,內核還是會繼續通知你的,所以,這種模式編程出錯誤可能性要小一點。傳統的select/poll都是這種模型的代表.
ET (edge-triggered)是高速工作方式,只支持no-block socket。如果一直不對這個fd作IO操作(從而導致它再次變成未就緒),內核不會發送更多的通知(only once)
#include "socket_includes.h"
#include <unistd.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <errno.h>
int mz_ipv4_tcp_create_socket(void)
{
int listenfd, sockfd, opt = 1;
struct sockaddr_in server, client;
socklen_t len;
int timep;
int ret;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
if(listenfd < 0){
perror("Create socket fail.");
return -1;
}
if((ret = setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))) < 0){
perror("Error, set socket reuse addr failed");
return -1;
}
bzero(&server, sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(SERV_PORT);
server.sin_addr.s_addr = htonl(INADDR_ANY);
len = sizeof(struct sockaddr);
if(bind(listenfd, (struct sockaddr *)&server, len)<0){
perror("bind error.");
return -1;
}
listen(listenfd, MAX_LISTEN_QUE);
return listenfd;
}
int mz_process_data(int sockfd)
{
int bytes;
char buf[100];
char *s = buf;
char flag = 1;
int len;
while(flag){
bytes = recv(sockfd, s, 5, 0);
if(bytes < 0){
if(errno == EAGAIN){
printf("no data.\n");
break;
}
perror("recv err:");
return -1;
}
if(bytes == 0){
return -2;
}
if(bytes == 5){
flag = 1;
}else {
flag = 0;
}
s += bytes;
len += bytes;
printf("bytes:%d\n", bytes);
//sleep(2);
}
printf("buf:%s\n", buf);
send(sockfd, buf, len, 0);
return 0;
}
int main(int argc, char *argv[])
{
int listenfd, sockfd;
int epollfd, fds;
struct epoll_event ev, events[MAX_EVENTS];
int i, rv;
struct sockaddr_in client;
int len;
len = sizeof(struct sockaddr_in);
epollfd = epoll_create(MAX_EVENTS);
if(epollfd < 0){
perror("epoll_create err:");
return -1;
}
listenfd = mz_ipv4_tcp_create_socket();
fcntl(listenfd, F_SETFL, O_NONBLOCK);
ev.data.fd = listenfd;
ev.events = EPOLLIN;
rv = epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev);
if(rv < 0){
perror("epoll_ctl err:");
return -1;
}
while(1){
//time_out
fds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
if(fds < 0){
perror("epoll_wait err:");
return -1;
}
for(i = 0; i < fds; i++){
if(events[i].data.fd == listenfd){
sockfd = accept(listenfd, (struct sockaddr *)&client, &len);
if(sockfd < 0){
perror("accept err:");
continue;
}
ev.data.fd = sockfd;
ev.events = EPOLLIN | EPOLLET;
epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev);
continue;
}else{
rv = mz_process_data(events[i].data.fd);
if(rv == -2){
epoll_ctl(epollfd, EPOLL_CTL_DEL, events[i].data.fd, &ev);
close(events[i].data.fd);
continue;
}
}
}
}
}
2. 併發編程方法比較:
a. ache模型,Process Per Connection,簡稱PPC;TPC,Thread Per Connection模型
各做各的事情
b. select / poll 模型之select
能做的事情有限,FD_SETSIZE/1024,也可以修改
效率問題,線性掃描的方法,嚴重影響;
內核,用戶空間內存拷貝
poll除了低一點,其他基本一致
c. epoll:select反過來就是epoll的好處了
能處理的鏈接數:#cat /proc/sys/fs/file-max //10W
效率問題:epoll只關注活躍的連接
內存拷貝:共享內存