5种io模型
tcp服务器分为了5种io复用模型,分别是:
阻塞io模型
非阻塞io模型
io复用
信号驱动io
异步io
本文会讲前面3种io模型的tcp服务器实现(本文只做tcp服务器实现,客户端逻辑处理,接收数据等缓冲区不做深入说明)
简单实现
首先，我们需要理解下tcp服务器的创建过程：
1:通过socket函数创建一个套接字文件
2:通过bind函数将本地一个地址和套接字捆绑
3:使用listen函数监听外部请求
4:使用accept函数接收外部请求
5:read,write,close 用于收,发,关闭客户端数据
好了,我们了解了tcp服务器的创建过程,就开始实现吧:
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#define BUFFER_SIZE 1024
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
while (1) {
str_length = read(client_socket, buffer, BUFFER_SIZE);
if (str_length == 0) //读取数据完毕关闭套接字
{
close(client_socket);
printf("连接已经关闭: %d \n", client_socket);
break;
} else {
printf("客户端发送数据:%s",buffer);
write(client_socket, buffer, str_length);//发送数据
}
}
return 0;
}
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多客户端TCP服务器
以上代码实现了一个服务器,并且可以接收一个客户端连接,和它互相收发信息,但是看代码很容易发现不支持多客户端,只支持一个,那么怎么才能实现支持多个客户端呢?我们稍微改一改这份代码:
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#define BUFFER_SIZE 1024
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
size_t client_arr[100];//存储客户端数组
int client_length=0;//记录客户端数量
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
while (1) {
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
client_arr[client_length] = client_socket;
client_length++;
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
for (int i = 0; i < client_length; ++i) {
if (client_arr[i]==0){
continue;
}
str_length = read(client_arr[i], buffer, BUFFER_SIZE);
if (str_length == 0) //读取数据完毕关闭套接字
{
close(client_arr[i]);
client_arr[i]=0;
printf("连接已经关闭: %d \n", client_arr[i]);
break;
} else {
printf("客户端发送数据:%s",buffer);
write(client_arr[i], buffer, str_length);//发送数据
}
}
}
}
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我们通过将client_socket存储到一个数组里,然后每次去遍历该数组,可以勉强实现一个所谓的多客户端tcp服务器,但是有个致命弱点:
由于accept,read函数是阻塞的,导致这份代码,每次运行都得客户端连接,才能到下面的遍历代码,导致代码根本就没什么卵用:
A客户端连接好了,然后发送了条消息,服务器还得等到B客户端连接,才能接收到A的消息
,然后,B客户端发送好消息,需要C客户端连接,然后还得A客户端发送了条消息,才能遍历到B客户端的消息
多进程TCP服务器
这样的话,这份代码根本没什么卵用啊!!!!!!该怎么解决这个问题呢?????
我们或许可以通过多进程去解决这个问题,每个进程只处理一条客户端,就不存在什么阻塞不阻塞的问题了:
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#include<sys/wait.h>//waitpid();
#define BUFFER_SIZE 1024
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
int str_length;
pid_t pid;
int status = 0;//初始化状态
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
while (1) {
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
pid = fork();
if (pid > 0) {
sleep(1);//父进程,进行下次循环,读取客户端连接事件
waitpid(-1, &status, WNOHANG | WUNTRACED | WCONTINUED);
if (WIFEXITED(status)) {
printf("status = %d\n", WEXITSTATUS(status));
}
if (WIFSIGNALED(status)) { //如果子进程是被信号结束了 ，则为真
printf("signal status = %d\n", WTERMSIG(status));
//R->T
}
if (WIFSTOPPED(status)) {
printf("stop sig num = %d\n", WSTOPSIG(status));
}
//T->R
if (WIFCONTINUED(status)) {
printf("continue......\n");
}
} else if (pid == 0) {//子进程,进行阻塞式收发客户端数据
while (1) {
memset(buffer, 0, sizeof(buffer));
str_length = read(client_socket, buffer, BUFFER_SIZE);
if (str_length == 0) //读取数据完毕关闭套接字
{
close(client_socket);
printf("连接已经关闭: %d \n", client_socket);
exit(1);
} else {
printf("%d 客户端发送数据:%s \n", client_socket, buffer);
write(client_socket, buffer, str_length);//发送数据
}
}
break;
} else {
printf("创建子进程失败\n");
exit(1);
}
}
return 0;
}
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通过多进程,我们可以实现一个较完美的多进程TCP服务器,这个服务器可以完美的去处理多个客户端的数据
但是,一个进程处理一个连接,如果连接多的时候,会造成进程的频繁创建销毁,进程开销会非常大,导致cpu占用太大
所以,直接使用多进程去处理,还是不够完美的
由第二个例子,我们可以发现,主要问题出在于accept,read函数的阻塞上面,有没有什么办法处理掉这个阻塞呢?
非阻塞式TCP服务器
在c语言中,可以使用fcntl函数,将套接字设置为非阻塞的
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#include <fcntl.h>//非阻塞
#define BUFFER_SIZE 1024
int set_non_block(int socket) {
int flags = fcntl(socket, F_GETFL, 0);
flags |= O_NONBLOCK;
return fcntl(socket, F_SETFL, flags);
}
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
size_t client_arr[100];//存储客户端数组
int client_length = 0;//记录客户端数量
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
if (set_non_block(server_socket) == -1) {//设置非阻塞
printf("设置非阻塞失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
while (1) {
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
if (client_socket > 0) {//非阻塞下,无法读取返回-1
client_arr[client_length] = client_socket;
client_length++;
if (set_non_block(client_socket) == -1) {//设置非阻塞
printf("设置客户端非阻塞失败\n");
exit(1);
}
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
}
for (int i = 0; i < client_length; ++i) {
if (client_arr[i] == 0) {
continue;
}
memset(&buffer, 0, sizeof(buffer));
str_length = read(client_arr[i], buffer, BUFFER_SIZE);
if (str_length==-1){//非阻塞下,无法读取返回-1
continue;
}
if (str_length == 0) //读取数据完毕关闭套接字
{
close(client_arr[i]);
client_arr[i] = 0;
printf("连接已经关闭: %d \n", client_arr[i]);
break;
} else {
printf("客户端发送数据:%s", buffer);
write(client_arr[i], buffer, str_length);//发送数据
}
}
usleep(100);//非阻塞下,如果全部socket无法读取(没有事件变化),则相当于是while(1),会使cpu繁忙
}
}
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这样,我们就实现了一个单进程多客户端的tcp服务器了,不需要多进程也能实现多客户端,但是看最后一行注释能发现一个问题:非阻塞下,会无限循环,让代码空转,这样浪费的性能也是巨大的,那我们该怎么完善呢?或许我们可以用到I/O复用模型
select机制TCP服务器
select是系统级别的功能,它可以同时阻塞探测多个socket,并且返回可调用的socket的数量
原理图大概为:
实现代码:
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#define BUFFER_SIZE 1024
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
fd_set reads,copy_reads;
int fd_max,fd_num;
struct timeval timeout;
FD_ZERO(&reads);//初始化清空socket集合
FD_SET(server_socket,&reads);
fd_max=server_socket;
while (1) {
copy_reads = reads;
timeout.tv_sec = 5;
timeout.tv_usec = 5000;
//无限循环调用select 监视可读事件
if((fd_num = select(fd_max+1, ©_reads, 0, 0, &timeout)) == -1) {
perror("select error");
break;
}
if (fd_num==0){//没有变动的socket
continue;
}
for(int i=0;i<fd_max+1;i++){
if(FD_ISSET(i,©_reads)){
if (i==server_socket){//server_socket变动,代表有新客户端连接
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
FD_SET(client_socket,&reads);
if(fd_max < client_socket){
fd_max=client_socket;
}
}else{
memset(buffer, 0, sizeof(buffer));
str_length = read(i, buffer, BUFFER_SIZE);
if (str_length == 0) //读取数据完毕关闭套接字
{
close(i);
printf("连接已经关闭: %d \n", i);
FD_CLR(i, &reads);//从reads中删除相关信息
} else {
printf("%d 客户端发送数据:%s \n", i, buffer);
write(i, buffer, str_length);//将数据发送回客户端
}
}
}
}
}
return 0;
}
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上面就是select机制的tcp实现代码,可以同时处理多客户端,性能比多进程好了很多,但这并不是说明select机制没有缺点了
在这份代码中,可以发现以下几点:
1:客户端的socket标识符是存在一个fd_set类型中的集合中的,客户端大小由fd_set大小决定,开发时需要考虑到这个的最大值
2:每次调用select函数之前,都得将集合重新传给select,效率较慢;
3:每次调用完select函数,就算返回1,也会将集合全部遍历一遍,效率较慢
epoll机制TCP服务器
原理图大概为:
epoll机制提供了以下3个核心函数:
epoll_create() 创建epoll监听socket
epoll_ctl()注册,删除,修改监听
epoll_wait() 等待事件触发函数
在实现epoll机制前,我们得先了解下ET/LT模式
LT(level-trigger) 水平触发
epoll的默认工作方式,在这个模式下,只要监听的socket有可读/可写状态,都将返回该socket,例如:
当客户端给tcp服务器发送一个数据时,这个client_socket将会是可读的,调用epoll_wait函数将会返回该client_socket,
如果服务器不做处理,这个client_socket将会是一直可读的,下次调用epoll_wait函数将会继续返回client_socket
实现代码:
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#include <sys/epoll.h> //epoll
#define BUFFER_SIZE 1024
#define CLIENT_MAX_SIZE 1024
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
struct epoll_event event;//监听事件
struct epoll_event wait_event_list[CLIENT_MAX_SIZE];//监听结果
int fd[CLIENT_MAX_SIZE];
int j = 0;
int epoll_fd = epoll_fd = epoll_create(10);//创建epoll句柄,里面的参数10没有意义
if (epoll_fd == -1) {
printf("创建epoll句柄失败\n");
exit(1);
}
event.events = EPOLLIN;//可读事件
event.data.fd = server_socket;//server_socket
int result = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event);
if (result == -1) {
printf("注册epoll 事件失败\n");
exit(1);
}
while (1) {
result = epoll_wait(epoll_fd, wait_event_list, CLIENT_MAX_SIZE, -1);//阻塞
if (result <= 0) {
continue;
}
for (j = 0; j < result; j++) {
printf("%d 触发事件 %d \n", wait_event_list[j].data.fd, wait_event_list[j].events);
//server_socket触发事件
if (server_socket == wait_event_list[j].data.fd && EPOLLIN == wait_event_list[j].events & EPOLLIN) {
addr_size = sizeof(client_addr);
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
event.data.fd = client_socket;
event.events = EPOLLIN;//可读或错误
result = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event);
if (result == -1) {
printf("注册客户端 epoll 事件失败\n");
exit(1);
}
continue;
}
//客户端触发事件
if ((wait_event_list[j].events & EPOLLIN)
||(wait_event_list[j].events & EPOLLERR))//可读或发生错误
{
memset(&buffer, 0, sizeof(buffer));
str_length = read(wait_event_list[j].data.fd, buffer, BUFFER_SIZE);
if (str_length == 0) //读取数据完毕关闭套接字
{
close(wait_event_list[j].data.fd);
event.data.fd = wait_event_list[j].data.fd;
epoll_ctl(epoll_fd, EPOLL_CTL_DEL, wait_event_list[j].data.fd, &event);
printf("连接已经关闭: %d \n", wait_event_list[j].data.fd);
} else {
printf("客户端发送数据:%s \n", buffer);
write(wait_event_list[j].data.fd, buffer, str_length);//执行回声服务 即echo
}
}
}
}
// return 0;
}
|
lt模式下,也可以使用非阻塞模式,以上代码未使用
ET(edge-trigger) 边缘触发
通过注册监听增加EPOLLET参数可将模式转换成边缘触发,
在et模式下,socket触发的多个事件只会返回一次,必须一次性全部处理,例如:
server_socket 有10个待处理的新连接,在epoll_wait函数返回后,必须循环读取accept直到没有数据可读,
由于必须一直循环读取,所以当accept没有数据可读时,必须是非阻塞模式,否则会阻塞
实现代码
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#include <stdio.h>
#include <arpa/inet.h>//inet_addr() sockaddr_in
#include <string.h>//bzero()
#include <sys/socket.h>//socket
#include <unistd.h>
#include <stdlib.h>//exit()
#include <sys/epoll.h> //epoll
#define BUFFER_SIZE 1024
#define CLIENT_MAX_SIZE 1024
int set_non_block(int socket) {
int flags = fcntl(socket, F_GETFL, 0);
flags |= O_NONBLOCK;
return fcntl(socket, F_SETFL, flags);
}
int main() {
char listen_addr_str[] = "0.0.0.0";
size_t listen_addr = inet_addr(listen_addr_str);
int port = 8080;
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t addr_size;
char buffer[BUFFER_SIZE];//缓冲区大小
int str_length;
server_socket = socket(PF_INET, SOCK_STREAM, 0);//创建套接字
bzero(&server_addr, sizeof(server_addr));//初始化
server_addr.sin_family = INADDR_ANY;
server_addr.sin_port = htons(port);
server_addr.sin_addr.s_addr = listen_addr;
if (bind(server_socket, (struct sockaddr *) &server_addr, sizeof(server_addr)) == -1) {
printf("绑定失败\n");
exit(1);
}
if (listen(server_socket, 5) == -1) {
printf("监听失败\n");
exit(1);
}
printf("创建tcp服务器成功\n");
set_non_block(server_socket);//设置非阻塞
struct epoll_event event;//监听事件
struct epoll_event wait_event_list[CLIENT_MAX_SIZE];//监听结果
int fd[CLIENT_MAX_SIZE];
int j = 0;
int epoll_fd = epoll_fd = epoll_create(10);//创建epoll句柄,里面的参数10没有意义
if (epoll_fd == -1) {
printf("创建epoll句柄失败\n");
exit(1);
}
event.events = EPOLLIN|EPOLLET;//注册可读事件+et模式
event.data.fd = server_socket;//server_socket
int result = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, server_socket, &event);
if (result == -1) {
printf("注册epoll 事件失败\n");
exit(1);
}
while (1) {
result = epoll_wait(epoll_fd, wait_event_list, CLIENT_MAX_SIZE, -1);//阻塞
if (result <= 0) {
continue;
}
for (j = 0; j < result; j++) {
printf("%d 触发事件 %d \n", wait_event_list[j].data.fd, wait_event_list[j].events);
//server_socket触发事件
if (server_socket == wait_event_list[j].data.fd && EPOLLIN == wait_event_list[j].events & EPOLLIN) {
addr_size = sizeof(client_addr);
while(1) {
client_socket = accept(server_socket, (struct sockaddr *) &client_addr, &addr_size);
if(client_socket==-1){//没有数据可读
break;
}
printf("%d 连接成功\n", client_socket);
char msg[] = "恭喜你连接成功";
write(client_socket, msg, sizeof(msg));
set_non_block(client_socket);//设置非阻塞
event.data.fd = client_socket;
event.events = EPOLLIN|EPOLLET;//可读+et模式
result = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, client_socket, &event);
if (result == -1) {
printf("注册客户端 epoll 事件失败\n");
exit(1);
}
}
continue;
}
//客户端触发事件
if ((wait_event_list[j].events & EPOLLIN)
||(wait_event_list[j].events & EPOLLERR))//可读或发生错误
{
memset(&buffer, 0, sizeof(buffer));
while(1){
str_length = read(wait_event_list[j].data.fd, buffer, BUFFER_SIZE);
//读取多次数据
if(str_length==-1){//没有数据返回
break;
}
if (str_length == 0) //读取数据完毕关闭套接字
{
close(wait_event_list[j].data.fd);
event.data.fd = wait_event_list[j].data.fd;
epoll_ctl(epoll_fd, EPOLL_CTL_DEL, wait_event_list[j].data.fd, &event);
printf("连接已经关闭: %d \n", wait_event_list[j].data.fd);
} else {
printf("客户端发送数据:%s \n", buffer);
write(wait_event_list[j].data.fd, buffer, str_length);//执行回声服务 即echo
}
}
}
}
}
// return 0;
}
|
以上说明,可看出:
1:epoll不需要遍历其他没有事件的socket,避免了select的性能浪费
2:epoll有两种工作模式,用于不同的场景,et和lt模式都可以用非阻塞,但et模式必须非阻塞,et模式编程难度较大,每次epoll_wait都得考虑必须处理掉所有事件
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