epoll中et+多线程模式中很重要的EPOLL

本文主要是介绍epoll中et+多线程模式中很重要的EPOLL_ONESHOT实验，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

因为et模式需要循环读取，但是在读取过程中，如果有新的事件到达，很可能触发了其他线程来处理这个socket，那就乱了。

EPOLL_ONESHOT就是用来避免这种情况。注意在一个线程处理完一个socket的数据，也就是触发EAGAIN errno时候，就应该重置EPOLL_ONESHOT的flag，这时候，新到的事件，就可以重新进入触发流程了。

注：EPOLL_ONESHOT的原理其实是，每次触发事件之后，就将事件注册从fd上清除了，也就不会再被追踪到；下次需要用epoll_ctl的EPOLL_CTL_MOD来手动加上才行。

服务器代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <assert.h>#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <pthread.h>#define MAX_EVENT_NUMBER 1024
#define BUFFER_SIZE 1024
struct fds {int epollfd;int sockfd;
};int setnonblocking(int fd) {int old_option = fcntl(fd, F_GETFL);int new_option = old_option | O_NONBLOCK;fcntl(fd, F_SETFL, new_option);return old_option;
}void addfd(int epollfd, int fd, bool oneshot) {epoll_event event;event.data.fd = fd;event.events = EPOLLIN | EPOLLET;if (oneshot) {event.events |= EPOLLONESHOT;}epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);setnonblocking(fd);
}void reset_oneshot(int epollfd, int fd) {epoll_event event;event.data.fd = fd;event.events = EPOLLIN | EPOLLET | EPOLLONESHOT;epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &event);
}void* worker(void *arg) {int sockfd = ((fds*)arg)->sockfd;int epollfd = ((fds*)arg)->epollfd;pthread_t pid = pthread_self();printf("start new thread %u to recv data on fd: %d\n", pid, sockfd);char buf[BUFFER_SIZE];memset(buf, '\0', BUFFER_SIZE);while(1) {int ret = recv(sockfd, buf, BUFFER_SIZE-1, 0);if (ret == 0) {close(sockfd);printf("foreiner closed the connection\n");break;}else if (ret < 0) {if (errno == EAGAIN) {reset_oneshot(epollfd, sockfd);printf("EAGAIN read later\n");break;}}else {buf[ret] = '\0';printf("thread %u get content: %s\n", pid, buf);printf("thread %u about to sleep\n", pid);sleep(5);printf("thread %u back from sleep\n", pid);}}//printf("end thread %u receiving data on fd: %d\n", pid, sockfd);

}int main(int argc, char *argv[]) {if (argc <= 1) {printf("usage: %s port_number [ip_address]\n", basename(argv[0]));return 1;}int port = atoi(argv[1]);int ret = 0;sockaddr_in address;bzero(&address, sizeof(address));address.sin_family = AF_INET;if (argc >= 3) {const char *ip =argv[2];inet_pton(AF_INET, ip, &address.sin_addr);}else {address.sin_addr.s_addr = INADDR_ANY;}address.sin_port = htons(port);int listenfd = socket(PF_INET, SOCK_STREAM, 0);assert(listenfd >= 0);ret = bind(listenfd, (sockaddr*)&address, sizeof(address));assert(ret != -1);ret = listen(listenfd, 5);assert(ret != -1);epoll_event events[MAX_EVENT_NUMBER];int epollfd = epoll_create(5);assert(epollfd != -1);addfd(epollfd, listenfd, false);while(1) {int ret = epoll_wait(epollfd, events, MAX_EVENT_NUMBER, -1);if (ret < 0) {printf("epoll failure\n");break;}for (int i=0; i<ret; i++) {int sockfd = events[i].data.fd;if (sockfd == listenfd) {sockaddr_in client_address;socklen_t client_addrlength = sizeof(client_address);int connfd = accept(listenfd, (sockaddr*)&client_address,&client_addrlength);addfd(epollfd, connfd, true);printf("new connection is added to epollfd\n");}else if (events[i].events & EPOLLIN) {pthread_t thread;fds fds_for_new_worker;fds_for_new_worker.epollfd = epollfd;fds_for_new_worker.sockfd = sockfd;// new threadpthread_create(&thread, NULL, worker,(void*)&fds_for_new_worker);}else {printf("something else happened\n");}}}close(listenfd);return 0;}

以下是使用telnet客户端发送的文本，匀速敲入代码：

$telnet 127.0.0.1 12346
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
hi1
hi2
hi3
hi4
hi5
hi6
hi7
hi8
Connection closed by foreign host.

以下是服务器的运行和输出：

$./epoll_oneshot 12346
new connection is added to epollfd
start new thread 1734051584 to recv data on fd: 5
thread 1734051584 get content: hi1thread 1734051584 about to sleep
thread 1734051584 back from sleep
thread 1734051584 get content: hi2
hi3thread 1734051584 about to sleep
thread 1734051584 back from sleep
thread 1734051584 get content: hi4
hi5
hi6thread 1734051584 about to sleep
thread 1734051584 back from sleep
thread 1734051584 get content: hi7thread 1734051584 about to sleep
thread 1734051584 back from sleep
EAGAIN read later
start new thread 1723561728 to recv data on fd: 5
thread 1723561728 get content: hi8thread 1723561728 about to sleep
thread 1723561728 back from sleep
EAGAIN read later
^C