在利用epoll編寫網絡應用程序，特別是服務器的時候。為了得到最優的效果，一般采用邊緣觸發(epoll ET)的方式。由於邊緣觸發，epoll_wait只有在套接字狀態發生變化的時候才會返回。所以要對套接字(socket)進行循環accept，read，write；直到套接字的緩沖區空(read,accept)或者填滿(write)為止。當read返回的字節數小於要讀的字節數，或者返回EAGAIN的時候，認為緩存區為空了。由於網絡上已經有很多epollet如何處理epollin事件的例子，所以下面是本人只提供測試如何處理epollout事件的代碼。
/*
============================================================================
Name : epoll_test.c
Author :
Version :
Copyright : Your copyright notice
Description : epoll et example(echo) 此echo服務器對輸入的內容復制了REPEAT_NUM20000次），然後返回給客戶端
用於測試epollout事件如何觸發。
============================================================================
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <signal.h>
#define EPOLL_SIZE 10
#define EVENT_ARR 20
#define BACK_QUEUE 10
#define PORT 18001
#define BUF_SIZE 16
#define REPEAT_NUM 20000
#define OUT_BUF_SIZE 32*REPEAT_NUM
int g_srv_fd;
//由於有可能不能一次write所有的內容，所以需要全局變量保存內容的長度，內容輸出到那裡，
//在監聽到epollout事件後繼續上一次的發送
char g_out_buf[OUT_BUF_SIZE];//保存輸出的內容
int g_out_buf_offset; //保存輸出到那裡
int g_out_buf_len; //保存輸出內容的長度
int g_has_write_buf; //保存是否要寫輸出內容
void setnonblocking(int sockFd) {
int opt;
opt = fcntl(sockFd, F_GETFL);
if (opt < 0) {
printf("fcntl(F_GETFL) fail.");
exit(-1);
}
opt |= O_NONBLOCK;
if (fcntl(sockFd, F_SETFL, opt) < 0) {
printf("fcntl(F_SETFL) fail.");
exit(-1);
}
}
void handle_sig(int signum) {
close(g_srv_fd);
fprintf(stderr, "receiv sig int");
sleep(5);
exit(0);
}
int write_out_buf(int fd, char *out_buf,int buf_len,int offset)
{
int snd_len = write(fd, out_buf+offset, buf_len-offset);
int tmp_len;
if (snd_len==(buf_len-offset)){
do{
tmp_len = write(fd, out_buf+offset+snd_len, buf_len-offset-snd_len);
if (tmp_len>0 && tmp_len<(buf_len-offset-snd_len)){
snd_len += tmp_len;
break;
}
if(tmp_len == -1){
break;
}
snd_len += tmp_len;
}while(tmp_len>0);
}
if (((snd_len==-1||tmp_len==-1) && errno ==EAGAIN) || snd_len<buf_len-offset){
fprintf(stderr, "snd receiv eagin or snd_len<out_len\r\n");
}
fprintf(stderr, "snd ret:%d\r\n", snd_len);
return snd_len;
}
//
void process_write(int fd, char *in_buf,int buf_len)
{
char *p_out_buf=g_out_buf;
int tmp_offset;
int i;
for(i=0; i<REPEAT_NUM;i++){
tmp_offset+=snprintf(p_out_buf+tmp_offset,OUT_BUF_SIZE-tmp_offset,"%d:%s\r\n", i,in_buf);
}
g_out_buf_len =tmp_offset;
g_out_buf_offset = 0;
g_has_write_buf = 0;
g_out_buf_offset +=write_out_buf(fd, g_out_buf, g_out_buf_len,g_out_buf_offset);
fprintf(stderr, "write_out_buf len:%d wret:%d\r\n", g_out_buf_len, g_out_buf_offset);
if (g_out_buf_offset<g_out_buf_len){
g_has_write_buf=1;
}
}
int main() {
int serverFd;
serverFd = socket(AF_INET, SOCK_STREAM, 0);
g_srv_fd = serverFd;
setnonblocking(serverFd);
signal(SIGPIPE, SIG_IGN);
signal(SIGINT, handle_sig);
int epFd = epoll_create(EPOLL_SIZE);
struct epoll_event ev, evs[EVENT_ARR];
ev.data.fd = serverFd;
ev.events = EPOLLIN | EPOLLET;
epoll_ctl(epFd, EPOLL_CTL_ADD, serverFd, &ev);
struct sockaddr_in serverAddr;
socklen_t serverLen = sizeof(struct sockaddr_in);
serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
serverAddr.sin_port = htons(PORT);
if (bind(serverFd, (struct sockaddr *) &serverAddr, serverLen)) {
printf("bind() fail.\n");
exit(-1);
}
if (listen(serverFd, BACK_QUEUE)) {
printf("Listen fail.\n");
exit(-1);
}
int clientFd;
struct sockaddr_in clientAddr;
socklen_t clientLen;
char buf[BUF_SIZE];
int i = 0;
while (1) {
int nfds = epoll_wait(epFd, evs, EVENT_ARR, -1);
for (i = 0; i < nfds; i++) {
if (evs[i].data.fd == serverFd && (evs[i].events & EPOLLIN)) {
//epollet需要循環對監聽的套接字accept，直到返回EAGAIN
do {
if ((clientFd = accept(serverFd,
(struct sockaddr *) &clientAddr, &clientLen)) < 0) {
printf("accept fail.\n");
break;
}
printf("Connect from %s:%d\n", inet_ntoa(clientAddr.sin_addr),
htons(clientAddr.sin_port));
setnonblocking(clientFd);
ev.data.fd = clientFd;
//注意，為了效率，這裡直接對EPOLLIN，EPOLLOUT事件監聽
ev.events = EPOLLIN | EPOLLET | EPOLLOUT;
//ev.events = EPOLLIN;
epoll_ctl(epFd, EPOLL_CTL_ADD, clientFd, &ev);
}while(clientFd>0);
} else if (evs[i].events & EPOLLIN) {
fprintf(stderr, "epollin event fd:%d\n", clientFd);
if ((clientFd = evs[i].data.fd) > 0) {
//epollet需要對套接字循環的讀，直到len < BUF_SIZE，或者len<=0返回
int len = read(clientFd, buf, BUF_SIZE);
fprintf(stderr, "read fd:%d len:%d\n", clientFd, len);
if (len == BUF_SIZE) {
do {
/*
if (write(clientFd, buf, len) < 0) {
fprintf(stderr, "write fail!\n");
//break;
}
*/
process_write(clientFd, buf, len);
if (len < BUF_SIZE) {
fprintf(stderr, "len <bufsize %d<%d\n", len,
BUF_SIZE);
break;
}
len = read(clientFd, buf, BUF_SIZE);
fprintf(stderr, "read2 fd:%d len:%d\n", clientFd, len);
} while (len > 0);
if (len == 0) {
epoll_ctl(epFd, EPOLL_CTL_DEL, clientFd, &ev);
close(clientFd);
evs[i].data.fd = -1;
fprintf(stderr, "close fd:%d\n", clientFd);
} else if (len == -1 && errno != EAGAIN) {
fprintf(stderr, " fd:%d\n", clientFd);
epoll_ctl(epFd, EPOLL_CTL_DEL, clientFd, &ev);
close(clientFd);
evs[i].data.fd = -1;
}
} else if (len > 0 && len < BUF_SIZE) {
process_write(clientFd, buf, len);
} else if (len == 0 || (len == -1 && errno != EAGAIN)) {
epoll_ctl(epFd, EPOLL_CTL_DEL, clientFd, &ev);
close(clientFd);
evs[i].data.fd = -1;
fprintf(stderr, "close fd:%d\n", clientFd);
}
}
} else if(evs[i].events & EPOLLOUT){
//監聽到epollout時間，說明發送緩沖去可以寫，那繼續上一次的寫操作
clientFd = evs[i].data.fd;
fprintf(stderr, "receive epoll out fd:%d\n", clientFd);
if(g_has_write_buf){
g_out_buf_offset +=write_out_buf(clientFd, g_out_buf, g_out_buf_len,g_out_buf_offset);
fprintf(stderr, "write len :%d writed:%d\n",g_out_buf_len,g_out_buf_offset);
if(g_out_buf_offset==g_out_buf_len){
g_has_write_buf = 0;
}
}
}else {
printf("other event.\n");
}
}
}
return 0;
}
下面是測試的perl代碼epoll_test.pl）
#!/usr/bin/perl
use IO::Socket;
my $host = "127.0.0.1";
my $port = 18001;
my $socket = IO::Socket::INET->new("$host:$port") or die "create socket error $@";
my $msg_out = "1234567890";
print $socket $msg_out;
print "now send over, go to sleep\n";
sleep(10);
my $msg_in;
while (1){
read $socket, $msg_in, 10240;
print "receiv msg $msg_in\n";
}
print "5 second gonesend another line\n";
#print $socket $msg_out;
while (1)
{
sleep(1);
}
運行效果
epollin event fd:5
read fd:5 len:0
close fd:5
Connect from 127.0.0.1:48552
accept fail.
epollin event fd:-1
read fd:5 len:10
snd receiv eagin or snd_len<out_len
snd ret:65536
write_out_buf len:408890 wret:65536
receive epoll out fd:5
snd receiv eagin or snd_len<out_len
snd ret:131072
write len :408890 writed:196608
receive epoll out fd:5
snd receiv eagin or snd_len<out_len
snd ret:65536
write len :408890 writed:262144
receive epoll out fd:5
snd receiv eagin or snd_len<out_len
snd ret:49152
write len :408890 writed:311296
receive epoll out fd:5
snd receiv eagin or snd_len<out_len
snd ret:49152
write len :408890 writed:360448
receive epoll out fd:5
snd ret:48442
write len :408890 writed:408890
epollin event fd:5
read fd:5 len:0
close fd:5
本文出自 “我的it生活-linux|arm” 博客，請務必保留此出處http://herojames.blog.51cto.com/851340/303279
