本文轉(zhuǎn)載自：?http://blog.csdn.net/liuguanghui1988/article/details/7090531
Libevent的應(yīng)用主要圍繞幾大事件：超時(shí)事件、信號(hào)事件、讀/寫事件。
下面就一一簡(jiǎn)單介紹一下它們的使用。
超時(shí)事件
示例：
/*
* Compile with:
* gcc time-test time-test.c -o time-test time-test -I/usr/local/include -L/usr/local/lib -levent
*/
/*
* XXX This sample code was once meant to show how to use the basic Libevent
* interfaces, but it never worked on non-Unix platforms, and some of the
* interfaces have changed since it was first written. It should probably
* be removed or replaced with something better.
*
* Compile with:
* gcc -I/usr/local/include -o time-test time-test.c -L/usr/local/lib -levent
*/
#include
<sys/types.h>
#include
<sys/stat.h>
#include
<time.h>
#ifdef _EVENT_HAVE_SYS_TIME_H
#include
<sys/time.h>
#endif
#include
<stdio.h>
#include
<event2/
event
.h>
#include
<event2/event_struct.h>
#include
<event2/util.h>
struct
timeval lasttime;
int
event_is_persistent;
static
void
timeout_cb(evutil_socket_t fd,
short
event
,
void
*
arg)
{
struct
timeval newtime, difference;
struct
event
*timeout =
arg;
double
elapsed;
evutil_gettimeofday(
&
newtime, NULL);
evutil_timersub(
&newtime, &lasttime, &
difference);
elapsed
= difference.tv_sec +
(difference.tv_usec
/
1.0e6
);
printf(
"
timeout_cb called at %d': %.3f seconds elapsed.\n
"
,
(
int
)newtime.tv_sec, elapsed);
lasttime
=
newtime;
//
/* 啟動(dòng)此測(cè)試程序時(shí),不加-p參數(shù),使用以下代碼也可實(shí)現(xiàn)相同功能 */
//
struct timeval tv;
//
evutil_timerclear(&tv);
//
tv.tv_sec = 1;
//
event_add(timeout, &tv);
//
再次添加定時(shí)事件
}
int
main(
int
argc,
char
**
argv)
{
struct
event
timeout;
//
創(chuàng)建事件
struct
timeval tv;
struct
event_base *
base
;
//
創(chuàng)建事件"總管"的指針
int
flags;
//
事件標(biāo)志,超時(shí)事件可不設(shè)EV_TIMEOUT,因?yàn)樵谔砑邮录r(shí)可設(shè)置
if
(argc ==
2
&& !strcmp(argv[
1
],
"
-p
"
)) {
event_is_persistent
=
1
;
flags
= EV_PERSIST;
//
使得事件具有持久性(否則事件只會(huì)調(diào)度一次)
}
else
{
event_is_persistent
=
0
;
flags
=
0
;
}
/*
Initalize the event library
*/
base
= event_base_new();
//
創(chuàng)建事件"總管"
/*
Initalize one event
*/
event_assign(
&timeout,
base
, -
1
, flags, timeout_cb, (
void
*) &
timeout);
evutil_timerclear(
&
tv);
tv.tv_sec
=
1
;
event_add(
&timeout, &tv);
//
添加事件,同時(shí)設(shè)置超時(shí)時(shí)間
evutil_gettimeofday(&
lasttime, NULL);
event_base_dispatch(
base
);
//
循環(huán)監(jiān)視事件,事件標(biāo)志的條件發(fā)生,就調(diào)用回調(diào)函數(shù)
return
(
0
);
}
?/*******************************************************/
啟動(dòng)進(jìn)程：
[lgh@localhost test]$ ./libe_timer_test -p
結(jié)果：
timeout_cb called at 1325693811': 1.000 seconds elapsed.
timeout_cb called at 1325693812': 1.000 seconds elapsed.
timeout_cb called at 1325693813': 1.001 seconds elapsed.
timeout_cb called at 1325693814': 1.000 seconds elapsed.
timeout_cb called at 1325693815': 1.000 seconds elapsed.
以一行/秒的速率打印以上信息，也就是每秒打印一行。因?yàn)槌瑫r(shí)為一秒。
==============================
啟動(dòng)進(jìn)程：
[lgh@localhost test]$ ./libe_timer_test
結(jié)果：
timeout_cb called at 1325693516: 1.000 seconds elapsed.
沒(méi)有-p參數(shù),事件只調(diào)度一次。如果不加EV_PERSIST標(biāo)志也想實(shí)現(xiàn)事件的持續(xù)性，還有一種辦法，就是在回調(diào)函數(shù)的后面再添加該事件，即上面回調(diào)函數(shù)的批量注釋代碼。
?
信號(hào)事件
示例：
/*
* Compile with:
* gcc libe_signal_test.c -o libe_signal_test -I/usr/local/include -L/usr/local/lib -levent
*/
#include
<signal.h>
#include
<stdio.h>
#include
<
event
.h>
#include
<event2/
event
.h>
#ifdef _EVENT___func__
#define
__func__ _EVENT___func__
#endif
//
int called = 0;
static
void
signal_cb(evutil_socket_t fd,
short
event
,
void
*
arg)
{
struct
event
*signal =
arg;
sleep(
10
);
printf(
"
%s: got signal %d\n
"
, __func__, EVENT_SIGNAL(signal));
//
if (called >= 2)
//
event_del(signal);
//
called++;
}
int
main(
int
argc,
char
**
argv)
{
struct
event
signal_usr;
struct
event_base*
base
;
/*
Initalize the event library
*/
base
=
event_base_new();
/*
Initalize one event
*/
event_assign(
&signal_usr,
base
, SIGUSR1, EV_SIGNAL|
EV_PERSIST, signal_cb,
&
signal_usr);
event_add(
&
signal_usr, NULL);
event_base_dispatch(
base
);
event_base_free(
base
);
printf(
"
end of main!\n
"
);
return
(
0
);
}
啟動(dòng)進(jìn)程：
[lgh@localhost test]$ ./libe_signal_test &
[1] 2998
用kill -10 2998命令給進(jìn)程發(fā)送信號(hào)SIGUSR1，進(jìn)程的的執(zhí)行結(jié)果如下：
[lgh@localhost test]$ kill -10 2998
[lgh@localhost test]$ kill -10 2998
signal_cb: got signal 10
?[lgh@localhost test]$ kill -10 2998
signal_cb: got signal 10
[lgh@localhost test]$ signal_cb: got signal 10
給進(jìn)程發(fā)送了3次SIGUSR1信號(hào)，信號(hào)回調(diào)函數(shù)執(zhí)行了三次（其中最后一行隔了幾秒才打印出來(lái)）。這說(shuō)明libevent對(duì)linux中的不可靠信號(hào)也是支持排隊(duì)的。
?
讀/寫事件
文件描述符是否可讀/寫，這個(gè)不太好模擬（可能用文件的讀/寫鎖可以實(shí)現(xiàn)模擬，鄙人目前還沒(méi)有嘗試過(guò)，有試過(guò)的朋友可以指點(diǎn)一下），有一種方法就是用socket連接來(lái)模擬，先建立一個(gè)服務(wù)端和客戶端，當(dāng)服務(wù)端的監(jiān)聽端口可讀時(shí)說(shuō)明有一個(gè)新的連接請(qǐng)求。
示例：
?服務(wù)端——proc_server.c
#include <sys/socket.h>
#include
<sys/types.h>
#include
<netinet/
in
.h>
#include
<stdio.h>
#include
<
event
.h>
#include
<event2/
event
.h>
#include
<errno.h>
#define
PORT 6666
//
----------需改靈活點(diǎn)
#define
BACKLOG 10
//
好像沒(méi)起到作用，我設(shè)置為1，在同一機(jī)子下開兩個(gè)連接，沒(méi)彈出警告信息
#define
EV_BUFSIZE_T sizeof(pid_t)
//
服務(wù)端與客戶端傳遞數(shù)據(jù)的buffer大小
/*
管理每一個(gè)連接的讀寫事件和數(shù)據(jù)
*/
typedef
struct
sock_event {
struct
event
*read_ev;
//
讀事件
struct
event
*write_ev;
//
寫事件
pid_t *buffer;
//
buffer僅存進(jìn)程pid
int
gapbeats;
//
定時(shí)間隔
int
maxbeats;
//
在客戶端不工作或退出的情況下，服務(wù)端的最大檢測(cè)次數(shù)
int
pastbeats;
//
沒(méi)有收到數(shù)據(jù)的情況下，當(dāng)前的心跳檢測(cè)數(shù)
}sock_ev;
struct
event_base*
base
;
//
管理所有連接事件
/*
釋放堆分配的sock_ev結(jié)構(gòu)體
*/
void
release_sock_ev(sock_ev *
ev)
{
event_del(ev
->
read_ev);
free(ev
->
read_ev);
event_del(ev
->
write_ev);
free(ev
->
write_ev);
free(ev
->
buffer);
free(ev);
}
/*
功能:創(chuàng)建一個(gè)sock_ev結(jié)構(gòu)體,并且將它初始化.
* 參數(shù):gapbeats,服務(wù)端兩個(gè)檢測(cè)心跳的間隔時(shí)間(單位:秒);
* maxbeats,沒(méi)有收到客戶端數(shù)據(jù)的最大檢測(cè)次數(shù).
* 返回:sock_ev結(jié)構(gòu)體指針.
*/
sock_ev
* create_sock_ev(
int
gapbeats,
int
maxbeats)
{
sock_ev
* se = (sock_ev *)malloc(
sizeof
(sock_ev));
if
(!
se)
return
NULL;
memset(se,
0
,
sizeof
(sock_ev));
se
->read_ev = (
struct
event
*)malloc(
sizeof
(
struct
event
));
se
->write_ev = (
struct
event
*)malloc(
sizeof
(
struct
event
));
se
->buffer = (pid_t *
)malloc(EV_BUFSIZE_T);
if
(!se->read_ev || !se->write_ev || !se->
buffer)
return
NULL;
memset(se
->read_ev,
0
,
sizeof
(
struct
event
));
memset(se
->write_ev,
0
,
sizeof
(
struct
event
));
memset(se
->buffer,
0
, EV_BUFSIZE_T);
se
->gapbeats =
gapbeats;
se
->maxbeats =
maxbeats;
se
->pastbeats =
0
;
return
se;
}
/*
功能:寫事件回調(diào)函數(shù)
* 參數(shù):libevent回調(diào)函數(shù)的三個(gè)典型參數(shù)
* sock,文件描述符;event,事件類型(EV_WRITE);arg,傳給函數(shù)的數(shù)據(jù)指針(buffer)
* 返回: void (libevent回調(diào)函數(shù)的返回為void)
*/
void
socket_write(
int
sock,
short
event
,
void
*
arg)
{
pid_t
*
buffer;
if
(!
arg)
return
;
buffer
= (pid_t*
)arg;
if
(send(sock, buffer,
sizeof
(*buffer),
0
) <
0
) {
printf(
"
server send msg error: errno %d--%s\n
"
, errno, strerror(errno));
return
;
}
memset(buffer,
0
,
sizeof
(*
buffer));
}
/*
功能:讀事件回調(diào)函數(shù)
* 參數(shù):libevent回調(diào)函數(shù)的三個(gè)典型參數(shù)
* sock,文件描述符;event,事件類型(EV_READ);arg,傳給函數(shù)的數(shù)據(jù)指針(sock_ev)
* 返回: void.
*/
void
socket_read(
int
sock,
short
event
,
void
*
arg)
{
int
size;
sock_ev
* sockev = (sock_ev*
)arg;
if
(!
sockev)
return
;
memset(sockev
->buffer,
0
, EV_BUFSIZE_T);
size
= recv(sock, sockev->buffer, EV_BUFSIZE_T,
0
);
if
(size <=
0
) {
//
接收數(shù)據(jù)失敗
sockev->pastbeats++;
//
全局變量
printf(
"
pastbeats:\t%d\n
"
, sockev->pastbeats);
//
--debug
if
(sockev->pastbeats >= sockev->
maxbeats) {
printf(
"
---client error or exit:please restart\n
"
);
//
--debug
release_sock_ev(sockev);
close(sock);
}
return
;
}
sockev
->pastbeats =
0
;
printf(
"
pastbeats:\t%d\n
"
, sockev->pastbeats);
//
--debug
printf(
"
receive data:\t%d size:\t%d\n
"
, *sockev->
buffer, size);
event_add(sockev
->write_ev, NULL);
//
添加端口寫事件，將數(shù)據(jù)返回給客戶端
}
/*
功能:接受新連接請(qǐng)求
* 參數(shù):libevent回調(diào)函數(shù)的三個(gè)典型參數(shù)
* sock,文件描述符;event,事件類型(EV_READ,監(jiān)聽端口可讀,表示有新連接請(qǐng)求);
arg,目前為空指針.
* 返回: void.
*/
void
connect_accept(
int
sock,
short
event
,
void
*
arg)
{
struct
sockaddr_in cli_addr;
int
connetfd, sin_size;
struct
timeval beat;
//
定時(shí)讀事件,來(lái)檢測(cè)客戶端發(fā)送了數(shù)據(jù)
sock_ev* sockev;
//
為連接建立端口事件
if
((sockev = create_sock_ev(
1
,
10
)) ==
NULL)
return
;
sin_size
=
sizeof
(
struct
sockaddr_in);
connetfd
= accept(sock, (
struct
sockaddr*)&cli_addr, &
sin_size);
if
(connetfd == -
1
) {
printf(
"
server accept() error: errno %d--%s\n
"
, errno, strerror(errno));
return
;
}
event_assign(sockev
->read_ev,
base
, connetfd, EV_PERSIST, socket_read, sockev);
//
下面是老版接口
//
event_set(sockev->read_ev, connetfd, EV_PERSIST, socket_read, sockev);
//
讀事件 (若加上EV_READ|,則定時(shí)讀會(huì)失效)
//
event_base_set(base, sockev->read_ev);
evutil_timerclear(&
beat);
beat.tv_sec
= sockev->gapbeats;
//
定期檢查端口是否可讀,來(lái)判斷客戶端是否存在
event_add(sockev->read_ev, &
beat);
event_assign(sockev
->write_ev,
base
, connetfd, EV_WRITE, socket_write, sockev->buffer);
//
寫事件
//
event_set(sockev->write_ev, connetfd, EV_WRITE, socket_write, sockev->buffer);
//
event_base_set(base, sockev->write_ev);
}
int
main(
int
argc,
char
*
argv[])
{
struct
sockaddr_in server_addr;
int
sock;
//
struct event listen_ev;
//
創(chuàng)建連接請(qǐng)求監(jiān)聽事件
struct
event
*
listen_ev;
sock
= socket(AF_INET, SOCK_STREAM,
0
);
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (
int
*)
1
,
sizeof
(
int
));
memset(
&server_addr,
0
,
sizeof
(server_addr));
server_addr.sin_family
=
AF_INET;
server_addr.sin_port
=
htons(PORT);
server_addr.sin_addr.s_addr
=
INADDR_ANY;
if
(bind(sock, (
struct
sockaddr*)&server_addr,
sizeof
(
struct
sockaddr)) == -
1
) {
printf(
"
bind socket error: errno %d--%s\n
"
, errno, strerror(errno));
exit(
0
);
}
if
(listen(sock, BACKLOG) == -
1
) {
printf(
"
listen socket error: errno %d--%s\n
"
, errno, strerror(errno));
exit(
0
);
}
base
= event_base_new();
//
base,全局變量.
listen_ev = event_new(
base
, sock, EV_READ|EV_PERSIST, connect_accept, NULL);
//
創(chuàng)建evnet對(duì)象并初始化
if
(!
listen_ev) {
printf(
"
event_new() fail\n
"
);
exit(
0
);
}
//
event_set(&listen_ev, sock, EV_READ|EV_PERSIST, connect_accept, NULL); 這是老接口
//
event_base_set(base, &listen_ev);
event_add(listen_ev, NULL);
//
添加到監(jiān)視事件集中，event就變成的未決狀態(tài)
event_base_dispatch(
base
);
//
輪詢監(jiān)視所有事件
if
(event_del(listen_ev) ==
0
) {
//
從監(jiān)視事件集中刪除
event_free(listen_ev);
//
刪除事件,釋放空間
}
event_base_free(
base
);
//
刪除base對(duì)象
exit(
0
);
}
客戶端：proc_client.c
#include<stdio.h>
#include
<stdlib.h>
#include
<
string
.h>
#include
<errno.h>
#include
<sys/types.h>
#include
<sys/socket.h>
#include
<netinet/
in
.h>
#include
<
event
.h>
#include
<event2/
event
.h>
#include
<event2/util.h>
#define
MAXLINE 1024
static
void
heartbit_cb(evutil_socket_t fd,
short
event
,
void
*
arg);
int
main(
int
argc,
char
**
argv)
{
int
sockfd, n, received;
int
len, bytes;
char
recvline[MAXLINE], sendline[MAXLINE];
pid_t tests
=
getpid();
pid_t
*pids = &
tests;
pid_t testr
=
0
;
pid_t
*pidr = &
testr;
struct
sockaddr_in servaddr;
struct
timeval tv;
struct
event_base*
base
;
struct
event
*
client_ev;
if
( argc !=
2
){
printf(
"
usage: ./client <ip address>\n
"
);
exit(
0
);
}
memset(sendline,
0
, MAXLINE);
if
( (sockfd = socket(AF_INET, SOCK_STREAM,
0
)) <
0
){
printf(
"
create socket error: %s(errno: %d)\n
"
, strerror(errno),errno);
exit(
0
);
}
memset(
&servaddr,
0
,
sizeof
(servaddr));
servaddr.sin_family
=
AF_INET;
servaddr.sin_port
= htons(
6666
);
//
把16位值從主機(jī)字節(jié)序轉(zhuǎn)換成網(wǎng)絡(luò)字節(jié)序
if
( inet_pton(AF_INET, argv[
1
], &servaddr.sin_addr) <=
0
){
//
[將“點(diǎn)分十進(jìn)制”ip－> 網(wǎng)絡(luò)字節(jié)序“整數(shù)”ip]
printf(
"
inet_pton error for %s\n
"
,argv[
1
]);
exit(
0
);
}
if
( connect(sockfd, (
struct
sockaddr*)&servaddr,
sizeof
(servaddr)) <
0
){
printf(
"
connect error: %s(errno: %d)\n
"
,strerror(errno),errno);
exit(
0
);
}
printf(
"
send msg to server: \n
"
);
evutil_timerclear(
&
tv);
tv.tv_sec
=
2
;
base
=
event_base_new();
client_ev
= event_new(
base
, sockfd, EV_PERSIST, heartbit_cb, pids);
if
(!
client_ev) {
printf(
"
event_new() fail\n
"
);
exit(
0
);
}
//
event_set(&client_ev, sockfd, EV_PERSIST, heartbit_cb, pids);
//
若加上EV_WRITE|,sockfd可寫,則會(huì)一直寫(與定時(shí)事件是關(guān)系或) EV_PERSIST
//
event_base_set(base, &client_ev);
event_add(client_ev, &
tv);
event_base_dispatch(
base
);
if
(event_del(client_ev) ==
0
) {
event_free(client_ev);
}
event_base_free(
base
);
close(sockfd);
exit(
0
);
}
/*
功能: 向服務(wù)端發(fā)送心跳包
* 參數(shù):
*
*/
static
void
heartbit_cb(evutil_socket_t fd,
short
event
,
void
*
arg)
{
pid_t
*pid = (pid_t *
)arg;
pid_t testr
=
0
;
pid_t
*pid_recv = &
testr;
int
len;
len
=
sizeof
(pid_t);
if
( send(fd, pid, len,
0
) !=
len) {
printf(
"
send msg error: %s(errno: %d)\n
"
, strerror(errno), errno);
exit(
0
);
}
//
接收從服務(wù)端的返回?cái)?shù)據(jù)
fputs(
"
echo from server:\n
"
, stdout);
if
(recv(fd, pid_recv, len,
0
) <
0
) {
printf(
"
Failed to receive bytes from client\n
"
);
exit(
-
1
);
}
printf(
"
%d\n
"
, *
pid_recv);
fputs(
"
\n
"
, stdout);
}
結(jié)果：
[lgh@localhost proc]$ ./proc_client 192.168.1.107
send msg to server:
echo from server:
7482
echo from server:
7482
echo from server:
7482
--------------------------------------------------------------------------------------------
[lgh@localhost proc]$ ./proc_server
pastbeats: 0
receive data:7482?????? size:4
pastbeats: 0
receive data:7482?????? size:4
pastbeats: 0
receive data:7482?????? size:4
pastbeats: 1
pastbeats: 2
pastbeats: 3
pastbeats: 4
pastbeats: 5
pastbeats: 6
pastbeats: 7
pastbeats: 8
pastbeats: 9
pastbeats: 10
---pastbeats > maxbeats
=============================================================
測(cè)試設(shè)置：客戶端每2秒發(fā)一次心跳,服務(wù)端每1秒去查看端口是否可讀.?
??????????????????? 服務(wù)端若經(jīng)過(guò)10次還沒(méi)收到心跳,則認(rèn)為客戶端已退出.
?測(cè)試過(guò)程：先讓客戶端發(fā)3次心跳,再終止掉客戶端.---用時(shí)6秒。
? ??????????????? ??此時(shí)，服務(wù)端已經(jīng)對(duì)端口發(fā)起了6次檢測(cè)，有3次接收到了數(shù)據(jù)，有3次沒(méi)有收到數(shù)據(jù)。
? ?????????????????? 當(dāng)終止掉客戶端后，服務(wù)端每次檢測(cè)都會(huì)收不到數(shù)據(jù)，現(xiàn)象是：前3次是連續(xù)執(zhí)行了超時(shí)回調(diào)函數(shù)socket_read，這3次沒(méi)有經(jīng)過(guò)每隔1秒執(zhí)行。
? ?????????????????? 后面再每秒檢測(cè)7次，即每秒執(zhí)行一次回調(diào)函數(shù)。總計(jì)10次沒(méi)有收到來(lái)自客戶端的數(shù)據(jù)，判斷客戶端已退出。
?
? 測(cè)試結(jié)果判斷: libevent對(duì)定時(shí)事件支持排隊(duì),即有多少次定時(shí),它就執(zhí)行回調(diào)函數(shù)多少次.
? 編程建議：服務(wù)端的心跳頻率要小于等于客戶端的心跳頻率.（小于，會(huì)有丟包現(xiàn)象，但我們的需求只是檢測(cè)客戶端是否存在）
?
小結(jié)：這個(gè)小例子用來(lái)做進(jìn)程管理，客戶端是不行的，因?yàn)檫@里的客戶端也是libevent的超時(shí)事件，它在輪詢超時(shí)事件的時(shí)候會(huì)一直占用進(jìn)程的cpu，所以這樣是不行的，所以客戶端的定時(shí)發(fā)送心跳包應(yīng)該改用信號(hào)做成一個(gè)小模塊加入到客戶端進(jìn)程中。
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