libevent是一个用C语言编写的、轻量级的开源高性能事件通知库，由 Niels Provos 和 Nick Mathewson 开发。它提供了一种机制来执行事件通知，允许程序在单个线程中高效地处理多个事件源，包括IO事件、定时事件和信号事件，使得开发者能够构建出响应迅速且易于扩展的网络应用程序。特别是在需要处理大量并发连接的场景中。它支持多种平台，包括Linux、Unix和Windows，并且提供了跨平台的事件处理机制。
Github： https://github.com/libevent/libevent
select、poll、epoll、kqueue、dev/poll 等多种 I/O 多路复用技术，可以根据不同的操作系统和需求选择合适的机制。libevent 的安装和编译相对简单，可以通过源码编译或使用包管理器（如： apt-get 、 yum 等）进行安装。对于源码编译，通常需要先下载 Libevent 的源码包，然后解压、配置、编译和安装。
查看是否已经安装
ls -al /usr/lib | grep libevent
下载 libevent-2.1.12-stable.tar.gz
wget https://github.com/libevent/libevent/releases/download/release-2.1.12-stable/libevent-2.1.12-stable.tar.gz
解压 libevent
tar -zxvf libevent-2.1.12-stable.tar.gz
配置安装目录
./configure --prefix=/usr/local/libevent-2.1.12
编译安装
make && make install
如果在
libevent安装目录make之后会生成一个.libs/， 里面如果没有libevent\_openssl.so说明系统没有安装openssl库。但是如果安装了，依然没有这个文件生成，可能需要制定openssl路径。
ln -s /usr/local/ssl/include/openssl /usr/include/openssl
查看是否安装成功
$ ls -al /usr/local/ | grep libevent
drwxr-xr-x 5 root root 4096 Mar 17 2024 libevent-2.1.12
在 sample 目录下会有已经编译好的服务器应用程序。
cd libevent-2.1.12-stable/sample
可以拿 hello-world 程序用来测试。
ls
dns-example hello-world http-connect.c https_client-openssl_hostname_validation.o le-proxy.c signal-test.o
dns-example.c hello-world.c http-connect.o http-server le_proxy-le-proxy.o time-test
dns-example.o hello-world.o https-client http-server.c openssl_hostname_validation.c time-test.c
event-read-fifo hostcheck.c https-client.c http-server.o openssl_hostname_validation.h time-test.o
event-read-fifo.c hostcheck.h https_client-hostcheck.o include.am signal-test
event-read-fifo.o http-connect https_client-https-client.o le-proxy signal-test.c
服务端
./hello-world
# 客户端连接响应如下
flushed answer
客户端
netcat 172.30.237.24 9995
Hello, World!
如果客户端收到 Hello, World! 字符串，表示 libevent 在本机可以正常使用。
当使用 ./http-server 命令来启动一个 HTTP 服务器。对于 http-server ，你可以使用 -p 或 --port 参数来指定端口号。最后一个参数为服务器根目录。
具体的命令格式：
./http-server -p 8886 /home/www/build/libevent-2.1.12-stable/sample/
8886/home/www/build/libevent-2.1.12-stable/sample/这两个命令都会启动 http-server ，并让它监听在 8686 端口上。你可以通过浏览器访问 http://localhost:8686 来查看服务器上的内容。
在根目录： /home/www/build/libevent-2.1.12-stable/sample/ 新建一个静态测试文件 tinywan.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Tinywan(ShaoBo Wan)</title>
</head>
<body>
<h1>开源技术小栈</h1>
</body>
</html>
服务端
./http-server -p 8886 /home/www/build/libevent-2.1.12-stable/sample/
Listening on 0.0.0.0:8886
Got a GET request for </tinywan.html>
Got a GET request for </tinywan.html>
客户端
curl -i http://172.30.237.24:8886/tinywan.html
HTTP/1.1 200 OK
Content-Type: text/html
Date: Thu, 08 Aug 2024 02:12:53 GMT
Content-Length: 165
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Tinywan(ShaoBo Wan)</title>
</head>
<body>
<h1>开源技术小栈</h1>
</body>
</html>
访问首页
HTTP/1.1 200 OK
Content-Type: text/html
Date: Thu, 08 Aug 2024 02:16:21 GMT
Content-Length: 2206
<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<title>/</title>
<base href='/'>
</head>
<body>
<h1>/</h1>
<ul>
<li><a href="time-test.o">time-test.o</a>
<li><a href="hello-world">hello-world</a>
<li><a href="http-connect.c">http-connect.c</a>
<li><a href=".deps">.deps</a>
<li><a href="openssl_hostname_validation.c">openssl_hostname_validation.c</a>
<li><a href=".libs">.libs</a>
<li><a href="http-connect">http-connect</a>
<li><a href="hostcheck.c">hostcheck.c</a>
<li><a href="dns-example.o">dns-example.o</a>
<li><a href="signal-test.o">signal-test.o</a>
<li><a href=".">.</a>
<li><a href="http-server.c">http-server.c</a>
<li><a href="time-test.c">time-test.c</a>
<li><a href="signal-test">signal-test</a>
<li><a href="http-connect.o">http-connect.o</a>
<li><a href="https_client-hostcheck.o">https_client-hostcheck.o</a>
<li><a href="signal-test.c">signal-test.c</a>
<li><a href=".dirstamp">.dirstamp</a>
<li><a href="openssl_hostname_validation.h">openssl_hostname_validation.h</a>
<li><a href="..">..</a>
<li><a href="https_client-openssl_hostname_validation.o">https_client-openssl_hostname_validation.o</a>
<li><a href="event-read-fifo.c">event-read-fifo.c</a>
<li><a href="http-server.o">http-server.o</a>
<li><a href="le-proxy.c">le-proxy.c</a>
<li><a href="http-server">http-server</a>
<li><a href="event-read-fifo.o">event-read-fifo.o</a>
<li><a href="include.am">include.am</a>
<li><a href="https_client-https-client.o">https_client-https-client.o</a>
<li><a href="le_proxy-le-proxy.o">le_proxy-le-proxy.o</a>
<li><a href="hello-world.c">hello-world.c</a>
<li><a href="tinywan.html">tinywan.html</a>
<li><a href="le-proxy">le-proxy</a>
<li><a href="hostcheck.h">hostcheck.h</a>
<li><a href="time-test">time-test</a>
<li><a href="https-client">https-client</a>
<li><a href="dns-example.c">dns-example.c</a>
<li><a href="dns-example">dns-example</a>
<li><a href="https-client.c">https-client.c</a>
<li><a href="event-read-fifo">event-read-fifo</a>
<li><a href="hello-world.o">hello-world.o</a>
</ul></body></html>
~/build/libevent-2.1.12-stable/sample$ ./time-test
timeout_cb called at 1723083770: 2.002 seconds elapsed.
timeout_cb called at 1723083772: 2.002 seconds elapsed.
timeout_cb called at 1723083774: 2.002 seconds elapsed.
timeout_cb called at 1723083776: 2.002 seconds elapsed.
timeout_cb called at 1723083778: 2.002 seconds elapsed.
timeout_cb called at 1723083780: 2.002 seconds elapsed.
timeout_cb called at 1723083782: 2.002 seconds elapsed.
timeout_cb called at 1723083784: 2.002 seconds elapsed.
timeout_cb called at 1723083786: 2.002 seconds elapsed.
timeout_cb called at 1723083788: 2.002 seconds elapsed.
timeout_cb called at 1723083790: 2.001 seconds elapsed.
timeout_cb called at 1723083792: 2.002 seconds elapsed.
timeout_cb called at 1723083794: 2.002 seconds elapsed.
总的来说，Libevent以其高性能、轻量级、跨平台和丰富的API等特性，在网络编程中发挥着重要作用，特别是在需要处理大量并发连接的应用场景中。