*:first-child {
margin-top: 0 !important;
}
body>*:last-child {
margin-bottom: 0 !important;
}
/* BLOCKS
=============================================================================*/
p, blockquote, ul, ol, dl, table, pre {
margin: 15px 0;
}
/* HEADERS
=============================================================================*/
h1, h2, h3, h4, h5, h6 {
margin: 20px 0 10px;
padding: 0;
font-weight: bold;
-webkit-font-smoothing: antialiased;
}
h1 tt, h1 code, h2 tt, h2 code, h3 tt, h3 code, h4 tt, h4 code, h5 tt, h5 code, h6 tt, h6 code {
font-size: inherit;
}
h1 {
font-size: 28px;
color: #000;
}
h2 {
font-size: 24px;
border-bottom: 1px solid #ccc;
color: #000;
}
h3 {
font-size: 18px;
}
h4 {
font-size: 16px;
}
h5 {
font-size: 14px;
}
h6 {
color: #777;
font-size: 14px;
}
body>h2:first-child, body>h1:first-child, body>h1:first-child+h2, body>h3:first-child, body>h4:first-child, body>h5:first-child, body>h6:first-child {
margin-top: 0;
padding-top: 0;
}
a:first-child h1, a:first-child h2, a:first-child h3, a:first-child h4, a:first-child h5, a:first-child h6 {
margin-top: 0;
padding-top: 0;
}
h1+p, h2+p, h3+p, h4+p, h5+p, h6+p {
margin-top: 10px;
}
/* LINKS
=============================================================================*/
a {
color: #4183C4;
text-decoration: none;
}
a:hover {
text-decoration: underline;
}
/* LISTS
=============================================================================*/
ul, ol {
padding-left: 30px;
}
ul li > :first-child,
ol li > :first-child,
ul li ul:first-of-type,
ol li ol:first-of-type,
ul li ol:first-of-type,
ol li ul:first-of-type {
margin-top: 0px;
}
ul ul, ul ol, ol ol, ol ul {
margin-bottom: 0;
}
dl {
padding: 0;
}
dl dt {
font-size: 14px;
font-weight: bold;
font-style: italic;
padding: 0;
margin: 15px 0 5px;
}
dl dt:first-child {
padding: 0;
}
dl dt>:first-child {
margin-top: 0px;
}
dl dt>:last-child {
margin-bottom: 0px;
}
dl dd {
margin: 0 0 15px;
padding: 0 15px;
}
dl dd>:first-child {
margin-top: 0px;
}
dl dd>:last-child {
margin-bottom: 0px;
}
/* CODE
=============================================================================*/
pre, code, tt {
font-size: 12px;
font-family: Consolas, "Liberation Mono", Courier, monospace;
}
code, tt {
margin: 0 0px;
padding: 0px 0px;
white-space: nowrap;
border: 1px solid #eaeaea;
background-color: #f8f8f8;
border-radius: 3px;
}
pre>code {
margin: 0;
padding: 0;
white-space: pre;
border: none;
background: transparent;
}
pre {
background-color: #f8f8f8;
border: 1px solid #ccc;
font-size: 13px;
line-height: 19px;
overflow: auto;
padding: 6px 10px;
border-radius: 3px;
}
pre code, pre tt {
background-color: transparent;
border: none;
}
kbd {
-moz-border-bottom-colors: none;
-moz-border-left-colors: none;
-moz-border-right-colors: none;
-moz-border-top-colors: none;
background-color: #DDDDDD;
background-image: linear-gradient(#F1F1F1, #DDDDDD);
background-repeat: repeat-x;
border-color: #DDDDDD #CCCCCC #CCCCCC #DDDDDD;
border-image: none;
border-radius: 2px 2px 2px 2px;
border-style: solid;
border-width: 1px;
font-family: "Helvetica Neue",Helvetica,Arial,sans-serif;
line-height: 10px;
padding: 1px 4px;
}
/* QUOTES
=============================================================================*/
blockquote {
border-left: 4px solid #DDD;
padding: 0 15px;
color: #777;
}
blockquote>:first-child {
margin-top: 0px;
}
blockquote>:last-child {
margin-bottom: 0px;
}
/* HORIZONTAL RULES
=============================================================================*/
hr {
clear: both;
margin: 15px 0;
height: 0px;
overflow: hidden;
border: none;
background: transparent;
border-bottom: 4px solid #ddd;
padding: 0;
}
/* TABLES
=============================================================================*/
table th {
font-weight: bold;
}
table th, table td {
border: 1px solid #ccc;
padding: 6px 13px;
}
table tr {
border-top: 1px solid #ccc;
background-color: #fff;
}
table tr:nth-child(2n) {
background-color: #f8f8f8;
}
/* IMAGES
=============================================================================*/
img {
max-width: 100%
}
-->
Nginx惊群问题
“惊群”概念
所谓惊群,可以用一个简单的比喻来说明:
一群等待食物的鸽子,当饲养员扔下一粒谷物时,所有鸽子都会去争抢,但只有少数的鸽子能够抢到食物,
大部分鸽子都是落空的,只能等待饲养员下一次的喂食。
对于Nginx Web Server,就是多个进程都在等待
接受TCP连接请求,一旦TCP连接请求到来,只有一个或者少部分(多个TCP连接请求)进程能够获取连接成
功,而大部分进程在被操作系统唤醒后,获取连接失败,只能再次进入等待。
“惊群”处理
下面采用伪代码描述Nginx在Linux系统下对于“惊群”问题的处理
while (true) {
if (multi-processes) {
/*
* 尝试获取进程共享锁,不管是否成功,都立即返回。
* 如果获取成功,则通过epoll_ctl系统调用把连接等待fd添加到当前进程的epoll监听列表中;
* 如果获取失败,则通过epoll_ctl系统调用把连接等待fd从当前进程的epoll监听列表中移除。
*/
if (trylock(进程共享锁)) {
falg |= 接受TCP连接请求;
}
//调整epoll超时等待时间
//...
}
/*
* epoll系统调用:
* 1.获取TCP连接请求fd,加入TCP连接请求队列;
* 2.获取TCP数据接收,发送请求fd,加入数据处理队列。
*/
process_epoll_event();
if (新的TCP连接请求) {
对TCP连接等待fd多次执行接受TCP连接请求处理(accept or accept4);
}
if (进程共享锁) {
释放进程共享锁;
}
//处理数据接收,发送请求队列
//...
}