无阻塞Web服务器如何工作? [英] How non-blocking web server works?

问题描述

我正在尝试理解非阻塞式Web服务器的想法，似乎我想念一些东西.

I'm trying to understand the idea of non-blocking web server and it seems like there is something I miss.

我了解阻止"网络请求(伪代码)的原因有以下几种:

I can understand there are several reasons for "block" web request(psuedocode):

1. CPU绑定

1. CPU bound

字符串on_request(arg)
{
DO_SOME_HEAVY_CPU_CALC
返回完成"；
}

string on_request(arg)
{
DO_SOME_HEAVY_CPU_CALC
return "done";
}

IO绑定

字符串on_request(arg)
{
DO_A_CALL_TO_EXTERNAL_RESOURCE_SUCH_AS_WEB_IO
返回完成"；
}

string on_request(arg)
{
DO_A_CALL_TO_EXTERNAL_RESOURCE_SUCH_AS_WEB_IO
return "done";
}

睡觉

字符串on_request(arg)
{
睡眠(VERY_VERY_LONG_TIME);
返回完成"；
}

string on_request(arg)
{
sleep(VERY_VERY_LONG_TIME);
return "done";
}

• 这三者都能从非阻塞服务器中受益吗?
• 从无阻塞Web服务器中真正受益的情况是如何做到的? 我的意思是，当查看Tornado服务器文档时，似乎 喜欢它释放"线程.我知道线程可以入睡 并等待来自操作系统的信号(至少在Linux中)， 这是释放"线程的意思吗?这高一些吗 级别的实施?实际上创建新线程的东西 正在等待新请求，而不是正在睡觉"的请求?
• 我在这里想念东西吗?

• are all the three can benefit from non-blocking server?
• how the situation that do benefit from the non-blocking web server really do that? I mean, when looking at the Tornado server documentation, it seems like it "free" the thread. I know that a thread can be put to sleep and wait for a signal from the operation system (at least in Linux), is this the meaning of "freeing" the thread? is this some higher level implementation? something that actually create a new thread that is waiting for new request instead of the "sleeping" one?
• Am I missing something here?

谢谢

推荐答案

基本上，无阻塞套接字I/O的工作方式是使用轮询和状态机.因此，您的许多连接方案都是这样的:

Basically the way the non-blocking sockets I/O work is by using polling and the state machine. So your scheme for many connections would be something like that:

• 创建许多套接字并使它们无阻塞
• 将它们的状态切换为连接"
• 对它们每个启动connect操作
• 对所有对象进行轮询，直到发生某些事件为止
• 处理激发的事件(连接建立或连接失败)
• 将已建立的状态切换为发送"
• 在缓冲区中准备Web请求
• 轮询发送"套接字以进行WRITE操作
• send获得WRITE事件集的人的数据
• 对于已发送所有数据的用户，将状态切换为正在接收"
• 轮询接收"套接字以进行READ操作
• 对于设置了READ事件的用户，请执行read并根据协议处理读取的数据
• 如果协议是双向的，请重复；如果不是双向的，请关闭套接字.

• Create many sockets and make them nonblocking
• Switch the state of them to "connect"
• Initiate the connect operation on each of them
• Poll all of them until some events fire up
• Process the fired up events (connection established or connection failed)
• Switch the state those established to "sending"
• Prepare the Web request in a buffer
• Poll "sending" sockets for WRITE operation
• send the data for those who got the WRITE event set
• For those which have all the data sent, switch the state to "receiving"
• Poll "receiving" sockets for READ operation
• For those which have the READ event set, perform read and process the read data according to the protocol
• Repeat if the protocol is bidirectional, or close the socket if it is not

当然，在每个阶段，您都需要处理错误，并且每个套接字的状态都不同(一个可能正在连接，而另一个可能已经在读取).

Of course, at each stage you need to handle errors, and that the state of each socket is different (one may be connecting while another may be already reading).

关于轮询，我在这里发布了有关不同轮询方法如何工作的文章:

Regarding polling I have posted an article about how different polling methods work here: http://www.ulduzsoft.com/2014/01/select-poll-epoll-practical-difference-for-system-architects/ - I suggest you check it.

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