apache2 - Tornado 是 "a relatively simple, non-blocking web server framework written in Python"-- 可以稍微解释一下这是什么意思吗？

Question

这可能是一个愚蠢的问题，但究竟什么是“非阻塞 Web 服务器”？所有的 Web 服务器在技术上都是非阻塞的，不是吗？否则他们如何处理同时连接？ Apache2 使用 fork() 和 pthreads 的组合来实现这一点。 Tornado(和 Twisted)到底有什么不同？他们是否只是将一堆套接字设置为非阻塞模式，构建一个 FD 列表(或等效的)，然后用一个大的 select() 系统调用循环它？

你会在哪里使用这样的框架，与 Apache2(或其他流行的服务器)相比，它们能给你带来什么优势？谢谢

Answer 1

这个article on EventMachine也可能给你一个提示:

Steeped in the tradition of forking / threaded web-servers I found myself rather surprised when I joined one of the research projects at University of Waterloo a couple of years back: we were benchmarking different web-server architectures, and top performers were all event-driven servers.

As I pestered everyone with questions, I quickly realized why - in an environment with hundreds of thousands requests a second, forking and context switching associated with thread management become prohibitively expensive (fork is worst performer, as it does a memory copy on the parent process every time). Whereas by comparison, a tight and highly optimized event-loop really shines when it comes to performance under heavy loads.