Python并发编程eventlet

r囧r小猫 2022-06-17 04:12 206阅读 0赞

# 1 多进程、多线程和协程 #

python并发编程之多进程、多线程、异步和协程：http://www.cnblogs.com/tyomcat/p/5486827.html

## 1.1 总结 ##

1）多进程能够利用多核优势，但是进程间通信比较麻烦，另外，进程数目的增加会使性能下降，进程切换的成本较高。程序流程复杂度相对I/O多路复用要低。  
2）I/O多路复用是在一个进程内部处理多个逻辑流程，不用进行进程切换，性能较高，另外流程间共享信息简单。但是无法利用多核优势，另外，程序流程被事件处理切割成一个个小块，程序比较复杂，难于理解。  
3）线程运行在一个进程内部，由操作系统调度，切换成本较低，另外，他们共享进程的虚拟地址空间，线程间共享信息简单。但是线程安全问题导致线程学习曲线陡峭，而且易出错。  
4）协程有编程语言提供，由程序员控制进行切换，所以没有线程安全问题，可以用来处理状态机，并发请求等。但是无法利用多核优势。

## 1.2 协程 ##

介绍：http://blog.csdn.net/k\_zombie/article/details/50839961

协程不同于线程的地方在于协程不是操作系统进行切换，而是由程序员编码进行切换的，也就是说切换是由程序员控制的，这样就没有了线程所谓的安全问题。

协程的缺点：无法利用多核优势，不过，这个可以通过协程+进程的方式来解决。**如果你的任务类型不是那种cpu密集的，那选用协程是个好选择。**

1.3 多线程

参考：http://blog.csdn.net/k\_zombie/article/details/50769128

# 2 python yield和generator #

参考：http://blog.csdn.net/k\_zombie/article/details/50815256

# 3 greenlet #

The greenlet package is a spin-off of Stackless, a version of CPython that supports micro-threads called “tasklets”. Tasklets run pseudo-concurrently (typically in a single or a few OS-level threads) and are synchronized with data exchanges on “channels”.

A “greenlet”, on the other hand, is a still more primitive notion of micro-thread with no implicit scheduling; coroutines, in other words. This is useful when you want to control exactly when your code runs. You can build custom scheduled micro-threads on top of greenlet; however, it seems that greenlets are useful on their own as a way to make advanced control flow structures. For example, we can recreate generators; the difference with Python’s own generators is that our generators can call nested functions and the nested functions can yield values too. Additionally, you don’t need a “yield” keyword. See the example in tests/test\_generator.py.

Greenlets are provided as a C extension module for the regular unmodified interpreter.

Greenlets are lightweight coroutines for in-process concurrent programming.

## Who is using Greenlet? ##

There are several libraries that use Greenlet as a more flexible alternative to Python’s built in coroutine support:

>  *  [Concurrence][]
>  *  [Eventlet][]
>  *  [Gevent][]

## Getting Greenlet ##

The easiest way to get Greenlet is to install it with pip or easy\_install:

pip install greenlet
    easy_install greenlet

Source code archives and windows installers are available on the python package index at [https://pypi.python.org/pypi/greenlet][https_pypi.python.org_pypi_greenlet]

The source code repository is hosted on github: [https://github.com/python-greenlet/greenlet][https_github.com_python-greenlet_greenlet]

Documentation is available on readthedocs.org: [https://greenlet.readthedocs.io][https_greenlet.readthedocs.io]

2.2 源码分析

[python协程的实现（greenlet源码分析）][python_greenlet]：http://blog.csdn.net/fjslovejhl/article/details/38824963

[python协程入门（greenlet）][python_greenlet 1]：http://blog.csdn.net/fjslovejhl/article/details/38821673

[python greenlet背景介绍与实现机制][python greenlet]：http://blog.csdn.net/offbye/article/details/39368781

2.3

# 3 Eventlet #

官网：http://eventlet.net/

Eventlet is a concurrent networking library for Python that allows you to change how you run your code, not how you write it.

*  It uses epoll or kqueue or libevent for [ highly scalable non-blocking I/O][highly scalable non-blocking I_O].
 *  [Coroutines][] ensure that the developer uses a blocking style of programming that is similar to threading, but provide the benefits of non-blocking I/O.
 *  The event dispatch is implicit, which means you can easily use Eventlet from the Python interpreter, or as a small part of a larger application.

eventlet是一个用来处理和网络相关的 [Python][] 库函数，而且可以通过协程来实现并发，在eventlet里，把“协程”叫做greenthread(绿色线程)。

参考：

openstack nova 基础知识——eventlet：http://blog.csdn.net/xiangmin2587/article/details/8182775  
Openstack Eventlet分析(1)：http://blog.csdn.net/gaoxingnengjisuan/article/details/12913275  
Openstack Eventlet分析(2)：http://blog.csdn.net/gaoxingnengjisuan/article/details/12914831

[Concurrence]: http://opensource.hyves.org/concurrence/
[Eventlet]: http://eventlet.net/
[Gevent]: http://www.gevent.org/
[https_pypi.python.org_pypi_greenlet]: https://pypi.python.org/pypi/greenlet
[https_github.com_python-greenlet_greenlet]: https://github.com/python-greenlet/greenlet
[https_greenlet.readthedocs.io]: https://greenlet.readthedocs.io/
[python_greenlet]: http://blog.csdn.net/fjslovejhl/article/details/38824963
[python_greenlet 1]: http://blog.csdn.net/fjslovejhl/article/details/38821673
[python greenlet]: http://blog.csdn.net/offbye/article/details/39368781
[highly scalable non-blocking I_O]: http://en.wikipedia.org/wiki/Asynchronous_I/O#Select.28.2Fpoll.29_loops
[Coroutines]: http://en.wikipedia.org/wiki/Coroutine
[Python]: http://lib.csdn.net/base/python