[sldev] What is eventlet, and why should you care?

[Donovan Linden]

Introduction
=====
I'm Donovan Linden (Donovan Preston). I started at Linden in May of  
2006 to join Zero Linden (Mark Lentczner) in forming Studio Icehouse,  
whose charter is to "modernize" the second life protocol. We have  
been slowly doing this by introducing LLSD, capabilities, and  
designing web services in a REST-style fashion.

I have been using Python since 2000, and using non-blocking network I/ 
O (with the Twisted framework) for most of that time. When I started  
at Linden, I decided to see if I could use a small open source  
coroutine-based networking framework, eventlet, written by a friend  
of mine, Bob Ippolito.

Eventlet
=====
Why would I want to use eventlet? Eventlet uses coroutines (with the  
help of the greenlet module) to perform high scalability non-blocking  
I/O while appearing to the programmer to block. This means code that  
looks like:

socket.write('hello world')

Is actually causing a coroutine switch away from this coroutine into  
a mainloop coroutine, until the syscall select or poll says that  
socket's file descriptor is ready for writing. This gives a nice  
balance between the advantages of non-blocking I/O (no preemption and  
thus no possibility of deadlock, deterministic control flow) and  
blocking I/O (ease of use, ease of composition, ease of error handling).

Usage of eventlet inside of Linden has been a great success. Several  
key services have been ported from C++ code which depends on the  
central database to distributed Python web services (the "backbone"  
architecture). We think the code is small, simple, clear, and  
powerful, and we invite others to take a look!

How can you help?
=====
First, I invite you to read the eventlet wiki page, download  
eventlet, and try out the examples.

http://wiki.secondlife.com/wiki/Eventlet

Second, Which Linden and I have put together a roadmap for what we  
would like to do before declaring eventlet "1.0" and doing an  
official release. Please take a look and see if there is anything you  
could help with!

http://wiki.secondlife.com/wiki/Eventlet_1.0

Donovan Preston