July 29, 2008

Eventlet 0.7 and Spawning 0.7 Released

Eventlet 0.7

Eventlet 0.7 fixes some very long-standing bugs. First of all, there was a CPU leak in the select hub which would cause an http keep-alive connection to consume 100% CPU while it was open. The problem was that every file descriptor was being passed in to select, even if the callback for the readiness mode was None. This bug has been in since the very beginning of eventlet, and it's great to have it fixed!

Second, another old bug. It's now possible to use Eventlet's SSL client to talk to Eventlet's SSL server. There was a subtle bug in the way SSL sockets would raise an error in some conditions instead of returning '' to indicate the connection was closed.

Finally, some memory leaks in the libevent and libev hubs (fairly new code) were fixed, so if you're using Eventlet with libevent or libev try it out and see how it performs for you.

Also, this release pulls in a bunch of API additions from the Linden SVN repository. Ryan Williams is now maintaining an HG repository which is synched with the SVN repository, so integrating patches between branches will now be much easier.

Update July 30, 2008This release of eventlet also supports stackless-pypy again. I had to check for the absence of the socket.ssl object, and re-enable the poll hub. To try this out, check out and translate pypy-c following the instructions on the pypy site, and then run one of the eventlet examples (for example, "./pypy-c /Users/donovan/src/eventlet/examples/wsgi.py")

Download Eventlet 0.7 from PyPI: http://pypi.python.org/pypi/eventlet/0.7

Spawning 0.7

Spawning has improved a lot since I last wrote about it. It now has a command line script, "spawn", which makes it easy to quickly serve any wsgi application. The concurrency strategy is also now extremely flexible and can be configured for a plethora of use cases.

The default is to use one non-blocking i/o process with a threadpool, which makes it easy to use with any existing wsgi applications out there that assume shared memory and the ability to block.

However, it's possible to independently configure the number of i/o processes, the number of threads, and even configure it to be single-process, single-thread, with fully non-blocking i/o (thanks to eventlet's monkey patching abilities).

Update July 30, 2008This release of spawning also has an experimental Django factory. To run a Django app under Spawning, run "spawn --factory=spawning.django_factory.config_factory mysite.settings".

Take a look at the Spawning PyPI entry for more information: http://pypi.python.org/pypi/Spawning/0.7

Posted by Donovan at 4:33 PM | Comments (3)



June 16, 2008

Spawning 0.1 Released

Spawning is an experimental mashup between Paste and eventlet. It provides a server_factory for Paste Deploy that uses eventlet.wsgi. It also has some other nice features, such as the ability to run multiple processes to take advantage of multicore processors and multiprocessor machines, and graceful code reloading when modules change or the svn revision of a directory changes. Graceful reloading means new processes are immediately started which start serving new incoming requests, but old processes hang around processing the old requests until those requests are complete.

This is very early still. The code is currently hard-coded to run one process, but once I figure out how to use Paste Deploy's configuration files a bit better I will make it configurable. I mostly wanted to get it out quickly because Ian Bicking asked for it in the comments of my last blog post, and to get feedback. I'd like more of this code to be shared between Spawning and mulib's 'mud' server. I also need a better name than Spawning.

You can download a tarball here or you can clone the Mercurial repository here.

Posted by Donovan at 7:10 PM | Comments (1)



June 12, 2008

Eventlet 0.5 Released

The last release of eventlet was 0.2, which we did when we re-open-sourced the fork of eventlet I worked on while I was at Linden Lab. 0.2 was released quite a while ago, and eventlet has seen significant improvement in the meantime.

The main change in this release is the ability to use libevent as the multiplexing api instead of raw select or poll. If libevent and the Python wrapping are not installed, eventlet will still fall back, first checking for the presence of poll and falling back to select if it is not available.

Another major change in this release is a much improved eventlet.wsgi server. The wsgi server now supports Transfer-Coding: chunked as well as Expect: 100 Continue, and is quite fast. I tested it against an eventlet based wsgi server I wrote which uses wsgiref (from the Python 2.5 standard library) and my informal tests showed eventlet.wsgi being several hundred requests a second faster at serving a "Hello, World!" wsgi application.

This release also features significant refactoring, cleaner code, support for cooperative operations on pipes (and unix domain sockets) as well as sockets, more tests, and docstrings for pretty much everything. The documentation, which was non-existant before, is now pretty comprehensive.

To install, just "easy_install eventlet" and start hacking!

Posted by Donovan at 11:49 AM | Comments (10)



June 2, 2008

REST + Actors

I had a really good idea over the weekend for using eventlet and mulib to combine the concepts of REST and Actors. Eventlet has had an Actor class for a while now, but I haven't really used it for anything. After otakup0pe twittered a link to the Reia language (everyone knows how much of a language geek I am) I started thinking about Actors again and how I could have applied them to various work problems I solved in the last few years. The last time I really tried to do anything serious with Actors was when I wrote the latest version of Pavel on top of the just-written (at the time) eventlet. I also tried to mix a prototype object system in there and the actor coroutines were implicit in the semantics of usage (an Actor which called a method on another Actor would be implicitly causing a switch into the other Actor's coroutine), which in retrospect was perhaps a bit too ambitious.

Ryan Williams wrote the current eventlet Actor (eventlet.coros.Actor) and it's much simpler and more straightforward: You override the received method to handle messages, and other actors call the cast method to send messages. This is different from my previous implementation (and also what my ideal would be) in that you get called back for every message, meaning the main coroutine is generic and there's no need to keep track of where the Actor's coroutine is to serialize an actor. This means it would be possible to request a representation of an Actor at any time between messages. The state would include all the Python instance variables along with all the unhandled messages currently in the Actor's mailbox.

So, with that realization, it suddenly becomes trivial to write a mulib handler for the Actor class. GET and PUT with the appropriate content types (application/json for example) would get or set the current state of the Actor. DELETE would delete it. POST enqueues a message in the actor's mailbox (it just calls cast with the body of the request). Simple and straightforward. I'm totally going to do this soon -- it probably would have been faster to just do the implementation rather than blog about it :-)

Oh, one more thing -- to enhance the experience of actually using these semantics, the cast method should become a generic method that dispatches based on pattern matching (using mulib.shaped). I haven't figured out what an efficient implementation of this would look like yet, but I'm going to try a brute-force implementation just for fun.

Posted by Donovan at 10:42 AM | Comments (0)



May 14, 2008

Template on PUT

I just had a cool idea. Usually, people run HTML templating engines on GET. They fetch some data, load an HTML template, and then mash the two together. My idea is to instead run the templating engine on PUT. The body of the PUT would have the data to be templated. The URL that was PUT to would determine which template to use. The response from the PUT would contain the fully templated output, equivalent to what the client would get by doing a GET to that url at any point afterwards.

Posted by Donovan at 12:55 PM | Comments (2)



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