[Twisted-Python] wsgi thread synchronization

Phil Christensen phil at bubblehouse.org
Fri Jul 27 11:42:37 EDT 2007

I'm crossposting because although my use case is in web, this is more  
of a question about dealing with threads in twisted. I have a decent  
academic understanding of threads, but I've never really used them in  
Python or Twisted.

I've just moved from a mod_python WSGI container running on prefork  
apache2 to a container running on twisted.web, and I realized that I  
now have threading considerations I didn't before.

Since my potential synchronization problems are actually quite few,  
I've been getting by just by using threading.BoundedSemaphore to  
manage a couple of thread-sensitive areas of the web app. However, I  
already have a dependency on Twisted core, so it occurs to me that  
there are probably nicer, twistier ways of doing this.

For example, I have a section of code like:

     host_tree = {}
     host_tree_lock = threading.BoundedSemaphore

     def get_application(env):
         global host_tree, host_tree_lock

         host = env.get('HTTP_HOST', env['SERVER_NAME'])


         if not(host in host_tree):

         host_node = host_tree[host]

         if not(host_node.has_path(env['REQUEST_URI'])):

         app = host_node.get_data_at(env['REQUEST_URI'])


         return app

The only variable shared between threads is the `host_tree` global  
(the `env` variable is the WSGI environment, which is unique per  
thread, and the resulting `app` object is immutable). This works for  
me and is sufficient for my needs, but I'd appreciate a sanity check  
from anyone with some thread karma to spare.

Thanks again,


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