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']) host_tree_lock.acquire() if not(host in host_tree): _load_plugins(env) host_node = host_tree[host] if not(host_node.has_path(env['REQUEST_URI'])): _load_plugins(env) app = host_node.get_data_at(env['REQUEST_URI']) host_tree_lock.release() 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, -phil