> >>> The second is a problem I see an app I'm working on heading towards. > >>> The app has web-alterable configuration, so in a multi-threaded and > >>> particular multi-process environment, I need some way to get the > >>> other threads or processes to re-read their configuration when it has > >>> changed. > >> > >> In Paste/Pylons the configuration is stored in the environment (which > >> is per-request), and put into a threadlocal object for access. > > > > Again, how about across processes? > > And if the configuration changes once the app is up and running, how do > > you propogate changes to all the other app processes? > > Generally you'd want to kill all the worker processes and start over. > If you have a reasonable way to do that (and I think mod_wsgi would give > you a reasonable way to do that), restarting the process is always > cleanest. I believe even something like Apache's "graceful" > restart/reload just restarts the server, while letting existing requests > finish.
Yes, with Apache one can use 'graceful'. That will cause applications running under either mod_wsgi embedded mode or daemon mode to be restarted. For daemon mode, in mod_wsgi 2.0 there is also 'Process' reload mechanism as an option. Just touching the main WSGI script file entry point will cause just the processes for that daemon process group to be restarted on next request, thereby avoiding a restart of the whole Apache web server and any other hosted applications. Thus, change your config file, whether it be actual Python code or an ini file and touch the main WSGI script file for that application. Upon the next request against that application it will detect WSGI script file has changed and will do the restart. If you wanted to force the restart without waiting for next request to arrive, then you can also just send a SIGINT to all processes in that daemon process group. The trick is knowing which processes they are, because if still run as Apache user, hard to tell them from normal Apace child processes since they are just a fork of main Apache process. If mod_wsgi told to change them to run as different user, somewhat easier. This sort of process reload mechanism based on script file change is also available in things like mod_fastcgi. Based on comments made by various people, not sure how reliable it is in mod_fastcgi though. For other options on how to trigger automatic reloading of application process in mod_wsgi when code and/or config changes see: http://code.google.com/p/modwsgi/wiki/ReloadingSourceCode Latter example in this based on similar stuff that Ian has done, just customised to the setting of mod_wsgi and that one can rely on mod_wsgi to automatically restart a daemon process when killed off. Thus bit different to where this sort of idea is used elsewhere to trigger in process reload of modules on top of existing modules, which will not always work because of dependencies between modules. Graham _______________________________________________ Web-SIG mailing list Web-SIG@python.org Web SIG: http://www.python.org/sigs/web-sig Unsubscribe: http://mail.python.org/mailman/options/web-sig/archive%40mail-archive.com
