Flask long lived global resources

0 Answers

This is a Python problem, the reason Flask and other web frameworks do not allow this/make it very difficult is because there is no defined memory model for concurrency. E.g. suppose your webserver serves requests in their own processes (e.g. Gunicorn). This will result in processes forking off the main process, and thus copying your "global" variable. If you run a server on windows then due to the lack of a fork it will instead make a new process which reimports all modules, probably producing a clean version of your global state which does not remember any changes made to it in the main process pre-thread. Or not finding it at all if you declare it behind a name guard.

There are only two possible ways to consistently do this "right". One is to build a webapp specifically to hold your global state and which is restricted to a single thread, and have your other webapp call state from this webapp.

The second, is to use Jython + threads. Since Jython runs in a JVM it has a well defined memory model with shared state, so you can use all the java EE tricks like container managed concurrency....


I'm using Flask to build my web application, and I'd like to register a global resource that represents a connection to a remote service which lasts longer than a request (in this case, the connection is a SOAP connection which can be valid for up to 30 days).

Another example could be a database like MongoDB which handles connection-pooling in the driver, and would perform badly if you created a new connection on each request.

Neither the Application Context, nor the Request Context seem appropriate for this task.

The question "Pass another object to the main flask application" suggests that we store such resources on the app.config dictionary.