CODEWITHSUNDEEP
pythonconcurrencymod-wsgiweb.py
seadowg
seadowg

Reputation: 4265

Keeping concurrency in web.py applications on mod_wsgi

Sorry if this makes no sense. Please comment if clarification is needed.

I'm writing a small file upload app in web.py which I am deploying using mod_wsgi + apache. I have been having a problem with my session management and would like clarification on how the threading works in web.py.

Essentially I embed a code in a hidden field of the html page I render when someone accesses my page. The file upload is then done via a standard POST request containing both the file and the code. Then I retrieve the progress of the file by updating it in the file upload POST method and grabbing it with a GET request to a different class. The 'session' (apologies for it being fairly naive) is stored in a session object like this:

class session:

    def __init__(self):

        self.progress = 0
        self.title = ""
        self.finished = False

    def advance(self):

        self.progress = self.progress + 1

The sessions are all kept in a global dictionary within my app script and then accessed with my code (from earlier) as the key.

For some reason my progress seems to stay at 0 and never increments. I've been debugging for a couple hours now and I've found that the two session objects referenced from the upload class and the progress class are not the same. The two codes, however, are (as far as I can tell) equal. This is driving me mad as it worked without any problems on the web.py test server on my local machine.

EDIT: After some research it seems that the dictionary may get copied for every request. I've tried putting the dictionary in another and importing but this doesn't work. Is there some other way short of using a database to 'seperate' the sessions dictionary?

Upvotes: 0

Views: 1445

Answers (2)

Graham Dumpleton
Graham Dumpleton

Reputation: 58523

Apache/mod_wsgi can run in multiprocess configurations and possible your requests aren't even being serviced by the same process and never will if for that multiprocess configuration each process is single thread because while the upload is occuring no other requests can be handled by that same process. Read:

http://code.google.com/p/modwsgi/wiki/ProcessesAndThreading

Possibly you should use mod_wsgi daemon mode with single multiple thread daemon process.

Upvotes: 1

frm
frm

Reputation: 3486

From PEP 333, defining WSGI:

Servers that can run multiple requests in parallel, should also provide the option of running an application in a single-threaded fashion, so that applications or frameworks that are not thread-safe may still be used with that server

Check the documentation of your WSGI server.

Upvotes: 0

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