Hello Jason, Thank you very much for your kind and swift offer. I'll do it gladly ... but I need to set-up Skype on my station :-( and register a Skype account. I'm an old-timer and my only contact is Gmail. I have no G+, no Facebook, no Twitter, ...
What is your preferred day and time for a Skype call. I live in the Paris-Luxembourg-Brussels time zone. For instance it is now Saturday Aug. 2, 20:05. When you say privately, I suppose a one-to-one call on Skype and I suppose I can easily find your name there. Have a nice Sunday and thanks again, René On Saturday, August 2, 2014 6:35:33 PM UTC+2, Jason Garber wrote: > > Hi Rene, > > I offer to do a skype call with you to review all of this as I have been > there done that and have a crisp understanding of all the working parts. > > Contact me privately if you want to do this. > > Thanks, > Jason > On Aug 2, 2014 12:32 PM, <[email protected] <javascript:>> wrote: > >> Dear Graham & al., >> >> Congratulations for your software and documentation. I have however some >> difficulties as outlined in the subject caption. >> >> I'm building a case study for an application on an intranet within a >> company where the users would interact with their browser communicating >> with the Apache2/mod_wsgi server (daemon mode + multi-threads). >> >> However I'm afraid I'm misunderstanding some important underlying >> concepts of the architecture. Please allow me to give an example and to >> give you my thoughts - which could go wrong somewhere. >> >> *Part 1:* >> >> I wrote a simple HTML page with a one field input form. >> >> In my `environment` dictionary, I have, among other key/value pairs, the >> following: >> >> REQUEST_METHOD: POST >> REQUEST_URI: /core/my-wsgi-app >> mod_wsgi.callable_object: application >> >> The first two values come obviously from my html <form >> action="core/my-wsgi-app" method="post">...</form>, and the third value is >> the default value in the configuration directive (WSGICallableObject >> application). >> >> In my my-wsgi-app script, I have of course: >> >> def application (environment, start_response): >> [my code here] >> return [response_body] >> >> So all is fine and works well but there is something I don't get (I mean >> I haven't fully assimilated), certainly in a multi-users, multi-threads, >> ... environment. The main question is about the WSGICallableObject. >> >> The documentation ( >> https://code.google.com/p/modwsgi/wiki/ConfigurationDirectives#WSGICallableObject) >> >> says "*The WSGICallableObject directive can be used to override the name >> of the Python callable object in the script file which is used as the entry >> point into the WSGI application.*" [underlining is mine]. For me the >> WSGI application is the whole application: when finished the target >> application I'm case studying could serve one hundred users, delivering >> thousands of pages built dynamically over hundreds of SQL tables, ... Am I >> right in thinking than one entry point would be fit for such purpose. The >> size of the application is such that I already opted for a daemon >> configuration with multi-threads (I do not wish to have users waiting in a >> single queue because one of them is building a page that takes seconds to >> assemble). >> >> Having one single callable object seems to give me these only 4 options: >> >> 1) Have only one single REQUEST_URI, say /core/my-wsgi-app, where only >> one callable object (function, class, ...) is used under the one and same >> name (application). In such case that callable object is the one and only >> full single entry point to the overall application (thousands of pages >> built dynamically) and I must care for checking, authorisation, parsing, >> dispatching, ... and finally assembling the response and returning it. I'm >> wondering if this single script/callable-object could become a bottleneck. >> It is the concern I've just expressed. Of course, Python can handle >> hundreds of function calls and instance calls. This option makes me doubt I >> fully understand the mechanism. I call this option N to 1. >> >> 2) Have various REQUEST_URI (even one per page if need be) and in each >> called script, there would be one callable object with the same name >> ("application" as defined in the WSGICallableObject directive). In that >> case, I could create a callable instance of a base class but that instance >> should bear the application name and use the two positional arguments >> passed by mod_wsgi. This option, if used exclusively, seems to me like a >> normal "CGI static serving", i.e. one request activates one script (the >> whole logic and dynamism is in the script). This point too makes me doubt I >> understand the real nature of WSGI. I call this option N to N. >> >> 3) One could combine option 1 and 2 to create more dynamism without >> risking the potential (?) bottleneck of option 1 when used alone. I call >> this option N to M (<<N) >> >> 4) There seems to be a possibility to define the WSGICallableObject per >> directory. My understanding is that the REQUEST_URI belonging to a >> directory (and its sub-directories) would use that callable object name. >> This means for instance that any URI of the form /core/section-1/abc would >> have a callable object Application_1, while any URI under >> /core/section-N/... would have a callable object Application_N. I haven't >> tried this directive yet so I may misunderstand its role. >> >> This is my overall understanding but I'm afraid I'm missing something >> fundamental [please note that I'm not an English speaker and I might have >> missed subtleties in the documentation which is quite dense]. I tried to >> picture this in a diagram but I'm not sure I got it right: >> >> M (html requests) -> 1 (http server) -> N x P (mod_wsgi daemons x >> threads) -> X? (Python instance(s) / one per daemon ? I don't know) -> M >> (calls to one object in one URI or to many objects - named the same - in >> many URI ? ) and back to the user via the same route. >> >> I assume that one user html request generates ultimately one call to a >> callable object (give or take) : that's why I use M in toth cases. Is this >> assumption correct ? My dilemma is that I can't understand the spread of >> the load between the 2 extremes: one URI containing the `application` >> callable object (that is eventually called hundreds of times per second) or >> many hundreds URI each containing a callable object named `application` >> that all get called much less frequently. >> >> *Part 2:* >> >> As a consequence of this hazy understanding of mine, I wonder why can't >> the name of the callable object be chosen on demand ? >> >> If I refer to PEP3333 (http://legacy.python.org/dev/peps/pep-3333/) I >> understand that: >> " >> *A server or gateway must invoke the application object using positional >> (not keyword) arguments. (E.g. by calling result = application(environ, >> start_response)*" >> >> So my guess is that, still referring to the example at the top, one >> thread in mod_wsgi loads (I wouldn't call this an import) the >> /core/my-wsgi-app script and calls application(environment, start_response) >> that has been defined in it. Is this the correct mechanism ? >> >> Could we imagine that mod_wsgi would sometime call my_App (arg1, arg2), >> some other time call your_App (req, resp) or call Small_app (in, out) where >> my_App, your_App, Small_app would be defined because mod_wsgi would be able >> to set dynamically the WSGICallableObject . Imagine that in the >> WSGIImportScript script file, we would have: >> >> def my_App (param1, param2): >> [code here] >> return [my_Response] >> >> def your_App (param1, param2): >> [code here] >> return [your_Response] >> >> def Small_app (param1, param2): >> [code here] >> return [Small_response] >> >> all the functions would be ready to be called. >> >> I suppose that in any case we are limited: >> >> A) by the HTTP protocol (URI given via the action attribute, the POST, >> GET, OPTIONS, ... from the method attribute and the key/value pairs from >> the various input fields); and >> >> B) by directives we could give to configure mod_wsgi. I guess it is not >> the role neither the intend to build some "user logic" within mod_wsgi. >> >> *Conclusions:* >> >> 1) Am I correct in my understanding of mod_wsgi as expressed here above >> (Part 1) ? Beware that I could be out of my depth, i.e. talking about >> something I don't properly understand. In that case please correct me or >> complement my view. >> >> 2) Do we need to dynamically choose the callable object name for the sake >> of dynamism and multiplicity ? >> >> -> If not, the current set-up is enough. In which case is the preceding >> point ( 1) ) complete and correct ? >> >> -> If yes, how to do it simply and elegantly ? >> >> => Idea 1: create an extra key/value pair (e.g. >> wsgi_callable_object=my_application). It seems cumbersome to me. >> >> => Idea 2: if the URI were to have the form >> /core/my-wsgi-app/_my_application then mod_wsgi could provide: >> REQUEST_URI: /core/my-wsgi-app >> mod_wsgi.callable_object: my_application >> in the 'environment` dictionary because it would strip the >> trailing part beginning with an underscore provided it is told to do so by >> a directive; >> otherwise it would behave as now and deliver: >> REQUEST_URI: /core/my-wsgi-app/_my_application >> mod_wsgi.callable_object: application >> >> *Thanks:* >> >> I do realize this is an unusual post (maybe it should find its way in the >> group working on the documentation) but I would be very happy if some of >> you could answer / feedback to me. In any case I do thank you all in >> advance. >> >> René >> >> -- >> You received this message because you are subscribed to the Google Groups >> "modwsgi" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To post to this group, send email to [email protected] >> <javascript:>. >> Visit this group at http://groups.google.com/group/modwsgi. >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "modwsgi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/modwsgi. For more options, visit https://groups.google.com/d/optout.
