Thanks for the helpful answer!
On 20 Mai, 01:18, Yarko Tymciurak <resultsinsoftw...@gmail.com> wrote: > On May 19, 5:41 pm, amoygard <amoyg...@gmail.com> wrote: > > > Thanks for the answer - I was aware that I don't have to do this to > > handle ajax requests in general. The application I'm building needs to > > send and receive a sequence of messages from the client in a specific > > order, so I thought it would be easier to handle it in one thread/ > > process. It is however probably better to do it statelessly as you > > say, so I'll probably have to rewrite the code somewhat. > > > Out of curiosity though, what is the right way to start a subprocess > > in web2py? > On Wed, May 19, 2010 at 10:41 PM, amoygard <amoyg...@gmail.com> wrote: > > Thanks for the answer - I was aware that I don't have to do this to > handle ajax requests in general. The application I'm building needs to > send and receive a sequence of messages from the client in a specific > order, so I thought it would be easier to handle it in one thread/ > process. It is however probably better to do it statelessly as you > say, so I'll probably have to rewrite the code somewhat. > > Out of curiosity though, what is the right way to start a subprocess > in web2py? > > In general, you don't - unless you have a long-running process that is > divorced from http requests coming in from the network (for long > running processes, there is a sort of "cron" facility). > > In a hosting environment, you have apache/wsgi (for example) running a > wsgi-thred that is web2py - that (main and the stuff in gluon) is your > long-running process (er, thread). To restart web2py, with wsgi, you > would do what is normal (touch a file) to cause apache to re-start > that wsgi thread. Other than from something like a terminal on your > server, you do not do this (it would not be uncommon for this to run > year-long without a restart). > > Within web2py, you have a number of threads: db connection pools, and > application threads; again, these respond to requests, and are > spawned off by web2py (not you) - Massimo, or someone who has dug into > this recently could comment on how that works - but frankly, that is > not important. > > Your web app _is_ running in a stateless environment: web requests. > You have a way to "capture" some state on your own: sessions. > > I only know of one framework that uses the tasklet facility of > stackless, and that's nagare --- it seems to use a tasklet to wait > for a return so that you seem to generate a view inline in your > code. In web2py, your (for example) default/index() controller is > typically called multiple times, and decides (though it's mostly > masked from you) through logic if it's an initial request, or a > response --- i.e., when you call something with a form, there is a > check by means of form.accepts() to see if the response variables are > populated, and (somewhat behind the scenes) all the stacks of > appropriate validators are run. This is why you see things like > form.accepts() success or fail conditions, and fall thru if neither > (i.e. not a response yet). > > So - in general, you do not start subprocesses - with the exception of > cron. Seehttp://www.web2py.com/book/default/section/4/17 > > - Yarko > > > > > > > On 19 Mai, 22:00, Yarko Tymciurak <resultsinsoftw...@gmail.com> wrote: > > > > On May 19, 2:14 pm, amoygard <amoyg...@gmail.com> wrote: > > > > > Hi, > > > > > I'm pretty new to web2py and web application frameworks. I'm trying to > > > > create a new background process in controller to handle incoming ajax > > > > data from a user. > > > > You are trying to do too much: remember: the web is "stateless" --- > > > when _anything_ comes in from a client that gets directed to your URL, > > > (this is just an example flow, so you can get the general idea): > > > > - somewhere, a DNS server replaces the URI name with a destination > > > address; > > > - the destination server (let's say apache) tries to sort out, and > > > direct to the correct app (in this case, web2py); > > > - web2py's main() parses the path part of the URI to decide how to > > > route internally > > > - if it finds a matching app/controller, main() will set up the > > > execution environment to prepare the call: > > > - i.e., your models are "executed" so that the table definitions, > > > etc. are all in the environment, and then your controller file > > > - the function in your controller is called with this execution > > > environment (this is the thread that you are trying to make, and > > > should not bother) > > > > The controller function does it's stuff with the request, and returns > > > (to main()) the response - sometimes nothing, sometimes a dict. of > > > stuff; > > > Main takes the return values from the controller, and processes > > > appropriately, most often getting the view, parsing the template, > > > creating the resulting view, and sending it back to the client. > > > > When an ajax call is made, you can see an example > > > athttp://www.web2py.com/book/default/section/10/3, and explanation of > > > what this does. > > > > The general point: you call a controller with a request (even in the > > > case of an ajax call); > > > The response goes back to the caller. > > > > Lots of stuff happens for you - you don't need to write the entire web > > > server underpinnings; just worry about the logic you want to > > > implement so server and client can converse / exchange information. > > > > Hope this helps. > > > > Regards, > > > - Yarko > > > > > I'm using the module multiprocessing for this. > > > > However, when I start the new process, a new instance of web2py server > > > > is started? I'm assuming this has something to do with forking (which > > > > I don't know much about). Is there an easy workaround? Or should I > > > > preferrably do this some other way, for instance with threads? > > > > > Code is as follows (controller calls function 'someinit' in a module > > > > in module-folder): > > > > > def tekstpr(mstring,conn): > > > > print mstring > > > > conn.send("hello") > > > > > def someinit(userid): > > > > from multiprocessing import Pipe, Process > > > > parent_conn, child_conn = Pipe() > > > > p = Process(target=tekstpr,args=("I'm alive!",child_conn)) > > > > session.procpipe = parent_conn > > > > p.start() > > > > session.procpipe.poll(300) > > > > return session.procpipe.recv()
