Making asynchronous calls

[Simon McVittie]

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On Thu, 07 Feb 2008 at 15:06:47 +0000, Robert Rawlins wrote:
>     def timeout_func():
>         #Call To Web Service Goes Here
>         reply_cb(ReturnResultFromWebServiceCall)
>         return False
> 
>     gobject.timeout_add(500, timeout_func)
> Does that look correct? or am I missing something?

What you're missing is that I'm using timeout_add as a silly fake
example of a way to get a callback called later. What you actually want
to do is to make an async request into the web services library, i.e.
arrange for the reply_cb (or error_cb) to be called later *by the web
services library* (or by some of your code that's run by the web
services library).

So it'd look something like:

@method(...)
def DoMyCall(...)
    def ok_all_done(x):
        reply_cb(x)
    webservices.call(foo, bar, onCompleted=lambda x: ok_all_done(x))

where webservices.call is an asynchronous API provided by the library
you're calling into.

(The Python standard library's xmlrpclib module, for instance, can't be
used like this - it only has a synchronous (blocking) API.)

For instance, if your web-services calls were being made using Twisted
<http://twistedmatrix.com/projects/core/documentation/howto/async.html>,
you'd do an async call that returned a Deferred, and then do something
like:

my_deferred.addErrback(error_cb)
my_deferred.addCallback(reply_cb)

Then your error_cb or reply_cb would run at some later point when
Twisted returned to the main loop.

    Simon
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