Async=true Page and WebRequest problem

[Demi]

I'm trying to use an Async="true" page to do an async HttpWebRequest. My
code is based on the MSDN example:

http://msdn2.microsoft.com/en-us/library/21k58ta7.aspx

The problem I'm having is that I'm not sure how to wait until my response
has finished arriving. It's jumping to EndGetAsyncData when I first get the
response instead of when I finish reading it. Looking at the code I can see
why it's doing this, but I'm not sure how I can fix it. I'm basically doing:

IAsyncResult BeginGetAsyncDa ta(Object src, EventArgs args, AsyncCallback cb,
Object state)
{
IAsyncResult reslt = (IAsyncResult)R equest.BeginGet Response(cb,
WebRequestState );
ThreadPool.Regi sterWaitForSing leObject(result .AsyncWaitHandl e,
new WaitOrTimerCall back(TimeoutCal lback), Request, ConnectionTimeo ut * 1000,
true);

// The response came in the allowed time. The work processing
will happen in the
// callback function.
allDone.WaitOne ();

// Release the HttpWebResponse resource if it ever got created
if (state.Response != null)
state.Response. Close();
}

void EndGetAsyncData (IAsyncResult ar)
{
RespCallback(ar );
}

Thanks for any insight!

[Joerg Jooss]

Re: Async=true Page and WebRequest problem

Thus wrote demi,
[color=blue]
> I'm trying to use an Async="true" page to do an async HttpWebRequest.
> My code is based on the MSDN example:
>
> http://msdn2.microsoft.com/en-us/library/21k58ta7.aspx
>
> The problem I'm having is that I'm not sure how to wait until my
> response has finished arriving. It's jumping to EndGetAsyncData when
> I first get the response instead of when I finish reading it. Looking
> at the code I can see why it's doing this, but I'm not sure how I can
> fix it. I'm basically doing:
>
> IAsyncResult BeginGetAsyncDa ta(Object src, EventArgs args,
> AsyncCallback cb,
> Object state)
> {
> IAsyncResult reslt = (IAsyncResult)R equest.BeginGet Response(cb,
> WebRequestState );
>
> ThreadPool.Regi sterWaitForSing leObject(result .AsyncWaitHandl e,
> new WaitOrTimerCall back(TimeoutCal lback), Request, ConnectionTimeo ut *
> 1000,
> true);
>
> // The response came in the allowed time. The work
> processing
> will happen in the
> // callback function.
> allDone.WaitOne ();
> // Release the HttpWebResponse resource if it ever got
> created
> if (state.Response != null)
> state.Response. Close();
> }
> void EndGetAsyncData (IAsyncResult ar)
> {
> RespCallback(ar );
> }
> Thanks for any insight![/color]

This seems to be one of the most popular pitfalls.

You cannot wait on the *callback's* completion using the AsyncWaitHandle .
Once the callback is called, the asynchronous operation
is completed -- that's why IsComplete will be true as well.

In order to wait for your callback's completion, use your own EventWaitHandle ,
and Set() it at the end of your callback.

Cheers,
--
Joerg Jooss
news-reply@joergjoos s.de