Async=true Page and WebRequest problem

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

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 BeginGetAsyncData(Object src, EventArgs args, AsyncCallback cb,
Object state)
{
IAsyncResult reslt = (IAsyncResult)Request.BeginGetResponse(cb,
WebRequestState);
ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle,
new WaitOrTimerCallback(TimeoutCallback), Request, ConnectionTimeout * 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!
 
Thus wrote 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 BeginGetAsyncData(Object src, EventArgs args,
AsyncCallback cb,
Object state)
{
IAsyncResult reslt = (IAsyncResult)Request.BeginGetResponse(cb,
WebRequestState);

ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle,
new WaitOrTimerCallback(TimeoutCallback), Request, ConnectionTimeout *
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!
Click to expand...

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,
 
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