Question

“session.identify” is a third party COM API that I call and have no access to. It performs a server query that, somehow, locks up occasionally (and thus halts the main program which is waiting for the result).

My attempt was to wrap it in an AsyncDelegate so I would be able to give it a timeout and after expiration of the timeout allow the main program to proceed (similar to this one, just with a return value). However, it still locks up without the timeout having an effect.

Am I using the AsyncHandle.WaitOne incorrectly? Could there be something in the API that prevents it from being aborted?

private delegate void AsyncIdentifyCaller(CoAudioIdSignature signature, uint numResults, uint serverFlags , out IIdentifyResult result);

private IIdentifyResult identifyAndWait(CoAudioIdSession session, CoAudioIdSignature signature, uint numResults, out IIdentifyResult iresult)
{
    AsyncIdentifyCaller identifyDelegate = new AsyncIdentifyCaller(session.Identify);

    IAsyncResult result = identifyDelegate.BeginInvoke(
        signature,
        numResults,
        0,
        out iresult,
        null,
        null);

    // wait up to timeout [ms] and then continue without a proper result 
    int timeout = 30000;
    result.AsyncWaitHandle.WaitOne(timeout, false);

    identifyDelegate.EndInvoke(out iresult, result);

    return iresult;
}

Answer 1

From what I can understand from http://msdn.microsoft.com/en-us/library/kzy257t0.aspx, you should have a logical check on the return value of WaitOne() method and wrap your logic around that

You’re running the EndInvoke regardless if a timeout ocurrs or not, thus you’re getting the same timout errors from session.Identify.

result.AsyncWaitHandle.WaitOne(timeout, false); // checks if theres is a timeout and returns true/false
identifyDelegate.EndInvoke(out iresult, result); //code to run if WaitOne returns true

You’d probably want to do this:

if(result.AsyncWaitHandle.WaitOne(timeout))
{
  identifyDelegate.EndInvoke(out iresult, result);
}
else
{
  //timeout occurred
  //handle timeout
}

UPDATE:

You might also like to check out this SO thread. The problem seems close to identical to yours. Also the accepted answer supplies a re-usable way to implement error-management