Following code:

var r = WebRequest.Create(uri);
ManualResetEvent re = new ManualResetEvent(false);
r.BeginGetRequestStream(x =>
                {
                    re.Set();
                    rs = r.EndGetRequestStream(a_r);
                }, null);
                re.WaitOne();

run OK.But this:

var r = WebRequest.Create(uri);
ManualResetEvent re = new ManualResetEvent(false);
r.BeginGetRequestStream(x =>
                {
                    
                    rs = r.EndGetRequestStream(a_r);
                    re.Set();//change
                }, null);
                re.WaitOne();

just hangs forever.
According to docs x=>{} lambda executed in "worker thread",but in "EndGetRequestStream" we see "AsyncHelper.BeginOnUI->UiSynchronizationContext.Current.Send()" for lambda,so we have deadlock. How understand(and resolve) that statement?

Thanks.