Question

I want to be able to measure the time it take to execute an asynchronous method.

When I call the method synchronously, I run the following code and I get the exact amount of time it took a the method MyMethod.

for (int i = 0; i < 5000; i++) {
    stopWatches[i].Start();
    webService.MyMethod(new Request());
    stopWatches[i].Stop();
}

I changed my code to execute MyMethod asynchonously, so now my code looks like this.

var callback = new Action<IAsyncResult>(ar => {
    int i = (int)ar.AsyncState;

    try {
        var response = webService.EndMyMethod(ar);
        stopWatches[i].Stop();
    }
}

for (int i = 0; i < 5000; i++) {
    webService.BeginMyMethod(new Request(), new AsyncCallback(callback), i);
    stopWatches[i].Start();
}

The problem is that the stopwatches don’t measure the time required to execute a request anymore. They measure the time from when a request entered in the ThreadPool queue until the end of the call. So I end up with a list of stopwatches with a time going up linearly.

How do I fix my stopwatches? Is there a way to know exactly when the request start?

Thanks!

UPDATE: I cannot change the implementation of MyMethod.

Answer 1

Create a method BeginTimedMyMethod, not in the webservice class. In the implementation of BeginTimedMyMethod, call an intermediate method instead of MyMethod that is called asynchronously. Start the stopwatch there, then call MyMethod.

void BeginTimedMyMethod(...)
{
    //create delegate with StartMethod as target
    //Invoke StartMethod delegate
}

void StartTimedMethod(Request request)
{
    stopWatches[i].Start();
    webservice.MyMethod(request);
}