Synchronize method invocations

When I want to synchronized method invocations, I often want to cancel an attempt if the method is already running, as opposed to queueing up another execution instance. Here’s an example of how to do that:

public ActionResult Test()
{
    var semaphore = new Semaphore(1, 1, MethodBase.GetCurrentMethod().Name);
    if (!semaphore.WaitOne(0))
    {
        return Content($"failure: method is already running in another context");
    }
    
    try
    {
        Thread.Sleep(5 * 1000);
        return Content("success");
    }
    catch (Exception e)
    {
        return Content($"failure: {e.Message}");
    }
    finally
    {
        semaphore.Release();
    }
}

This method will run and take 5 seconds to complete. If this method is run again during that time, it will return without executing the try/catch/finally block, with an error message. Also, finally block is required to release the semaphore so that this method can be executed again.

When testing concurrency of a web app, keep in mind that many browsers won’t run multiple page fetches to the same site simultaneously.