C# asynchronous method - help needed

Question

I have an asynchronous method that consumes a Web API action. It appears to be stuck in a loop. My reasoning for this is because if I put a break point on line 1 of the catc

Answer 1

Are you calling GetAll().Result from an ASP.NET application? Since you have tagged MVC to this question, I assume so. If you do, then you are deadlocking yourself.

Say you calling web API like this.

public ActionResult Index()
{
    var result = GetAll().Result;

    return View();
}

The problem here is when the async call completes, it needs to continue on the original thread where it jumped out but you are blocking that thread by calling Result(). Call to Result blocks and waits for async call to return and the async continuation waits for the ASP.NET thread to be available to continue. That is a dead lock.

Change your GetAll() like this.

public async Task> GetAll()
{
    try
    {
        var response = await _client.GetAsync(
                       string.Format("{0}/api/document", _baseURI))
                           .ConfigureAwait(false);

        // never hits line below
        return await response.Content.ReadAsAsync() 
                   as IEnumerable;
    }
    catch (Exception ex)
    {
        // handle exception
    }
}

This indicates the context need not be preserved when the async call is complete and hence the continuation happens in a thread pool thread (not ASP.NET).

Better yet change the action method to public async Task Index() and await GetAll().

If you find this answer helpful, you must only thank Stephen Cleary.