CODEWITHSUNDEEP
c#asynchronous
Jesse McConahie
Jesse McConahie

Reputation: 316

Await Task Not returning after completion

I'm having an issue where a task is completing, but not returning back. I have a website and a web service on different servers. The website makes a call to the web service which utilizes a library with function myFunction(). If I make a call to myFunction from a console app on the web service's server, it will return as expected. However, when I make the call from the website to the web service to call myFunction(), it will get to "Step 3", but not "Step 4". I have a simplified version of the calls below.

private string myFunction()
{
    string myStr = myDoWork().GetAwaiter().GetResult();

    return myStr;
}

private async Task<string> myDoWork()
{
    logger.Debug("Step 1");
    string answer = await aFunction();

    logger.Debug("Step 4");

    return answer;
}

public async Task<string> aFunction()
{
    logger.Debug("Step 2");
    return await bFunction(CancellationToken.None);
}

AsyncLock myLock = new AsyncLock();
public Task<string> bFunction(CancellationToken cToken)
{
    return Task.Run(
        async () =>
        {
            using (await myLock(cToken))
            {
                logger.Debug("Step 3");
                result = "Hello";
                return result;
            }
        },
        cToken);
}

I'm new to async and await, so any help would be appreciated.

Upvotes: 12

Views: 14351

Answers (1)

piedar
piedar

Reputation: 2721

It's almost certainly a deadlock in myFunction(). Step 4 is scheduled to execute on the main thread, but it can't because the main thread is blocked waiting on GetResult().

It should be something closer to this:

private string myFunction()
{
    // This is NOT good style - you should avoid blocking on the result of a task.
    string myStr = Task.Run(async () => await myDoWork()).GetAwaiter().GetResult();
    return myStr;
}

private async Task<string> myDoWork()
{
    logger.Debug("Step 1");
    string answer = await aFunction();
    logger.Debug("Step 4");
    return answer;
}

public Task<string> aFunction()
{
    logger.Debug("Step 2");
    return bFunction(CancellationToken.None);
}

AsyncLock myLock = new AsyncLock();
public async Task<string> bFunction(CancellationToken cToken)
{
    using (await myLock(cToken))
    {
        logger.Debug("Step 3");
        return "Hello";
    }
}

In general, Task.Run() should be called from the highest level possible. Keep things as synchronous as possible and let the caller decide if they want to use a background thread.

Upvotes: 12

Related Questions