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Does it make sense to call only one `async` method and `await` for it in another `async` method?

Does it make sense to call only one async private method and await for it in another async method?
Example:
private async Task<string> ReadMyFileAsync()
{
var streamReader = new StreamReader(#"c:\myFile.txt")
return await streamReader.ReadToEndAsync(); // <-- Does it make sense for me here to await for only onething, while the caller of the method ReadMyFileAsync is already an async method?
// By ignoring that the stream should be disposed...
}
private string ReadMyFile()
{
var streamReader = new StreamReader(#"c:\myFile.txt")
return streamReader.ReadToEnd();
// By ignoring that the stream should be disposed...
}
public async void OnFileChangedHandler()
{
// Some work...
var myText = await ReadMyFileAsync(); <-- Does it make any difference whether I called `await ReadMyFileAsync()` or `ReadMyFile()`?
var someThingElse = await SomeThingElse(...);
// Some work...
}
In the scenario above, what I guess, even if the method ReadMyFileAsync was called in its syncronous version (without using async and by using ReadToEnd() instead of await ReadToEndAsync()), it will keep acting the same, because the caller method is an async method. Which means in my opinion, this will make sense only if I am trying to read multiple files in paralell (see the following as example), is that right?
private async Task<string> ReadMyFileAsync() // <-- This makes sense for me
{
var streamReader1 = new StreamReader(#"c:\myFile1.txt");
var streamReader2 = new StreamReader(#"c:\myFile2.txt");
var streamReader3 = new StreamReader(#"c:\myFile3.txt");
var myText1Task = streamReader1.ReadToEndAsync();
var myText2Task = streamReader2.ReadToEndAsync();
var myText3Task = streamReader3.ReadToEndAsync();
return await myText1Task + await myText2Task + await myText3Task;
// By ignoring that the streams should be disposed...
}
So the question is simply, in the first block of code, does it make any difference whether I called ReadMyFileAsync or ReadMyFile?
Update: The whole question simplified is:
If I am going to await for the async method ReadMyFileAsync inside my async method OnFileChangedHandler, why would I use ReadMyFileAsync over ReadMyFile?

It depends. If you really only call one other method and you have no side effects, then you could just return the Task instead of awaiting it and returning the result wrapped in a task.
However, even in your example, you have side effects. You need to .Dispose something and you need to know when to do that. So you cannot just return the task, you need to wait until it's finished, then dispose your resources and then return the result of the finished task. Since it's "not that simple" even in your own boiled down example, the answer is: it does make sense. You have to decide case-by-case.
Sometimes you can just pass the task along, then the method does not need to be async at all, it just needs to return a Task and sometimes you need to do things based on the timing of tasks (i.e. do this only after that other thing is finished) and then you need to use async methods because you want to await results.

Yes, you should prefer async methods over sync because async methods doesn't block the executing thread. In UI apps it means that UI won't freeze. In Server apps it means that your server will be able to run more concurrent work without starving the threads.

How to convert WaitAll() to async and await

Is it possible to rewrite the code below using the async await syntax?
private void PullTablePages()
{
var taskList = new List<Task>();
var faultedList = new List<Task>();
foreach (var featureItem in featuresWithDataName)
{
var task = Task.Run(() => PullTablePage();
taskList.Add(task);
if(taskList.Count == Constants.THREADS)
{
var index = Task.WaitAny(taskList.ToArray());
taskList.Remove(taskList[index]);
}
}
if (taskList.Any())
{
Task.WaitAll(taskList.ToArray());
}
//todo: do something with faulted list
}
When I rewrote it as below, the code doesn't block and the console application finishes before most of the threads complete.
It seems like the await syntax doesn't block as I expected.
private async void PullTablePagesAsync()
{
var taskList = new List<Task>();
var faultedList = new List<Task>();
foreach (var featureItem in featuresWithDataName)
{
var task = Task.Run(() => PullTablePage();
taskList.Add(task);
if(taskList.Count == Constants.THREADS)
{
var anyFinished = await Task.WhenAny(taskList.ToArray());
await anyFinished;
for (var index = taskList.Count - 1; index >= 0; index--)
{
if (taskList[index].IsCompleted)
{
taskList.Remove(taskList[index]);
}
}
}
}
if (taskList.Any())
{
await Task.WhenAll(taskList);
}
//todo: what to do with faulted list?
}
Is it possible to do so?
WaitAll doesn't seem to wait for all tasks to complete. How do I get it to do so? The return type says that it returns a task, but can't seem to figure out the syntax.## Heading ##
New to multithreading, please excuse ignorance.

Is it possible to rewrite the code below using the async await syntax?
Yes and no. Yes, because you already did it. No, because while being equivalent from the function implementation standpoint, it's not equivalent from the function caller perspective (as you already experienced with your console application). Contrary to many other C# keywords, await is not a syntax sugar. There is a reason why the compiler forces you to mark your function with async in order to enable await construct, and the reason is that now your function is no more blocking and that puts additional responsibility to the callers - either put themselves to be non blocking (async) or use a blocking calls to your function. Every async method in fact is and should return Task or Task<TResult> and then the compiler will warn the callers that ignore that fact. The only exception is async void which is supposed to be used only for event handlers, which by nature should not care what the object being notified is doing.
Shortly, async/await is not for rewriting synchronous (blocking code), but for easy turning it to asynchronous (non blocking). If your function is supposed to be synchronous, then just keep it the way it is (and your original implementation is perfectly doing that). But if you need asynchronous version, then you should change the signature to
private async Task PullTablePagesAsync()
with the await rewritten body (which you already did correctly). And for backward compatibility provide the old synchronous version using the new implementation like this
private void PullTablePages() { PullTablePagesAsync().Wait(); }

It seems like the await syntax doesn't block as I expected.
You're expecting the wrong thing.
The await syntax should never block - it's just that the execution flow should not continue until the task is finished.
Usually you are using async/await in methods that return a task. In your case you're using it in a method with a return type void.
It takes times to get your head around async void methods, that's why their use is usually discouraged. Async void methods run synchronously (block) to the calling method until the first (not completed) task is awaited. What happens after depends on the execution context (usually you're running on the pool). What's important: The calling method (the one that calls PullTablePAgesAsync) does not know of continuations and can't know when all code in PullTablePagesAsync is done.
Maybe take a look on the async/await best practices on MSDN

Calling async methods from a synchronous context

I'm calling a service over HTTP (ultimately using the HttpClient.SendAsync method) from within my code. This code is then called into from a WebAPI controller action. Mostly, it works fine (tests pass) but then when I deploy on say IIS, I experience a deadlock because caller of the async method call has been blocked and the continuation cannot proceed on that thread until it finishes (which it won't).
While I could make most of my methods async I don't feel as if I have a basic understanding of when I'd must do this.
For example, let's say I did make most of my methods async (since they ultimately call other async service methods) how would I then invoke the first async method of my program if I built say a message loop where I want some control of the degree of parallelism?
Since the HttpClient doesn't have any synchronous methods, what can I safely presume to do if I have an abstraction that isn't async aware? I've read about the ConfigureAwait(false) but I don't really understand what it does. It's strange to me that it's set after the async invocation. To me that feels as if a race waiting to happen... however unlikely...
WebAPI example:
public HttpResponseMessage Get()
{
var userContext = contextService.GetUserContext(); // <-- synchronous
return ...
}
// Some IUserContextService implementation
public IUserContext GetUserContext()
{
var httpClient = new HttpClient();
var result = httpClient.GetAsync(...).Result; // <-- I really don't care if this is asynchronous or not
return new HttpUserContext(result);
}
Message loop example:
var mq = new MessageQueue();
// we then run say 8 tasks that do this
for (;;)
{
var m = mq.Get();
var c = GetCommand(m);
c.InvokeAsync().Wait();
m.Delete();
}
When you have a message loop that allow things to happen in parallel and you have asynchronous methods, there's a opportunity to minimize latency. Basically, what I want to accomplish in this instance is to minimize latency and idle time. Though I'm actually unsure as to how to invoke into the command that's associated with the message that arrives off the queue.
To be more specific, if the command invocation needs to do service requests there's going to be latency in the invocation that could be used to get the next message. Stuff like that. I can totally do this simply by wrapping up things in queues and coordinating this myself but I'd like to see this work with just some async/await stuff.

While I could make most of my methods async I don't feel as if I have a basic understanding of when I'd must do this.
Start at the lowest level. It sounds like you've already got a start, but if you're looking for more at the lowest level, then the rule of thumb is anything I/O-based should be made async (e.g., HttpClient).
Then it's a matter of repeating the async infection. You want to use async methods, so you call them with await. So that method must be async. So all of its callers must use await, so they must also be async, etc.
how would I then invoke the first async method of my program if I built say a message loop where I want some control of the degree of parallelism?
It's easiest to put the framework in charge of this. E.g., you can just return a Task<T> from a WebAPI action, and the framework understands that. Similarly, UI applications have a message loop built-in that async will work naturally with.
If you have a situation where the framework doesn't understand Task or have a built-in message loop (usually a Console application or a Win32 service), you can use the AsyncContext type in my AsyncEx library. AsyncContext just installs a "main loop" (that is compatible with async) onto the current thread.
Since the HttpClient doesn't have any synchronous methods, what can I safely presume to do if I have an abstraction that isn't async aware?
The correct approach is to change the abstraction. Do not attempt to block on asynchronous code; I describe that common deadlock scenario in detail on my blog.
You change the abstraction by making it async-friendly. For example, change IUserContext IUserContextService.GetUserContext() to Task<IUserContext> IUserContextService.GetUserContextAsync().
I've read about the ConfigureAwait(false) but I don't really understand what it does. It's strange to me that it's set after the async invocation.
You may find my async intro helpful. I won't say much more about ConfigureAwait in this answer because I think it's not directly applicable to a good solution for this question (but I'm not saying it's bad; it actually should be used unless you can't use it).
Just bear in mind that async is an operator with precedence rules and all that. It feels magical at first, but it's really not so much. This code:
var result = await httpClient.GetAsync(url).ConfigureAwait(false);
is exactly the same as this code:
var asyncOperation = httpClient.GetAsync(url).ConfigureAwait(false);
var result = await asyncOperation;
There are usually no race conditions in async code because - even though the method is asynchronous - it is also sequential. The method can be paused at an await, and it will not be resumed until that await completes.
When you have a message loop that allow things to happen in parallel and you have asynchronous methods, there's a opportunity to minimize latency.
This is the second time you've mentioned a "message loop" "in parallel", but I think what you actually want is to have multiple (asynchronous) consumers working off the same queue, correct? That's easy enough to do with async (note that there is just a single message loop on a single thread in this example; when everything is async, that's usually all you need):
await tasks.WhenAll(ConsumerAsync(), ConsumerAsync(), ConsumerAsync());
async Task ConsumerAsync()
{
for (;;) // TODO: consider a CancellationToken for orderly shutdown
{
var m = await mq.ReceiveAsync();
var c = GetCommand(m);
await c.InvokeAsync();
m.Delete();
}
}
// Extension method
public static Task<Message> ReceiveAsync(this MessageQueue mq)
{
return Task<Message>.Factory.FromAsync(mq.BeginReceive, mq.EndReceive, null);
}
You'd probably also be interested in TPL Dataflow. Dataflow is a library that understands and works well with async code, and has nice parallel options built-in.

While I appreciate the insight from community members it's always difficult to express the intent of what I'm trying to do but tremendously helpful to get advice about circumstances surrounding the problem. With that, I eventually arrived that the following code.
public class AsyncOperatingContext
{
struct Continuation
{
private readonly SendOrPostCallback d;
private readonly object state;
public Continuation(SendOrPostCallback d, object state)
{
this.d = d;
this.state = state;
}
public void Run()
{
d(state);
}
}
class BlockingSynchronizationContext : SynchronizationContext
{
readonly BlockingCollection<Continuation> _workQueue;
public BlockingSynchronizationContext(BlockingCollection<Continuation> workQueue)
{
_workQueue = workQueue;
}
public override void Post(SendOrPostCallback d, object state)
{
_workQueue.TryAdd(new Continuation(d, state));
}
}
/// <summary>
/// Gets the recommended max degree of parallelism. (Your main program message loop could use this value.)
/// </summary>
public static int MaxDegreeOfParallelism { get { return Environment.ProcessorCount; } }
#region Helper methods
/// <summary>
/// Run an async task. This method will block execution (and use the calling thread as a worker thread) until the async task has completed.
/// </summary>
public static T Run<T>(Func<Task<T>> main, int degreeOfParallelism = 1)
{
var asyncOperatingContext = new AsyncOperatingContext();
asyncOperatingContext.DegreeOfParallelism = degreeOfParallelism;
return asyncOperatingContext.RunMain(main);
}
/// <summary>
/// Run an async task. This method will block execution (and use the calling thread as a worker thread) until the async task has completed.
/// </summary>
public static void Run(Func<Task> main, int degreeOfParallelism = 1)
{
var asyncOperatingContext = new AsyncOperatingContext();
asyncOperatingContext.DegreeOfParallelism = degreeOfParallelism;
asyncOperatingContext.RunMain(main);
}
#endregion
private readonly BlockingCollection<Continuation> _workQueue;
public int DegreeOfParallelism { get; set; }
public AsyncOperatingContext()
{
_workQueue = new BlockingCollection<Continuation>();
}
/// <summary>
/// Initialize the current thread's SynchronizationContext so that work is scheduled to run through this AsyncOperatingContext.
/// </summary>
protected void InitializeSynchronizationContext()
{
SynchronizationContext.SetSynchronizationContext(new BlockingSynchronizationContext(_workQueue));
}
protected void RunMessageLoop()
{
while (!_workQueue.IsCompleted)
{
Continuation continuation;
if (_workQueue.TryTake(out continuation, Timeout.Infinite))
{
continuation.Run();
}
}
}
protected T RunMain<T>(Func<Task<T>> main)
{
var degreeOfParallelism = DegreeOfParallelism;
if (!((1 <= degreeOfParallelism) & (degreeOfParallelism <= 5000))) // sanity check
{
throw new ArgumentOutOfRangeException("DegreeOfParallelism must be between 1 and 5000.", "DegreeOfParallelism");
}
var currentSynchronizationContext = SynchronizationContext.Current;
InitializeSynchronizationContext(); // must set SynchronizationContext before main() task is scheduled
var mainTask = main(); // schedule "main" task
mainTask.ContinueWith(task => _workQueue.CompleteAdding());
// for single threading we don't need worker threads so we don't use any
// otherwise (for increased parallelism) we simply launch X worker threads
if (degreeOfParallelism > 1)
{
for (int i = 1; i < degreeOfParallelism; i++)
{
ThreadPool.QueueUserWorkItem(_ => {
// do we really need to restore the SynchronizationContext here as well?
InitializeSynchronizationContext();
RunMessageLoop();
});
}
}
RunMessageLoop();
SynchronizationContext.SetSynchronizationContext(currentSynchronizationContext); // restore
return mainTask.Result;
}
protected void RunMain(Func<Task> main)
{
// The return value doesn't matter here
RunMain(async () => { await main(); return 0; });
}
}
This class is complete and it does a couple of things that I found difficult to grasp.
As general advice you should allow the TAP (task-based asynchronous) pattern to propagate through your code. This may imply quite a bit of refactoring (or redesign). Ideally you should be allowed to break this up into pieces and make progress as you work towards to overall goal of making your program more asynchronous.
Something that's inherently dangerous to do is to call asynchronous code callously in an synchronous fashion. By this we mean invoking the Wait or Result methods. These can lead to deadlocks. One way to work around something like that is to use the AsyncOperatingContext.Run method. It will use the current thread to run a message loop until the asynchronous call is complete. It will swap out whatever SynchronizationContext is associated with the current thread temporarily to do so.
Note: I don't know if this is enough, or if you are allowed to swap back the SynchronizationContext this way, assuming that you can, this should work. I've already been bitten by the ASP.NET deadlock issue and this could possibly function as a workaround.
Lastly, I found myself asking the question, what is the corresponding equivalent of Main(string[]) in an async context? Turns out that's the message loop.
What I've found is that there are two things that make out this async machinery.
SynchronizationContext.Post and the message loop. In my AsyncOperatingContext I provide a very simple message loop:
protected void RunMessageLoop()
{
while (!_workQueue.IsCompleted)
{
Continuation continuation;
if (_workQueue.TryTake(out continuation, Timeout.Infinite))
{
continuation.Run();
}
}
}
My SynchronizationContext.Post thus becomes:
public override void Post(SendOrPostCallback d, object state)
{
_workQueue.TryAdd(new Continuation(d, state));
}
And our entry point, basically the equivalent of an async main from synchronous context (simplified version from original source):
SynchronizationContext.SetSynchronizationContext(new BlockingSynchronizationContext(_workQueue));
var mainTask = main(); // schedule "main" task
mainTask.ContinueWith(task => _workQueue.CompleteAdding());
RunMessageLoop();
return mainTask.Result;
All of this is costly and we can't just go replace calls to async methods with this but it does allow us to rather quickly create the facilities required to keep writing async code where needed without having to deal with the whole program. It's also very clear from this implementation where the worker threads go and how the impact concurrency of your program.
I look at this and think to myself, yeap, that's how Node.js does it. Though JavaScript does not have this nice async/await language support that C# currently does.
As an added bonus, I have complete control of the degree of parallelism, and if I want, I can run my async tasks completely single threaded. Though, If I do so and call Wait or Result on any task, it will deadlock the program because it will block the only message loop available.

How to return type of Task<mytype> without running async

In my data access layer I'm attempting to create methods with return types of Task.
I cannot get the return type from the entity framework to return Task<List<MYtype>>
public static Task<List<ILeaf>> GetLeafs(int doorID)
{
using (var db = new StorefrontSystemEntities())
{
return db.proc_GetDoorLeafs(doorID).ToList<ILeaf>();
};
}
Is the only way to make this run correctly is to format the code like so:
public async static Task<List<ILeaf>> GetLeafs(int doorID)
{
return await Task.Run(() =>
{
using (var db = new StorefrontSystemEntities())
{
return db.proc_GetDoorLeafs(doorID).ToList<ILeaf>();
};
});
}
The reason I was asking is because I would like to give the option to run async, or am I not understanding this correctly?
If I can just return a Task then on the calling end I could give the option to await if I wanted to run async, but if i wanted to run synchronously I would just call the method as normal.
If I'm returning a Task do I always have to include the async keyword in the method signature?
Am I thinking about this the wrong way? If I've got a return type of Task then the method has the option of being called async or synchronously?
But, if I have async and Task in the method signature then the method runs async no matter what?
Thanks!

So to answer the literal question asked, you can just do this:
public static Task<List<ILeaf>> GetLeafs(int doorID)
{
return Task.Run(() =>
{
using (var db = new StorefrontSystemEntities())
{
return db.proc_GetDoorLeafs(doorID).ToList<ILeaf>();
};
});
}
That said, note that this isn't a particularly useful method. The idea of leveraging asynchronous programming is that you don't want to have a thread pool thread sitting there doing nothing but waiting on this IO operation. Ideally you'd leverage IO that is inherently asynchronous in nature; a method that itself naturally returns a task.
You aren't really providing value to consumers of your code by wrapping the blocking IO in a call to Task.Run. If they need that operation to be run in a background thread they can do so on their own, and then they'll know more precisely that it's not a naively asynchronous operation.
See Should I expose asynchronous wrappers for synchronous methods? for more information on the subject.

public static async Task<List<ILeaf>> GetLeafs(int doorID)
{
using (var db = new StorefrontSystemEntities())
{
var result = db.proc_GetDoorLeafs(doorID).ToList<ILeaf>();
return await Task.FromResult(result);
}
}

How to safely call an async method in C# without await

I have an async method which returns no data:
public async Task MyAsyncMethod()
{
// do some stuff async, don't return any data
}
I'm calling this from another method which returns some data:
public string GetStringData()
{
MyAsyncMethod(); // this generates a warning and swallows exceptions
return "hello world";
}
Calling MyAsyncMethod() without awaiting it causes a "Because this call is not awaited, the current method continues to run before the call is completed" warning in visual studio. On the page for that warning it states:
You should consider suppressing the warning only if you're sure that you don't want to wait for the asynchronous call to complete and that the called method won't raise any exceptions.
I'm sure I don't want to wait for the call to complete; I don't need to or have the time to. But the call might raise exceptions.
I've stumbled into this problem a few times and I'm sure it's a common problem which must have a common solution.
How do I safely call an async method without awaiting the result?
Update:
For people suggesting that I just await the result, this is code that is responding to a web request on our web service (ASP.NET Web API). Awaiting in a UI context keeps the UI thread free, but awaiting in a web request call will wait for the Task to finish before responding to the request, thereby increasing response times with no reason.

If you want to get the exception "asynchronously", you could do:
MyAsyncMethod().
ContinueWith(t => Console.WriteLine(t.Exception),
TaskContinuationOptions.OnlyOnFaulted);
This will allow you to deal with an exception on a thread other than the "main" thread. This means you don't have to "wait" for the call to MyAsyncMethod() from the thread that calls MyAsyncMethod; but, still allows you to do something with an exception--but only if an exception occurs.
Update:
technically, you could do something similar with await:
try
{
await MyAsyncMethod().ConfigureAwait(false);
}
catch (Exception ex)
{
Trace.WriteLine(ex);
}
...which would be useful if you needed to specifically use try/catch (or using) but I find the ContinueWith to be a little more explicit because you have to know what ConfigureAwait(false) means.

You should first consider making GetStringData an async method and have it await the task returned from MyAsyncMethod.
If you're absolutely sure that you don't need to handle exceptions from MyAsyncMethod or know when it completes, then you can do this:
public string GetStringData()
{
var _ = MyAsyncMethod();
return "hello world";
}
BTW, this is not a "common problem". It's very rare to want to execute some code and not care whether it completes and not care whether it completes successfully.
Update:
Since you're on ASP.NET and wanting to return early, you may find my blog post on the subject useful. However, ASP.NET was not designed for this, and there's no guarantee that your code will run after the response is returned. ASP.NET will do its best to let it run, but it can't guarantee it.
So, this is a fine solution for something simple like tossing an event into a log where it doesn't really matter if you lose a few here and there. It's not a good solution for any kind of business-critical operations. In those situations, you must adopt a more complex architecture, with a persistent way to save the operations (e.g., Azure Queues, MSMQ) and a separate background process (e.g., Azure Worker Role, Win32 Service) to process them.

The answer by Peter Ritchie was what I wanted, and Stephen Cleary's article about returning early in ASP.NET was very helpful.
As a more general problem however (not specific to an ASP.NET context) the following Console application demonstrates the usage and behavior of Peter's answer using Task.ContinueWith(...)
static void Main(string[] args)
{
try
{
// output "hello world" as method returns early
Console.WriteLine(GetStringData());
}
catch
{
// Exception is NOT caught here
}
Console.ReadLine();
}
public static string GetStringData()
{
MyAsyncMethod().ContinueWith(OnMyAsyncMethodFailed, TaskContinuationOptions.OnlyOnFaulted);
return "hello world";
}
public static async Task MyAsyncMethod()
{
await Task.Run(() => { throw new Exception("thrown on background thread"); });
}
public static void OnMyAsyncMethodFailed(Task task)
{
Exception ex = task.Exception;
// Deal with exceptions here however you want
}
GetStringData() returns early without awaiting MyAsyncMethod() and exceptions thrown in MyAsyncMethod() are dealt with in OnMyAsyncMethodFailed(Task task) and not in the try/catch around GetStringData()

I end up with this solution :
public async Task MyAsyncMethod()
{
// do some stuff async, don't return any data
}
public string GetStringData()
{
// Run async, no warning, exception are catched
RunAsync(MyAsyncMethod());
return "hello world";
}
private void RunAsync(Task task)
{
task.ContinueWith(t =>
{
ILog log = ServiceLocator.Current.GetInstance<ILog>();
log.Error("Unexpected Error", t.Exception);
}, TaskContinuationOptions.OnlyOnFaulted);
}

This is called fire and forget, and there is an extension for that.
Consumes a task and doesn't do anything with it. Useful for fire-and-forget calls to async methods within async methods.
Install nuget package.
Use:
MyAsyncMethod().Forget();
EDIT: There is another way I've been rather using lately:
_ = MyAsyncMethod();

Not the best practice, you should try avoiding this.
However, just to address "Call an async method in C# without await", you can execute the async method inside a Task.Run. This approach will wait until MyAsyncMethod finish.
public string GetStringData()
{
Task.Run(()=> MyAsyncMethod()).Result;
return "hello world";
}
await asynchronously unwraps the Result of your task, whereas just using Result would block until the task had completed.
If you want to wrap it in a helper class:
public static class AsyncHelper
{
public static void Sync(Func<Task> func) => Task.Run(func).ConfigureAwait(false);
public static T Sync<T>(Func<Task<T>> func) => Task.Run(func).Result;
}
and call like
public string GetStringData()
{
AsyncHelper.Sync(() => MyAsyncMethod());
return "hello world";
}

I'm late to the party here, but there's an awesome library I've been using which I haven't seen referenced in the other answers
https://github.com/brminnick/AsyncAwaitBestPractices
If you need to "Fire And Forget" you call the extension method on the task.
Passing the action onException to the call ensures that you get the best of both worlds - no need to await execution and slow your users down, whilst retaining the ability to handle the exception in a graceful manner.
In your example you would use it like this:
public string GetStringData()
{
MyAsyncMethod().SafeFireAndForget(onException: (exception) =>
{
//DO STUFF WITH THE EXCEPTION
});
return "hello world";
}
It also gives awaitable AsyncCommands implementing ICommand out the box which is great for my MVVM Xamarin solution

Typically async method returns Task class. If you use Wait() method or Result property and code throws exception - exception type gets wrapped up into AggregateException - then you need to query Exception.InnerException to locate correct exception.
But it's also possible to use .GetAwaiter().GetResult() instead -
it will also wait async task, but will not wrap exception.
So here is short example:
public async Task MyMethodAsync()
{
}
public string GetStringData()
{
MyMethodAsync().GetAwaiter().GetResult();
return "test";
}
You might want also to be able to return some parameter from async function - that can be achieved by providing extra Action<return type> into async function, for example like this:
public string GetStringData()
{
return MyMethodWithReturnParameterAsync().GetAwaiter().GetResult();
}
public async Task<String> MyMethodWithReturnParameterAsync()
{
return "test";
}
Please note that async methods typically have ASync suffix naming, just to be able to avoid collision between sync functions with same name. (E.g. FileStream.ReadAsync) - I have updated function names to follow this recommendation.

I guess the question arises, why would you need to do this? The reason for async in C# 5.0 is so you can await a result. This method is not actually asynchronous, but simply called at a time so as not to interfere too much with the current thread.
Perhaps it may be better to start a thread and leave it to finish on its own.

On technologies with message loops (not sure if ASP is one of them), you can block the loop and process messages until the task is over, and use ContinueWith to unblock the code:
public void WaitForTask(Task task)
{
DispatcherFrame frame = new DispatcherFrame();
task.ContinueWith(t => frame.Continue = false));
Dispatcher.PushFrame(frame);
}
This approach is similar to blocking on ShowDialog and still keeping the UI responsive.

Maybe I'm too naive but, couldn't you create an event that is raised when GetStringData() is called and attach an EventHandler that calls and awaits the async method?
Something like:
public event EventHandler FireAsync;
public string GetStringData()
{
FireAsync?.Invoke(this, EventArgs.Empty);
return "hello world";
}
public async void HandleFireAsync(object sender, EventArgs e)
{
await MyAsyncMethod();
}
And somewhere in the code attach and detach from the event:
FireAsync += HandleFireAsync;
(...)
FireAsync -= HandleFireAsync;
Not sure if this might be anti-pattern somehow (if it is please let me know), but it catches the Exceptions and returns quickly from GetStringData().

The solution is start the HttpClient into another execution task without sincronization context:
var submit = httpClient.PostAsync(uri, new StringContent(body, Encoding.UTF8,"application/json"));
var t = Task.Run(() => submit.ConfigureAwait(false));
await t.ConfigureAwait(false);

It is straightforward, just call asyncMethod().Result to call without await. Below is the sample code and here is the fiddle
using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
var asyncDemo = new AsyncDemo();
asyncDemo.TestMethod1Void().Wait();
var result = asyncDemo.TestMethod1().Result;
Console.WriteLine(result);
}
}
public class AsyncDemo {
public async Task<string> TestMethod1()
{
Thread.Sleep(1000);
return "From Async Method";
}
public async Task TestMethod1Void()
{
Thread.Sleep(1000);
Console.WriteLine("Async Void Method");
}
}