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Keep Task and Task.FromResult if method is synchronous or remove Task-stuff at all?

I have a Web API controller (ASP.NET Core 5). Some of my APIs are asynchronous and some of them not. My question is next: Is there any advantages of using public **Task<T>** WebApiMethod + Task.FromResult() in Web API controllers if my method is synchronous?
For example:
public Task<string> GetSomeData()
{
// some synchronous processing...
return Task.FromResult(result);
}
Should I turn the example code above to something like this?
public string GetSomeData()
{
// some synchronous processing...
return result;
}

If the api is doing synchronous work it should have a synchronous signature. it will make the readability and understanding of the function clearer to other developers and will prevent misunderstanding when reading this function again in the future.
In the future, if the method will need to be modified to have an asynchronous task to do, you can change the signature to have an asynchronous signature.

You should use synchronous methods if the work is synchronous.
Yet, you should use Task signatures if you use some form of caching (e.g. with the proxy pattern). Then, of course if you already did the expensive I/O work, use Task.FromResult to return the cached result, and return the I/O task if it has to be newly downloaded.

It shouldn't have much difference in the way it is executed. If you can make the processing part asynchronous then it would make some difference.

Handling synchronous methods in async/await best practices (turtles all the way down)

With async turtles all the way down ...
Some of the background research:
Async/Await - Best Practices in Asynchronous Programming
Async
In code I've seen:
Developers wrap code in a Task.Run() upon entering a method and awaiting it to force it to be async or (or older .NET 4.0 TaskFactory.StartNew())
I've personally just left it synchronous (but it partially violates turtles all the down as different branches often are sync)
I've also seen the attempt to use ValueTask to short-circuit the return as async given the nature of ValueTask with a return value being akin to:
return new ValueTask<int>(valueWantToReturn);
Example psudeo code:
public async Task ParentMethodAsync()
{
// ... do something upon entering
int neededValue = SyncNestedDryMethod(); // ** this part **
await _nthLayer.DoSomethingWithRepoAsync(); // ** same concept applies here
// if there is no asyncronous logic required **
// ... do anything else needed
}
public int SyncNestedDryMethod()
{
// ... do something that requires no real async method signature
// declaration because it is straight synchronous logic (covers reusing
// code for DRY purposes, method-level SRP abstraction (includes moving it
// to an abstracted class -- for future readers), etc.)
// I've seen making the method async then awaiting Task.Run() or
// Task.StartFactory.New() inside this (sync changed to async method)
// to try and force it to be async or last line being:
// return new ValueTask<int>(valueWantToReturn);
// but everything above it being only syncronous logic
}
Is there a best practice to be aware of not found addressed in the respective links (or overlooked) or elsewhere which I have not come across to address abstracting synchronous code into new methods (for DRY purposes, SRP, etc.) that do not have the ability to be async or are forced async all the while following async through and through?

Your question isn't entirely clear, but I think you're asking how to run synchronous code in an asynchronous way? If so, the answer is: you can't.
Using Task.Run() doesn't make the code asynchronous. It just runs the code on a different thread and gives you an asynchronous way to wait for that thread to complete. That may be what you need if you just need to get the work off of the current thread. For example, you would use that in a desktop application where you want to get the work off of the UI thread. But this wouldn't help you at all in ASP.NET.
ValueTask is used for cases where the work might be done asynchronously, but also may complete synchronously too. For example, if data is usually returned from an in memory cache, but refreshing that cache is done asynchronously. This is described in detail here. But if the work is always synchronous, then there is no point using ValueTask, or Task or async.

C# Async when also needing support for synchronous call

I'm in a situation where we have some code that is run by user input (button click), that runs through a series of function calls and result in generating some data (which is a quite heavy operation, several minutes). We'd like to use Async for this so that it doesn't lock up the UI while we're doing this operation.
But at the same time we also have a requirement that the functions will also be available through an API which preferably should be synchronous.
Visualization/Example (pseudo-code):
public async void Button_Click() // from UI context
{
await instanceOfClassA.FuncA();
// some code
}
public async Task ClassA.FuncA()
{
await instanceOfClassB.FuncB()
// some code
}
public async Task ClassB.FuncB()
{
await instanceOfClassC.SomeHeavyFunc()
// some code
}
public async Task ClassC.SomeHeavyFunc()
{
// some heavy calculations
}
// Also need to provide a public synchronous API function
public void SomeClass.SynchronousAPIFunc()
{
// need to call differentInstanceOfClassB.FuncB()
}
Is there a way to make it so that the public API function does the waiting for the async operation internally?
EDIT:
In this post, user Rachel provides two answers to the question. Both seem interesting, though I'm unsure which one would offer the least amount of risk/side effects.
EDIT2:
I should note that we're using .NET v4.6.1.
Thanks in advance.

The problem with making "synchronous" versions of your methods that just call the asynchronous versions is that it can cause deadlocks, especially if the person calling this code is not aware that this is what is happening.
If you really want to make synchronous versions, then follow Microsoft's lead and write completely new methods that do not use any asynchronous code. For example, the implementation for File.ReadAllLines() doesn't use any of the same code as File.ReadAllLinesAsync().
If you don't want to do that, then just don't provide synchronous versions of your methods. Let the caller make the decision on how to deal with it. If they want to block synchronously on it, then they can mitigate the risk of deadlock.

But at the same time we also have a requirement that the functions will also be available through an API which preferably should be synchronous.
If you have the need to expose both a synchronous and asynchronous API, I recommend the boolean argument hack. This looks like:
public Task<T> FuncBAsync() => FuncBAsync(sync: false);
public T FuncB() => FuncBAsync(sync: true).GetAwaiter().GetResult();
public async Task<T> FuncBAsync(bool sync)
{
// Note: is `sync` is `true`, this method ***must*** return a completed task.
...
}
Is there a way to make it so that the public API function does the waiting for the async operation internally?
I do not recommend using direct blocking (e.g., GetAwaiter().GetResult()), as the straightforward implementation will lead to deadlocks.
EDIT: In this post, user Rachel provides two answers to the question.
I strongly recommend against using that solution. It uses a nested message loop with a custom SynchronizationContext, but doesn't do COM pumping. This can cause problems particularly if called from a UI thread. Even if the pumping isn't a problem, this solution can cause unexpected re-entrancy, which is a source of countless, extremely subtle, and difficult-to-find bugs.

You can utilize .GetAwaiter().GetResult()
as per your example, it would look like:
public void SomeClass.SynchronousAPIFunc()
{
// need to call differentInstanceOfClassB.FuncB()
ClassB.FuncB().GetAwaiter().GetResult();
}
Also, a good reference on when to not use the above can be found at Dont Block on Async Code

Async-await - Am I over doing it?

Recently I've developed doubts about the way I'm implementing the async-await pattern in my Web API projects. I've read that async-await should be "all the way" and that's what I've done. But it's all starting to seem redundant and I'm not sure that I'm doing this correctly. I've a got a controller that calls a repository and it calls a data access (entity framework 6) class - "async all the way". I've read a lot of conflicting stuff on this and would like to get it cleared-up.
EDIT: The referenced possible duplicate is a good post, but not specific enough for my needs. I included code to illustrate the problem. It seems really difficult to get a decisive answer on this. It would be nice if we could put async-await in one place and let .net handle the rest, but we can't. So, am I over doing it or is it not that simple.
Here's what I've got:
Controller:
public async Task<IHttpActionResult> GetMessages()
{
var result = await _messageRepository.GetMessagesAsync().ConfigureAwait(false);
return Ok(result);
}
Repository:
public async Task<List<string>> GetMessagesAsync()
{
return await _referralMessageData.GetMessagesAsync().ConfigureAwait(false);
}
Data:
public async Task<List<string>> GetMessagesAsync()
{
return await _context.Messages.Select(i => i.Message).ToListAsync().ConfigureAwait(false);
}

It would be nice if we could put async-await in one place and let .net handle the rest, but we can't. So, am I over doing it or is it not that simple.
It would be nice if it was simpler.
The sample repository and data code don't have much real logic in them (and none after the await), so they can be simplified to return the tasks directly, as other commenters have noted.
On a side note, the sample repository suffers from a common repository problem: doing nothing. If the rest of your real-world repository is similar, you might have one level of abstraction too many in your system. Note that Entity Framework is already a generic unit-of-work repository.
But regarding async and await in the general case, the code often has work to do after the await:
public async Task<IHttpActionResult> GetMessages()
{
var result = await _messageRepository.GetMessagesAsync();
return Ok(result);
}
Remember that async and await are just fancy syntax for hooking up callbacks. There isn't an easier way to express this method's logic asynchronously. There have been some experiments around, e.g., inferring await, but they have all been discarded at this point (I have a blog post describing why the async/await keywords have all the "cruft" that they do).
And this cruft is necessary for each method. Each method using async/await is establishing its own callback. If the callback isn't necessary, then the method can just return the task directly, avoiding async/await. Other asynchronous systems (e.g., promises in JavaScript) have the same restriction: they have to be asynchronous all the way.
It's possible - conceptually - to define a system in which any blocking operation would yield the thread automatically. My foremost argument against a system like this is that it would have implicit reentrancy. Particularly when considering third-party library changes, an auto-yielding system would be unmaintainable IMO. It's far better to have the asynchrony of an API explicit in its signature (i.e., if it returns Task, then it's asynchronous).
Now, #usr makes a good point that maybe you don't need asynchrony at all. That's almost certainly true if, e.g., your Entity Framework code is querying a single instance of SQL Server. This is because the primary benefit of async on ASP.NET is scalability, and if you don't need scalability (of the ASP.NET portion), then you don't need asynchrony. See the "not a silver bullet" section in my MSDN article on async ASP.NET.
However, I think there's also an argument to be made for "natural APIs". If an operation is naturally asynchronous (e.g., I/O-based), then its most natural API is an asynchronous API. Conversely, naturally synchronous operations (e.g., CPU-based) are most naturally represented as synchronous APIs. The natural API argument is strongest for libraries - if your repository / data access layer was its own dll intended to be reused in other (possibly desktop or mobile) applications, then it should definitely be an asynchronous API. But if (as is more likely the case) it is specific to this ASP.NET application which does not need to scale, then there's no specific need to make the API either asynchronous or synchronous.
But there's a good two-pronged counter-argument regarding developer experience. Many developers don't know their way around async at all; would a code maintainer be likely to mess it up? The other prong of that argument is that the libraries and tooling around async are still coming up to speed. Most notable is the lack of a causality stack when there are exceptions to trace down (on a side note, I wrote a library that helps with this). Furthermore, parts of ASP.NET are not async-compatible - most notably, MVC filters and child actions (they are fixing both of those with ASP.NET vNext). And ASP.NET has different behavior regarding timeouts and thread aborts for asynchronous handlers - adding yet a little more to the async learning curve.
Of course, the counter-counter argument would be that the proper response to behind-the-times developers is to train them, not restrict the technologies available.
In short:
The proper way to do async is "all the way". This is especially true on ASP.NET, and it's not likely to change anytime soon.
Whether async is appropriate, or helpful, is up to you and your application's scenario.

public async Task<List<string>> GetMessagesAsync()
{
return await _referralMessageData.GetMessagesAsync().ConfigureAwait(false);
}
public async Task<List<string>> GetMessagesAsync()
{
return await _context.Messages.Select(i => i.Message).ToListAsync().ConfigureAwait(false);
}
If the only calls you do to asynchronous methods are tail-calls, then you don't really need to await:
public Task<List<string>> GetMessagesAsync()
{
return _referralMessageData.GetMessagesAsync();
}
public Task<List<string>> GetMessagesAsync()
{
return _context.Messages.Select(i => i.Message).ToListAsync();
}
About the only thing you lose is some stack-trace information, but that's rarely all that useful. Remove the await then instead of generating a state-machine that handles the waiting you just pass back the task produced by the called method up to the calling method, and the calling method can await on that.
The methods can also sometimes be inlined now, or perhaps have tail-call optimisation done on them.
I'd even go so far as to turn non-task-based paths into task-based if it was relatively simple to do so:
public async Task<List<string>> GetMeesagesAsync()
{
if(messageCache != null)
return messageCache;
return await _referralMessageData.GetMessagesAsync().ConfigureAwait(false);
}
Becomes:
public Task<List<string>> GetMeesagesAsync()
{
if(messageCache != null)
return Task.FromResult(messageCache);
return _referralMessageData.GetMessagesAsync();
}
However, if at any point you need the results of a task to do further work, then awaiting is the way to go.

How do I fix this deadlock in Win Forms constructor when using async/await?

Here is my minimum repro case:
public Form1()
{
Task.Delay(100).Wait(); // Works just fine
this.Await().Wait(); // Blocks indefinitely
}
private async Task Await()
{
await Task.Delay(100);
}
What is going on here? Why are these two behaving differently? What can I do to make the later one work?
My actual case is less trivial, and I can't "just use the first option".

You're seeing a classic deadlock situation that I describe on my blog and in an MSDN article. In short, after the await completes, the async method is attempting to resume on the UI thread, which you have blocked by calling Wait.
To fix it, you ideally want to use async all the way (i.e., never block on async code). Constructors pose a difficulty here (since they cannot be async); I explore several options on my blog. The correct option depends on your code base, but I recommend the async factory method if possible. The options are:
Async factory method.
Asynchronous lazy initialization.
Asynchronous initialization pattern.
If you absolutely cannot use one of the options that I describe on my blog, then you can work around this by using ConfigureAwait(false) in all your async methods, and then your Wait() will not deadlock. However, this will block the UI thread during those asynchronous method calls (which sort of defeats the purpose of them being async in the first place...)