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Implementing both IDisposable and IAsyncDisposable

Say I have a non-sealed class that does not deal with any unmanaged resources. I need to make a single async call during its disposing stage to do some clean up. There are no other managed resources to deal with.
From what I understand, in order to make the async clean up call, I must implement IAsyncDisposable and use the DisposeAsync() and DisposeAsyncCore() methods. But the guidance says that you should also implement the dispose pattern when you implement the async dispose pattern. This is all fine but there's nothing really I need to do in the Dispose().
So my question is, should the Dispose() logic be empty or do I need something to do the async cleanup in a synchronous way? (see comment in code about "What if anything should go here").
public class MyClass : IDisposable, IAsyncDisposable
{
private bool disposed;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
public async ValueTask DisposeAsync()
{
await DisposeAsyncCore().ConfigureAwait(false);
Dispose(false);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
if (disposing)
{
// What if anything should go here?
}
disposed = true;
}
}
protected virtual async ValueTask DisposeAsyncCore()
{
// Make async cleanup call here e.g. Database.CleanupAsync();
}
}

Example to those who still hesitate to implement both:
internal class Program
{
static void Main(string[] args)
{
foreach (var a in new B()){}
//IAsyncDisposable is not called - you leaking resources.
//No deadlocks in UI, no warning in compilation, nothing.
//So it is better to be on safe side and implement both
//because you never know how one will manage lifetime of your class.
}
public class B : IEnumerable, IAsyncEnumerable<object>
{
public IEnumerator GetEnumerator() => new A();
public IAsyncEnumerator<object> GetAsyncEnumerator(CancellationToken ct) => new A();
}
public class A : IAsyncEnumerator<object>, IEnumerator
{
public ValueTask DisposeAsync()
{
Console.WriteLine("Async Disposed");
return ValueTask.CompletedTask;
}
public bool MoveNext() => false;
public void Reset(){}
public ValueTask<bool> MoveNextAsync() => ValueTask.FromResult(false);
public object Current => null;
}
}
Conclusion
You can freely add support for async version only, but beware: some wraps, like foreach or older versions of DI containers (Ninject, StructureMap, etc), code generators like RestSharp, or proxy generators like Castle.Proxy might not support IAsyncDisposable. Failing to cast object to IDisposable will present hard to catch bugs in your app. Whereas if you do implement it, the worst thing that could happen is deadlock in finally block (if you do it through sync-over-async).
In general, it is better to support both operations if you plan to make it public API or you don't have control over your class lifetime (like in DI containers or other widely known wrappers).
How to
There is full Microsoft example on how to implement both of them in inheritable class (non-sealed, like in your example) - https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/implementing-disposeasync#implement-both-dispose-and-async-dispose-patterns
class ExampleConjunctiveDisposableusing : IDisposable, IAsyncDisposable
{
IDisposable? _disposableResource = new MemoryStream();
IAsyncDisposable? _asyncDisposableResource = new MemoryStream();
public void Dispose()
{
Dispose(disposing: true);
GC.SuppressFinalize(this);
}
public async ValueTask DisposeAsync()
{
await DisposeAsyncCore().ConfigureAwait(false);
Dispose(disposing: false);
#pragma warning disable CA1816 // Dispose methods should call SuppressFinalize
GC.SuppressFinalize(this);
#pragma warning restore CA1816 // Dispose methods should call SuppressFinalize
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
_disposableResource?.Dispose();
(_asyncDisposableResource as IDisposable)?.Dispose();
_disposableResource = null;
_asyncDisposableResource = null;
}
}
protected virtual async ValueTask DisposeAsyncCore()
{
if (_asyncDisposableResource is not null)
{
await _asyncDisposableResource.DisposeAsync().ConfigureAwait(false);
}
if (_disposableResource is IAsyncDisposable disposable)
{
await disposable.DisposeAsync().ConfigureAwait(false);
}
else
{
_disposableResource?.Dispose();
}
_asyncDisposableResource = null;
_disposableResource = null;
}
}

Both implementations of dispose feature is from the callers point of view. Your class would then offer both mechanisms to dispose off any managed and unmanaged resources and the caller application decides what to choose. This also ensures that any consumer which is unable to make use of asynchronous patterns are not lost.
You do not really need to implement synchronous dispose if you are sure about or want to force asynchronous consumption of your class.
So depending on your vision of class usage, you can choose how to dispose objects. If you choose to keep both mechanisms, you can dispose all resources both ways.

As you have said, the class is non-sealed. For sealed classes, it's enough to implement I(Async)Disposable interface. The Disposable pattern exists because the derived class may want to add cleanup logic that can be either sync or async. You can't know. That's why you need to implement the whole pattern for sync and async cases.
For your question. Never block async call in sync Dispose method. It's a caller's responsibility to use your class correctly. If he decides to call Dispose instead of DisposeAsync and clear only sync resources it's his decision/mistake. If this async call in DisposeAsync is absolutely necessary for proper cleanup and it is controlled by you, consider adding sync equivalent to be used in Dispose method.

How to properly dispose third party object (TelegramBotClient) in C#

I am using TelegramBotClient component in my project. Unfortunately the component
does not suggest any Dispose() method.
In my project I need to renew the object based on the token provided:
public TelegramBotClient NewClient(string token)
{
return new TelegramBotClient(token);
}
I need to dispose the object created
NewClient(token).SendTextMessageAsync(message.Chat.Id, message.Text, replyMarkup: keyboard, parseMode: Telegram.Bot.Types.Enums.ParseMode.Html);
How can I properly dispose the object?

If the third party-class implements IDisposable interface, then you can create object of that class with using block. This way the object disposal will be taken care by the framework.
If the class does not implements IDisposable that means that the class does not use any unmanaged resources and the author of the class does not see any possibility of memory leak caused by this class object if it not disposed intentionally.
If you still want to make sure that the third-party class object release the resources as soon at its usage is over, you can do that manually by wrapping it in your own class which implement IDisposable.
public class TextMessageClient : IDisposable
{
bool disposed = false;
private Telegram.Bot.TelegramBotClient client;
public TextMessageClient()
{
//Write your own logic to get the token
//Or accept the token as an argument of constructor.
var token = Guid.NewGuid().ToString();
client = new Telegram.Bot.TelegramBotClient(token);
}
public TextMessageClient(string token)
{
client = new Telegram.Bot.TelegramBotClient(token);
}
public async Task<Telegram.Bot.Types.Message> SendMessageAsync(string chatId, string message, string, IReplyMarkup keyboard, )
{
return await client.SendMessageAsync(chatId, message, replyMarkup: keyboard, parseMode: Telegram.Bot.Types.Enums.ParseMode.Html);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
// Protected implementation of Dispose pattern.
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing)
{
client = null;
}
disposed = true;
}
}
Now you can use this class as following.
using(var messageClient = new TextMessageClient())
{
var message = await messageClient.SendMessageAsync(<somechatid>, <somemessage>, <somerelaymarkup>);
}
I hope this will help you resolve your issue.

What's the recommended way to deal with leaked IAsyncDisposable instances?

I've been familiarizing myself with some of the things (that are planned to be) added in C# 8 & .NET Core 3.0, and am unsure on the correct way to implement IAsyncDisposable (at time of writing, this link has literally no guidance).
In particular, it is unclear to me what to do in the case when an instance isn't explicitly disposed - that is, it isn't wrapped in an async using(...) and .DisposeAsync() isn't explicitly called.
My first thought was to do that same thing I'd do when implementing IDisposable:
My DisposeAsync() implementation calls a DisposeAsync(bool disposing) with disposing: true
Implement a finalizer (with ~MyType()) that calls DisposeAsync(disposing: false)
DisposeAsync(bool disposing) actually frees and/or disposes everything, and suppresses finalizing if disposing == true.
My concerns are that there's nothing to await the results of DisposeAsync(bool) in the finalizer, and explicitly waiting in a finalizer seems really really dangerous.
Of course "just leak" also seems less than ideal.
To make this concrete, here's a (simplified) example class that does have a finalizer:
internal sealed class TestAsyncReader: IAsyncDisposable
{
private bool IsDisposed => Inner == null;
private TextReader Inner;
internal TestAsyncReader(TextReader inner)
{
Inner = inner;
}
// the question is, should this exist?
~TestAsyncReader()
{
DisposeAsync(disposing: false);
}
private ValueTask DisposeAsync(bool disposing)
{
// double dispose is legal, but try and do nothing anyway
if (IsDisposed)
{
return default;
}
// should a finalizer even exist?
if (disposing)
{
GC.SuppressFinalize(this);
}
// in real code some resources explicitly implement IAsyncDisposable,
// but for illustration purposes this code has an interface test
if (Inner is IAsyncDisposable supportsAsync)
{
var ret = supportsAsync.DisposeAsync();
Inner = null;
return ret;
}
// dispose synchronously, which is uninteresting
Inner.Dispose();
Inner = null;
return default;
}
public ValueTask DisposeAsync()
=> DisposeAsync(disposing: true);
}
So, is there any guidance around proper handling of leaked IAsyncDisposable instances?

Basing on examples of how it's implemented inside .NET Core classes (like here) and some recommendations from there, I'd say that when you need to implement IAsyncDisposable, the good practice would be to implement both IAsyncDisposable and IDisposable. In this case IAsyncDisposable will be only responsible for explicit scenarios when asyncronus disposal is needed, while IDisposable is supposed to be implemented as usual according to disposable pattern practices and it's going to serve all fallback scenarios including those when things come to finalization. Thus you don't need to have anything like DisposeAsync(bool disposing) - the asynchronous disposal cannot and shouldn't happen in a finalizer. The only bad news that you'll have to support both paths for resources reclaiming (synchronous and asynchronous).

Microsoft released their own guidance regarding this problem.
As in the accepted answer you should implement both interfaces
If you implement the IAsyncDisposable interface but not the IDisposable interface, your app can potentially leak resources. If a class implements IAsyncDisposable, but not IDisposable, and a consumer only calls Dispose, your implementation would never call DisposeAsync. This would result in a resource leak.
But also you may need to implement 2 dispose patterns:
using System;
using System.IO;
using System.Threading.Tasks;
class ExampleConjunctiveDisposableusing : IDisposable, IAsyncDisposable
{
IDisposable? _disposableResource = new MemoryStream();
IAsyncDisposable? _asyncDisposableResource = new MemoryStream();
public void Dispose()
{
Dispose(disposing: true);
GC.SuppressFinalize(this);
}
public async ValueTask DisposeAsync()
{
await DisposeAsyncCore().ConfigureAwait(false);
Dispose(disposing: false);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
_disposableResource?.Dispose();
(_asyncDisposableResource as IDisposable)?.Dispose();
_disposableResource = null;
_asyncDisposableResource = null;
}
}
protected virtual async ValueTask DisposeAsyncCore()
{
if (_asyncDisposableResource is not null)
{
await _asyncDisposableResource.DisposeAsync();
}
if (_disposableResource is IAsyncDisposable disposable)
{
await disposable.DisposeAsync();
}
else
{
_disposableResource?.Dispose();
}
_asyncDisposableResource = null;
_disposableResource = null;
}
}

Should I implement IDisposable when class has IDisposable member but no unmanaged resources?

The MSDN documentation and many answers here on StackOverflow go to lengths to disucss correctly implementing IDisposable, e.g. MSDN IDisposable, MSDN Implementing IDisposable, An excellent StackOverflow Q&A
However none of them seem to cover a more common use-case I have: what to do when my class has an IDisposable member that lives longer than one method? For example
class FantasticFileService
{
private FileSystemWatcher fileWatch; // FileSystemWatcher is IDisposable
public FantasticFileService(string path)
{
fileWatch = new FileSystemWatcher(path);
fileWatch.Changed += OnFileChanged;
}
private void OnFileChanged(object sender, FileSystemEventArgs e)
{
// blah blah
}
}
The closest MSDN gets to addressing this problem only covers the use-case when the instance of IDisposable is short lived so says call Dispose e.g. by using using:
Implement IDisposable only if you are using unmanaged resources
directly. If your app simply uses an object that implements
IDisposable, don't provide an IDisposable implementation. Instead, you
should call the object's IDisposable.Dispose implementation when you
are finished using it.
of course that is not possible here where we need the instance to survive longer than a method call!?
I suspect the correct way to do this would be to implement IDisposable (passing the responsibility to creator of my class to dispose it) but without all finalizer and protected virtual void Dispose(bool disposing) logic becuase I don't have any unmanged resources, i.e.:
class FantasticFileService : IDisposable
{
private FileSystemWatcher fileWatch; // FileSystemWatcher is IDisposable
public FantasticFileService(string watch)
{
fileWatch = new FileSystemWatcher(watch);
fileWatch.Changed += OnFileChanged;
}
public void Dispose()
{
fileWatch.Dispose();
}
}
But why is this use-case not explicitly covered in any official documentation? And the fact it explicitly says do not implement IDisposable if your class does not have unmanaged resources makes me hesitant to do so... What is a poor programmer to do?

It looks like your case is indeed covered by some documentation, namely the design warning CA1001: Types that own disposable fields should be disposable.
That link has an example of what your IDisposable implementation should look like. It will be something like as follows. Eventual design guidelines can be found at CA1063: Implement IDisposable correctly.
class FantasticFileService : IDisposable
{
private FileSystemWatcher fileWatch; // FileSystemWatcher is IDisposable
public FantasticFileService(string watch)
{
fileWatch = new FileSystemWatcher(watch);
fileWatch.Changed += OnFileChanged;
}
~FantasticFileService()
{
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (disposing && fileWatch != null)
{
fileWatch.Dispose();
fileWatch = null;
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}

As you have gathered, you need to make FantasticFileService:IDisposable disposable too. Dispose() can be used to get rid of managed resources as well as unmanaged.
Try something like this:
class FantasticFileService:IDisposable
{
private FileSystemWatcher fileWatch; // FileSystemWatcher is IDisposable
private bool disposed;
public FantasticFileService(string path)
{
fileWatch = new FileSystemWatcher(path);
fileWatch.Changed += OnFileChanged;
}
private void OnFileChanged(object sender, FileSystemEventArgs e)
{
// blah blah
}
// Public implementation of Dispose pattern callable by consumers.
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
// Protected implementation of Dispose pattern.
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing)
{
if (fileWatch != null)
{
fileWatch.Dispose();
fileWatch = null;
}
// Free any other managed objects here.
//
}
// Free any unmanaged objects here.
//
disposed = true;
}
~FantasticFileService()
{
Dispose(false);
}
}
See also
Implementing a Dispose Method

Instance method call Dispose

Is correct that a public method calls the Dispose of IDisposable in the same class?
E.g.
public class Worker : IDisposable
{
public void Close()
{
SendCloseCommand();
Dispose();
}
public void Dispose()
{
////other resources release
}
private void SendCloseCommand()
{
}
}
Another thing about disposable pattern:
If the Close should be always called, is better that is called from the Dispose method or not?
If not, I should put the usage of the Worker class in a try/catch/finally everywhere, to call the Close. Right?
The correct design should instead be?
public class Worker : IDisposable
{
public void Close()
{
SendCloseCommand();
}
public void Dispose()
{
Close();
////other resources release
}
private void SendCloseCommand()
{
////other stuff
}
}

If you look at Microsoft implementation for StreamReader, Dispose gets called from Close,
public override void Close()
{
Dispose(true);
}
and also the implementation for Dispose closes the stream as well by calling Close of base Stream.
protected override void Dispose(bool disposing)
{
// Dispose of our resources if this StreamReader is closable.
// Note that Console.In should be left open.
try {
// Note that Stream.Close() can potentially throw here. So we need to
// ensure cleaning up internal resources, inside the finally block.
if (!LeaveOpen && disposing && (stream != null))
stream.Close();
}
finally {
if (!LeaveOpen && (stream != null)) {
stream = null;
encoding = null;
decoder = null;
byteBuffer = null;
charBuffer = null;
charPos = 0;
charLen = 0;
base.Dispose(disposing);
}
}
}
In your class implementation, I would call the Dispose from your Close method as you are doing in your first code snippet. In Dispose, I would check for Worker status, if it is not closed then close it using SendCloseCommand, and then release resources.
public void Dispose()
{
if(this.Status != Closed) // check if it is not already closed
{
SendCloseCommand();
}
////other resources release
}
This will ensure your resources disposal, even if your class is used with using statement, or if any one calls Close manually.
Just remember to check status of your Worker object, before issuing Close Command.

Microsoft has some suggestions about having a Close method on a class implementing IDisposable. It is part of the Dispose Pattern guidelines:
CONSIDER providing method Close(), in addition to the Dispose(), if close is standard terminology in the area.
When doing so, it is important that you make the Close implementation identical to Dispose and consider implementing the IDisposable.Dispose method explicitly.
public class Stream : IDisposable {
IDisposable.Dispose(){
Close();
}
public void Close(){
Dispose(true);
GC.SuppressFinalize(this);
}
}
So Microsofts suggestion is to hide Dispose and let it call Close to do the actual cleanup. Also, remember the guideline about multiple calls to Dispose:
DO allow the Dispose(bool) method to be called more than once. The method might choose to do nothing after the first call.
Following these guidelines makes your code consistent with the .NET library and you will avoid any confusion about if your class should be closed or disposed for proper cleanup.