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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.

IAsyncDisposable reference implementation error?

Microsoft provides a refence implementation for classes that need to implement both IDisposable and IAsyncDisposable, say because they have members of both of these.
https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/implementing-disposeasync
I include the full implementation below. These lines in Dispose(disposing) are the part I don't understand.
(_asyncDisposableResource as IDisposable)?.Dispose();
...
_asyncDisposableResource = null;
It seems like if I have an instance of CustomDisposable and Dispose() gets called on it before DisposeAsync() then the _asyncDispoableResource field will have Dispose() called on it instead of DisposeAsync (if it has one), and then get set to null unconditionally. Seems like _asyncDispoableResource never gets disposed of properly in this case, even if DisposeAsync() gets called on the CustomDisposable instance later.
Full reference code:
using System;
using System.IO;
using System.Threading.Tasks;
namespace Samples
{
public class CustomDisposable : 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();
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().ConfigureAwait(false);
}
if (_disposableResource is IAsyncDisposable disposable)
{
await disposable.DisposeAsync().ConfigureAwait(false);
}
else
{
_disposableResource.Dispose();
}
_asyncDisposableResource = null;
_disposableResource = null;
}
}
}

Quoting your reference:
It is typical when implementing the IAsyncDisposable interface that classes will also implement the IDisposable interface. A good implementation pattern of the IAsyncDisposable interface is to be prepared for either synchronous or asynchronous dispose.
This means that it should be sufficient to dispose an object via "classic" Dispose, it should not matter that DisposeAsync is never called. This is why the resource is set to null, so it is clear that it has already been disposed asynchonously. The actual implementation of the disposable reference has to be prepared for this.

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.

Reason for Using IDisposable Interface

We all know that IDisposable interface is using for disposing unmanaged resources.
I have a class which contains following code. here i have implemented the Dispose method from IDisposable interface.
class ClassA:IDisposable
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
What my doubt is why i need to implement the Dispose method from IDisposable interface?. Instead of that i can create my own Dispose method in my class without inheriting from IDisposable interface which i have given below.
for the class below i haven't inherited my class from IDisposable interface. instead of that i created my own dispose method. this also works fine.
class ClassA
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
So can any one tel me tat the reason behind of implementing dispose method from IDisposable interface.

When you implement IDisposable, you can use using for exception-safe disposing.

Two reasons:
Implementing IDisposable expresses intent (this should be disposed) in a conventional manner. It's easy to spot that you should dispose of a resource if it implements IDisposable, whereas relying on other developers to read the documentation carefully is more likely to lead to errors.
That convention is used by the using statement. You should be able to write:
using (ClassA foo = new ClassA())
{
...
}
... but unless you implement IDisposable, you can't.
(Personally I wouldn't include a finalizer, by the way... that's usually only for directly held unmanaged resources; here you should rely on the Image finalizer.)

Although implementing your own dispose method will suffice for any explicit call made to that method but when,after implementig Idispobale, you use a using statement, the built in .Net functionality will invoke your dispose method for you so your code can look like this;
using (ClassA foo = new ClassA())
{
...
}
rather than this
using (ClassA foo = new ClassA())
{
....
foo.Dispose();
}

When you implement IDisposable interface you can use your class in using block, like this:
...
using(var classA = new ClassA())
{
do some stuff
}
after it your Dispose method will be invoked.
It is quite useful.

IDisosable is very useful. For example working with Database connections. It requires all of its implementations to have Dispose method.
It is very useful for working with unmanaged resources, where you have to release them as for the Database connections above, because Garbage Collector is working on managed code (it releases objects where they are not in use anymore), but for unmanaged as C++ application or library (without CLR), it has no idea what is going there. By using its disposable method you say you have finished your work with such a resource and it is being released (freeing memory).
Example (example class and usage):
class Database : IDisposable
{
private SqlConnection _conn;
public Database(string conn_str)
{
// Doing the connectivity
}
public Dataset Read(string sql)
{
SqlCommand cmd = new SqlCommand();
Dataset result = null;
// etc...
return result;
}
public Dispose()
{
_conn.Close();
}
}
using(Database db = new Database(conn_string))
{
Dataset ds = db.Read("SELECT something FROM table");
}
The this approach is very useful. In this statement you init your IDisposable and at the end of statement (not needed to call db.Dispose()) its Dispose() is called and the resources are freed. In this case unmanaged resource may be the .NET SQL Driver, you can use MySQL library, etc.

Three "unwritten" parts of the contract for .net objects are:
If a class implements IDisposable, then once the instance is no longer needed, calling IDisposable.Dispose() on it and abandoning it should take care of all necessary cleanup, regardless of the type of object.
If an object does not implement IDisposable, it may be safely abandoned any time it is no longer needed, without requiring any cleanup.
An object which constructs an instance of a class which implements IDisposable is responsible for ensuring that IDisposable gets called, either by doing it itself when it is done with the object, or ensuring that the reference gets handed off to some other object which will carry out the responsibility.
This is in general a very useful pattern. While there are some rare occasions when it will be impossible for a class to properly implement IDisposable (most commonly because the class exists to expose a complex resource whose cleanup semantics are understood by the user of the class, but not by the class itself), it's very useful to have a unified means of cleanup when things like exceptions occur.

Proper way to dispose of Quartz.NET?

I am using Quartz.NET in an application. What is the proper way to dispose of Quartz.NET.
Right now I am just doing
if (_quartzScheduler != null)
{
_quartzScheduler = null;
}
Is that enough or should I implement a dispose or something in the jobType class?
Seth

scheduler.Shutdown(waitForJobsToComplete: true);
Of course, if you're not on C# 4.0 yet, named parameters don't work:
scheduler.Shutdown(true);

This is not a complete example but might get you on the right path. I would implement something like this:
class customSchedulerClass : IDisposable
{
private Component component = new Component();
private bool disposed = false;
public void scheduleSomeStuff()
{
//This is where you would implement the Quartz.net stuff
}
public void Dispose()
{
Dispose(true);
GC.SupressFinalize(this);
}
private void Dispose(bool disposing)
{
if(!this=disposed)
{
if(disposing)
{
component.dispose;
}
}
disposed = true;
}
}
Then with this you can do cool stuff like using statements:
public static void Main()
{
using (customSchedulerClass myScheduler = new customSchedulerClass())
{
c.scheduleSomeStuff();
}
console.WriteLine("Now that you're out of the using statement the resources have been disposed");
}
So basically by implementing you code while inheriting the functionality of IDisposable you can then us the using statement and when you're done it will cleanly dispose your resources and keep things nice and clean. (Disclaimer, again this is not a complete example, just to get you in the right direction).

The docs don't say anything about IScheduler implementing IDisposable. If you have custom job types that grab and hold resources (file locks, database connections), you can implement IDispoable and override Dispose() on your object to release resources.

Generally we don't need to set an object to null in order to dispose it off.
If an object contains unmanaged resources then it should implement IDisposable (and be called by all its clients).
You can refere this similar post.