Do you use the asynchronous Dispose method, know the advantages and precautions and how to use it?

Let’s level up, or rather, quickly review this topic before discussing the asynchronous dispose method.

Why do the Dispose and Finalize methods exist?

.NET is a managed environment, in other words, it is responsible for allocating and releasing memory and managing the lifetime of the objects it creates.

But what about when these objects are under the domain and control of the operating system (the famous unmanaged objects like files, ports, network, and others)?

That’s where the Dispose and Finalize methods come in, making a “bridge” between these two environments, enabling the management of these resources.

The Dispose method is used to explicitly (via code) release the resources (unmanaged) before the environment releases the object. The Finalize method, on the other hand, is implicitly and non-deterministically called by the managed environment to release this resource allocated in memory during or at the end of the application’s execution.

Both methods aim to inform the operating system which unmanaged resource allocated in memory needs to be released.

In summary, you control when and where to use the Dispose method, while you do not control the Finalize method; only the environment can call it directly, and it has a much higher “cost” for your application in terms of performance and memory management depending on the scenario.

The best ways to use them and details of the differences between them and other characteristics and behaviors are not the focus of the topic we are presenting.

I will be happy to detail this in another article if there are many requests in the comments.

Why was the asynchronous Dispose method created?

As explained earlier, Dispose is used to explicitly (via code) release the resources (unmanaged).

For this release execution, which is done synchronously, it is necessary to interrupt the current execution thread so that the managed environment “talks” to the operating system and waits for the release tasks to execute and return for the application to continue its task.

This synchronous execution journey is not advantageous for more modern applications and languages that make use of multiple available processor cores.

With this in mind, the possibility of using the IAsyncDisposable interface was introduced as part of C# 8.0 (September 2019!) to enable the asynchronous disposal of unmanaged resources.

In addition to this improvement, over time, several other improvements have been made in .NET CORE to allow asynchronous operations, adapting the ecosystem as a whole to efficiently take advantage of the resources of multiple processor cores, which we call multi-threading and “parallel” processing.

Main advantages of asynchronous Dispose

Higher Performance: Asynchronous operations allow the system to continue executing other tasks while waiting for the dispose to complete, resulting in more efficient use of resources.

Better Scalability: Applications that use asynchronous dispose can handle more simultaneous requests, becoming more scalable.

Reduction of Blocking: Since operations do not need to wait for each other, there are fewer blocks and bottlenecks in the system.

An example of benefit in a typical scenario

All services you registered as Scoped (i.e., they only exist during the current HTTP request) that implement IAsyncDisposable will be disposed of asynchronously at the end of the request, freeing up time and resources to process other actual requests.

Does IAsyncDisposable replace IDisposable?

Straight to the point: NOOOOO! The IAsyncDisposable interface is not a replacement for IDisposable. It is an additional form of disposal mainly for creating libraries (which do not control the code that uses the object that needs to be disposed of).

If you implement only IAsyncDisposable, your application may have resource leaks or even an exception depending on the scenario.

A relevant point for using it as an additional form is that there are some implementations that make use of abstractions or reflection in search of the IDisposable interface, and as they will not find it, we will certainly have problems during execution.

Another relevant point is the implementation within synchronous methods requiring the blocking of the context to synchronize it, which makes the asynchronous use lose its meaning (see the image below).

How to implement IAsyncDisposable along with IDisposable

There is a difference in the asynchronous disposal pattern compared to the synchronous one. This difference helps ensure functional equivalence with the synchronous disposal pattern.

In other words, the DisposeAsyncCore() method will dispose of managed resources asynchronously, so it is not recommended to dispose of them synchronously. Therefore, call Dispose(false) instead of Dispose(true) to ensure this behavior.

Tip: If an implementation is sealed, the DisposeAsyncCore() method will not be necessary, and asynchronous cleanup can be performed directly in the IAsyncDisposable.DisposeAsync() method.

Be careful with stacking

If an exception is thrown (example below) in the AnotherAsyncDisposable constructor, no object will be disposed of correctly.

The example of a better stacking construction is shown below, ensuring the correct disposal for each object creation.

Some disadvantages of applying asynchronous Dispose

Complexity: Implementing and managing asynchronous operations can add complexity to the code. This includes the need to handle exceptions and ensure that all resources are correctly released.

Resource Overhead: Although asynchronous operations can improve scalability, they can also introduce resource overhead, such as increased memory and thread usage.

Debugging Difficulty: Debugging asynchronous code can be more complicated than debugging synchronous code. Exceptions can be harder to track and understand, especially when they occur in different execution contexts.

Testing Complexity: Testing asynchronous code can be more complex, requiring specific tools and approaches to ensure that all conditions and exceptions are correctly handled.

Conclusion

Much is said about the use of asynchronous Dispose, and it can be advantageous mainly for scenarios where resource usage is expensive, such as in cloud environments, and performance, scalability, and few blocks are highly desired factors.

However, be careful when using them and add them only if you really need to balance the disadvantages.