Implementing Custom Awaiters

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Implementing Custom Awaiters

In C#, any type can be awaited if it follows the 'GetAwaiter' pattern. This expert-level technique allows you to create custom asynchronous primitives without relying on Task or ValueTask, reducing allocation overhead in specialized high-performance scenarios.

snippet.csharp
csharp
public struct MyTaskAwaiter : INotifyCompletion {
    public bool IsCompleted => false;
    public void OnCompleted(Action continuation) => Task.Run(continuation);
    public void GetResult() { }
}
 
public struct MyCustomTask {
    public MyTaskAwaiter GetAwaiter() => new MyTaskAwaiter();
}

Breakdown

public bool IsCompleted => false;

Determines if the operation is already finished; if false, the state machine yields.

public MyTaskAwaiter GetAwaiter()

The duck-typing method the compiler looks for to enable the 'await' keyword.

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Implementing Custom Awaiters

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