Metalama.Community.AutoCancellationToken 2024.1.25

Metalama.Community.AutoCancellationToken

Automatically propagates CancellationToken parameter to async methods and method calls within them.

This is a Metalama aspect. It modifies your code during compilation by using source weaving.

Example

Your code:

[AutoCancellationToken]
class C
{
    async Task MakeRequests(CancellationToken ct)
    {
        using var client = new HttpClient();
        await MakeRequest(client);
    }

    private static async Task MakeRequest(HttpClient client) => await client.GetAsync("https://example.org");
}

What gets compiled:

class C
{
    async Task MakeRequests(CancellationToken ct)
    {
        using var client = new HttpClient();
        await MakeRequest(client, ct);
    }

    private static async Task MakeRequest(HttpClient client, CancellationToken cancellationToken = default) => await client.GetAsync("https://example.org", cancellationToken);
}

Notice that CancellationToken parameter was added to the declaration of MakeRequest and that CancellationToken argument was added to the calls of MakeRequest and HttpClient.GetAsync.

Installation

Install the NuGet package: dotnet add package Metalama.Community.AutoCancellationToken.

How to use

Add [AutoCancellationToken] to the types where you want it to apply.

By annotating a type with [AutoCancellationToken], you add cancellation to all its async methods. Specifically:

• A CancellationToken parameter is added to all async methods that don't have it.
• A CancelltionToken argument is added to calls within async methods where:
  • CancellationToken can be added as a last argument and the added argument corresponds to a CancellationToken parameter (e.g. it's not a params object[] parameter or a generic parameter). The added argument can result in calling a different overload of the method, or specifying a value for an optional parameter.
  • The call is not in a static local function.
  • The containing method doesn't have two or more CancellationToken parameters, since it wouldn't be clear which one to use.