Reuse model binders

[martincostello]

Reuse the same model binders for CancellationTokens and services, rather than allocating a new one for every request with such a parameter.

Both CancellationTokenModelBinder and ServicesModelBinder don't have any state, so it seems that reusing the same instance within the model binder providers (created lazily) would reduce the number of allocations for an application with a controller method similar to the example below:

public async Task<IActionResult> GetForecast(
    string location,
    [FromServices] WeatherClient client,
    CancellationToken cancellationToken)
{
    var forecast = await client.GetForecastAsync(location, cancellationToken);
    return Json(forecast);
}

[pranavkm]

Thanks!

[ghost]

Hello @pranavkm!

Because this pull request has the auto-merge label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

p.s. you can customize the way I help with merging this pull request, such as holding this pull request until a specific person approves. Simply @mention me (@msftbot) and give me an instruction to get started! Learn more here.