Improve performance with many threads

[304NotModified]

See NLog/NLog#2064

[codecov]

Codecov Report

Merging #133 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #133   +/-   ##
=======================================
  Coverage   59.03%   59.03%           
=======================================
  Files          25       25           
  Lines         310      310           
  Branches       77       77           
=======================================
  Hits          183      183           
  Misses         91       91           
  Partials       36       36

Impacted Files	Coverage Δ
...etCore/LayoutRenderers/AspNetLayoutRendererBase.cs	87.5% <ø> (ø)	⬆️

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[snakefoot]

@304NotModified If the usage of ServiceLocator.ServiceProvider should be avoided. Then maybe these should also be fixed:

• AspNetEnvironmentLayoutRenderer.cs
• IISInstanceNameLayoutRenderer.cs

[304NotModified]

thanks will check them!

[snakefoot]

@304NotModified Wondering if it would make sense also to add:

protected override void CloseLayoutRenderer()
{
   _httpContextAccessor = null;
   base.CloseLayoutRenderer();
}

[304NotModified]

good idea! Added to #134