[perf] DefaultActionSelector.HasValidAction allocate significant memory, which can be fixed.

[troydai]

Following data shows up in MusicStore (CLR) perf profiling:

Name
 Type Enumerator[Microsoft.AspNet.Mvc.RouteDataActionConstraint]
+ CLR <<clr!JIT_New>>
 + LIB <<System.Core.ni!System.Linq.Enumerable.All[System.__Canon](System.Collections.Generic.IEnumerable`1, System.Func`2)>>
  + module Microsoft.AspNet.Mvc.Core <<Microsoft.AspNet.Mvc.Core!Microsoft.AspNet.Mvc.DefaultActionSelector+<>c__DisplayClass20.<HasValidAction>b__21(class Microsoft.AspNet.Mvc.ActionDescriptor)>>
   + LIB <<System.Core.ni!System.Linq.Enumerable.Any[System.__Canon](System.Collections.Generic.IEnumerable`1)>>
    + module Microsoft.AspNet.Mvc.Core <<Microsoft.AspNet.Mvc.Core!MvcRouteHandler.GetVirtualPath>>
     + module Microsoft.AspNet.Routing <<Microsoft.AspNet.Routing!RouteCollection.GetVirtualPath>>

[danroth27]

@troydai Can you please more details in the bug on how much memory is actually getting allocated and what scenarios are affected? Thanks!

[troydai]

In a bottom up investigation of Music Store desktop memory consumption, following call took 2.1% of the total memory usage inclusively:

Name                                                                                                                                                                                                Exc %   Exc Exc Ct  Inc %
module Microsoft.AspNet.Mvc.Core <<Microsoft.AspNet.Mvc.Core!Microsoft.AspNet.Mvc.DefaultActionSelector+<>c__DisplayClass20.<HasValidAction>b__21(class Microsoft.AspNet.Mvc.ActionDescriptor)>>      0.0     0      0    2.2

The memory were all spent on

LIB <<System.Core.ni!System.Linq.Enumerable.All[System.__Canon](System.Collections.Generic.IEnumerable`1, System.Func`2)>>

Here's the source codes:

        public virtual bool HasValidAction([NotNull] VirtualPathContext context)
        {
            if (context.ProvidedValues == null)
            {
                // We need the route's values to be able to double check our work.
                return false;
            }

            var actions =
                GetActions().Where(
                    action =>
                        action.RouteConstraints == null ||
                        action.RouteConstraints.All(constraint => constraint.Accept(context.ProvidedValues)));

            return actions.Any();
        }

Should these route constraints be cached, the memory consumption can be reduce to minimal.

[rynowak]

we actually already have the cache this would be a straightforward code change to remove some linq from a hot path

[yishaigalatzer]

144a4b5