EF7 Interleaving guard and ViewComponents

[balneaves]

I updated to the latest rc2/unstable packages (mvc 6.0.0-rc2-16683, ef 7.0.0-rc2-16583), and previously working code now throws the following error :
NotSupportedException: A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe. Microsoft.Data.Entity.Internal.ConcurrencyDetector.EnterCriticalSection()

Not sure if this is an issue with my code, with EF or with MVC, but it comes when using async ViewComponents:

1. Page that loads multiple of the same ViewComponent @await Component.InvokeAsync("SomeViewComponent", Model, stage)
2. Both View/Controller and ViewComponent utilize the same Service (although injected through constructors rather than passed as params)
3. EF7 is injected using the standard services.AddEntityFramework()
4. ViewComponent calls a service to do the EF query (service injected as AddScoped)
5. None of my code/queries call any Async methods (other than the Mvc sucks bro #1 above)
6. Error is thrown on calling `.ToList()' on the query.
7. Only occurs if the query returns results
8. Only occurs if more than 1 ViewComponent is called (that uses the same data)... if I hardcode the foreach in my View to only render the first element it all works
9. No writing done, only reads

Related to : dotnet/efcore#3291

Full stack:

System.NotSupportedException: A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.
   at Microsoft.Data.Entity.Internal.ConcurrencyDetector.EnterCriticalSection()
   at Microsoft.Data.Entity.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
   at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.Contains[TSource](IEnumerable`1 source, TSource value, IEqualityComparer`1 comparer)
   at lambda_method(Closure , TransparentIdentifier`2 )
   at System.Linq.Enumerable.<>c__DisplayClass6_0`1.<CombinePredicates>b__0(TSource x)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at Microsoft.Data.Entity.Query.Internal.LinqOperatorProvider.<_TrackEntities>d__15`2.MoveNext()
   at Microsoft.Data.Entity.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at MyProject.Services.PipelineService.GetValidVersionsForStage(PipelineStage stage, Component component, Int32 max)
   at MyProject.ViewComponents.PipelineApprovalActionViewComponent.Invoke(Component component, PipelineStage pipelineStage)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.AspNet.Mvc.ViewComponents.DefaultViewComponentInvoker.InvokeSyncCore(MethodInfo method, ViewComponentContext context)
   at Microsoft.AspNet.Mvc.ViewComponents.DefaultViewComponentInvoker.<InvokeAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.Mvc.ViewComponents.DefaultViewComponentHelper.<InvokeAsync>d__11.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CallSite.Target(Closure , CallSite , Object )
   at Asp.ASPV__Views_Component_Index_cshtml.<ExecuteAsync>d__22.MoveNext()```

[balneaves]

I solved this by forcing my services to return/use lists rather than queries when using async viewcomponents