PredictionEnginePool.GetPredictionEngine is not thread safe

[thomasrosdahl]

System information

• OS version/distro: Windows 10
• .NET Version (eg., dotnet --info): Azure Functions Runtime 2.7.1948

Issue

• What did you do?
  Invoked PredictionEnginePool.Predict("MyModelName", example) from multiple threads.

• What happened?
  System.ArgumentException: 'An item with the same key has already been added. Key: MyModelName'

• What did you expect?
  Method is thread safe so that multiple named pools cannot be created simultaneously.

Source code / logs

at System.ThrowHelper.ThrowAddingDuplicateWithKeyArgumentException[T](T key)
at System.Collections.Generic.Dictionary2.TryInsert(TKey key, TValue value, InsertionBehavior behavior) at Microsoft.Extensions.ML.PredictionEnginePool2.GetPredictionEngine(String modelName)
at Microsoft.Extensions.ML.PredictionEnginePoolExtensions.Predict[TData,TPrediction](PredictionEnginePool`2 predictionEnginePool, String modelName, TData example)

[gvashishtha]

@frank-dong-ms

[frank-dong-ms-zz]

Fix has been checked in.