External Evaluation leads to Exceptions during Object Graph Traversal

[abeham]

Instances from System.Net.Sockets are part of the object graph. The following exception is thrown when an algorithm is stopped

System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Net.Sockets.IPPacketInformation.GetHashCode()
   at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
   at System.Collections.Generic.HashSet`1.InternalGetHashCode(T item)
   at System.Collections.Generic.HashSet`1.Contains(T item)
   at HeuristicLab.Common.ObjectExtensions.<GetChildObjects>d__3.MoveNext() in C:\...\HeuristicLab.Common\3.3\ObjectExtensions.cs:line 136
   at HeuristicLab.Common.ObjectExtensions.GetObjectGraphObjects(Object obj, HashSet`1 excludedMembers, Boolean excludeStaticMembers) in C:\...\HeuristicLab.Common\3.3\ObjectExtensions.cs:line 56
   at HeuristicLab.Optimization.Algorithm.OnStopped() in C:\...\HeuristicLab.Optimization\3.3\Algorithms\Algorithm.cs:line 303
   at HeuristicLab.Core.Executable.OnStopped() in C:\...\HeuristicLab.Core\3.3\Executable.cs:line 138
   at HeuristicLab.Core.Engine.Start(CancellationToken cancellationToken) in C:\...\HeuristicLab.Core\3.3\Engine.cs:line 100
   at HeuristicLab.Optimization.EngineAlgorithm.Start(CancellationToken cancellationToken) in C:\...\HeuristicLab.Optimization\3.3\Algorithms\EngineAlgorithm.cs:line 172
   at System.Threading.Tasks.Task.Execute()

The error exists at least since 3.3.13, however, no exception window has been shown in earlier versions when object graph traversal failed. Probably some changes in 3.3.15 regarding Sync/Async has led to these exceptions being properly raised.

[abeham]

Patch by ddorfmei

[abeham]

r16648: exclude types from System.Net.Sockets in object graph traversal

Another option would be to just disregard the socket field in the EvaluationTCPChannel class (HeuristicLab.Problems.ExternalEvaluation-3.4) with the ExcludeFromObjectGraphTraversal attribute (see #2626, r14032). However, I think we can safely ignore everything from System.Net.Sockets.

[gkronber]

Reviewed r16648. Thanks.

[abeham]

r16650: merged to stable