Avoid duplicate GetHashCode() values in TokenMap#48897
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cston merged 1 commit intodotnet:masterfrom Oct 25, 2020
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Could you share some details about this being the root of the issue? I'm missing the link. Thanks |
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@jcouv, I've updated the description with details, thanks. |
jaredpar
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That does seem a bit suspicious and contrary to my intuition here. |
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TokenMapstores symbols used in code generation in a dictionary mapped to index. The symbols are compared by reference* so, ideally, the hash codes for the symbols should be distinct if the symbols are distinct instances.Fixes #48886.
In the bug repro, many symbols are added to the map for the same method (a
SubstitutedMethodSymbolfor an anonymous type constructor). The map was usingSubstitutedMethodSymbol.GetHashCode()for those symbols so the dictionary performed poorly (inConcurrentDictionary<IReferenceOrSignature, uint>.TryAdd(TKey, TValue)in particular) since many items had the same hash code value.*There is a separate question of whether
TokenMapshould contain separate entries for multiple instances of the same symbol. I will confirm.[Thanks to @jaredpar for suggesting hashcode collisions as the issue.]