[release/10.0] Fix hash collision in TypeMapLazyDictionary causing non-deterministic ArgumentException #123517
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…nstead of hash codes Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>
Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>
Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>
Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>
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Backport of #123502 to release/10.0
/cc @AaronRobinsonMSFT @copilot
Customer Impact
When large numbers of
TypeMapAssociationAttributeexist, it can occur that collisions of type names (strings) occur. The current approach ignored the possibility of collision and simply acquired the result ofGetHashCode()and inserted that as a key into aDictionary<,>. This meant there was no opportunity to handle the case when two non-equalstringinstances generate the same hash code. Using the hash code directly was done to avoid the non-trivial increase in memory usage imposed by using thestringinstances as the key.The solution is to use the
stringas the key instead.Regression
Testing
Verified using a CsWinRT repro case. Prior to this fix a collision would occur 1 / 100 times run. After this change the repro ran for more than 1000 iterations with no collisions.
Risk
Low. This new approach does increase the baseline amount of memory when the
TypeMapis used on coreclr. This was deemed acceptable since the coreclr isn't considered the P1 scenario forTypeMap. The native AOT, the P1 scenario forTypeMap, is not impacted by this change.