Replace a couple of Hashtables in CoreLib with ConcurrentDictionary #122918
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Avoids boxing keys/values, makes things more strongly typed, and reduces some ceremony.
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Pull request overview
This PR modernizes two classes in CoreLib by replacing legacy Hashtable collections with strongly-typed ConcurrentDictionary<TKey, TValue>, eliminating boxing/unboxing overhead and reducing code ceremony.
Key Changes
- Replaced
Hashtable.Synchronized()withConcurrentDictionaryfor type safety and better performance - Simplified cache lookup patterns by using
GetOrAdd()method instead of manual check-add-lock logic - Adopted modern C# syntax (collection expressions and expression-bodied members)
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/libraries/System.Private.CoreLib/src/System/Text/EncodingTable.cs | Replaced Hashtable with ConcurrentDictionary<string, int> for encoding name-to-codepage mapping; simplified lookup logic using GetOrAdd |
| src/libraries/System.Private.CoreLib/src/System/CurrentSystemTimeZone.cs | Replaced Hashtable with ConcurrentDictionary<int, DaylightTime> for year-to-daylight-changes caching; eliminated manual double-check locking pattern |
src/libraries/System.Private.CoreLib/src/System/Text/EncodingTable.cs
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src/libraries/System.Private.CoreLib/src/System/CurrentSystemTimeZone.cs
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tarekgh
approved these changes
Jan 6, 2026
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tarekgh
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Modulo copilot comments, LGTM!
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
This was referenced Jan 9, 2026
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Avoids boxing keys/values, makes things more strongly typed, and reduces some ceremony.