Make GetOrCreate(key) atomic on ConcurrentDictionary - #136
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The one-argument GetOrCreate had no ConcurrentDictionary overload, so it bound to the IDictionary one. That does a lookup and then Add, which throws ArgumentException when another caller adds the key in between. Add a ConcurrentDictionary overload that uses GetOrAdd, as the two-argument form already does. Fixes #134 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KaXGMeYeXB1J32kSrLGhgJ
…reate Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KaXGMeYeXB1J32kSrLGhgJ
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This was referenced Sep 28, 2026
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Fixes #134
What was wrong
#131 made
ConcurrentDictionary.GetOrCreate(key, defaultValue)atomic. The one-argumentGetOrCreate(key)had noConcurrentDictionaryoverload, so it bound to theIDictionaryone, which doesTryGetValueand thenAdd. When two callers raced on a missing key, the secondAddthrewArgumentException.Change
Added
GetOrCreate<TKey, TVal>(this ConcurrentDictionary<TKey, TVal>, TKey). It keeps the existing null checks and callsGetOrAdd(key, _ => new TVal()), so every caller gets the stored instance. A newTValis only built when the key is actually missing.Tests
GetOrCreateConcurrentDictionaryWithoutDefaultShouldReturnStoredValueWhenAnotherCallerAddsFirstreuses the existingRacingComparerto add a rival value between the lookup and the add, so the race happens every run. It fails without the library change and passes with it.GetOrCreateConcurrentDictionaryWithoutDefaultShouldReturnSameInstanceToParallelCallersis theParallel.Fortest the issue asked for. It is timing-dependent and passed in the one run without the fix, so the deterministic test above is the real regression guard.dotnet test: 140/140 pass.The triage note also suggested checking the other
IDictionaryextension overloads for the same binding trap. That audit is not part of this PR.🤖 Generated with Claude Code
https://claude.ai/code/session_01KaXGMeYeXB1J32kSrLGhgJ
Generated by Claude Code