Fix TokenBucketRateLimiter AttemptAcquire(0) with fractional tokens#124498
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apoorvdarshan wants to merge 1 commit intodotnet:mainfrom
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Fix TokenBucketRateLimiter AttemptAcquire(0) with fractional tokens#124498apoorvdarshan wants to merge 1 commit intodotnet:mainfrom
apoorvdarshan wants to merge 1 commit intodotnet:mainfrom
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…al _tokenCount Change availability checks from > 0 / != 0 to >= 1 so fractional tokens below 1.0 are not treated as available permits, making AttemptAcquire(0) consistent with GetStatistics().CurrentAvailablePermits. Fixes dotnet#118192
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Pull request overview
This PR fixes a bug in TokenBucketRateLimiter where AttemptAcquire(0) incorrectly succeeded when fractional tokens were present (e.g., _tokenCount = 0.5). The issue arose because _tokenCount is stored as a double for accurate replenishment calculations, but availability checks used > 0 or != 0 instead of >= 1, causing inconsistency with GetStatistics().CurrentAvailablePermits which truncates to long.
Changes:
- Changed three availability checks from
> 0/!= 0to>= 1to ensure fractional tokens are not treated as available permits - Added regression test
AttemptAcquireZeroWithFractionalTokensReportsUnavailablethat verifies the probe behavior with fractional tokens
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/libraries/System.Threading.RateLimiting/src/System/Threading/RateLimiting/TokenBucketRateLimiter.cs | Fixed three conditions in AttemptAcquireCore, AcquireAsyncCore, and TryLeaseUnsynchronized to check _tokenCount >= 1 instead of > 0 or != 0 |
| src/libraries/System.Threading.RateLimiting/tests/TokenBucketRateLimiterTests.cs | Added regression test that drains tokens, replenishes to create fractional tokens (~0.5), and verifies AttemptAcquire(0) correctly returns unavailable |
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Summary
AttemptAcquire(0)incorrectly succeeding when_tokenCountholds a fractional value (e.g.0.5) by changing three availability checks from> 0/!= 0to>= 1AttemptAcquire(0)consistent withGetStatistics().CurrentAvailablePermits, which truncates to(long)and reports0Fixes #118192
Test plan
AttemptAcquireZeroWithFractionalTokensReportsUnavailablepassesTokenBucketRateLimiterTestscontinue to passdotnet test src/libraries/System.Threading.RateLimiting/tests/System.Threading.RateLimiting.Tests.csproj🤖 Generated with Claude Code