fix: add mutex to Cloudability emitter for concurrent Emit() safety#154
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fix: add mutex to Cloudability emitter for concurrent Emit() safety#154
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Adds sync.Mutex to the Cloudability Emitter struct to protect mutable state (sampleCt, currentSamplePath, nextSamplePath, lastEmission) from concurrent access when Emit() is called from overlapping goroutines in the export loop. Also protects ClearOldScratchSamples() which calls Uploader.RemoveSample() and races with AddSample() in Emit(). Follow-up to #151. Minimal change: one import, one struct field, three lines in two methods. Init() and ID() are not locked — Init() runs sequentially before the loop, ID() returns a constant. Includes concurrency test that validates under -race.
Split ClearOldScratchSamples into public (locked) and private (unlocked) methods to prevent deadlock when called from within Emit()'s lock scope. The call chain Emit() -> writeStatsData() -> writeStatsFile() -> ClearOldScratchSamples() would previously deadlock because sync.Mutex is not reentrant in Go. Now writeStatsFile() calls clearOldScratchSamplesLocked() which assumes the caller already holds the lock, while external callers use the public ClearOldScratchSamples() which acquires the lock.
daniel-spray
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Feb 24, 2026
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daniel-spray
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daniel-spray
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LGTM, thank you! Let's run it on uw2p-akp-j1 for 24-48hrs just to ensure we don't find anything unexpected :)
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Adds sync.Mutex to the Cloudability Emitter struct to protect mutable state (sampleCt, currentSamplePath, nextSamplePath, lastEmission) from concurrent access when Emit() is called from overlapping goroutines in the export loop.
Also protects ClearOldScratchSamples() which calls Uploader.RemoveSample() and races with AddSample() in Emit().
Follow-up to #151. Minimal change: one import, one struct field, three lines in two methods.
Init() and ID() are not locked — Init() runs sequentially before the loop, ID() returns a constant.
Includes concurrency test that validates under -race.