🤖 fix: serialize concurrent bash_output calls to prevent duplicate output #1093
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…tput Fixes race condition where parallel bash_output tool calls on the same process could both read from the same offset before either updates the read position, resulting in duplicate output being returned. Root cause: When disableParallelToolUse is false (our default), Claude can issue multiple bash_output calls in a single response. Without serialization, both calls would: 1. Read proc.outputBytesRead = 0 2. Start async readOutput(0) 3. Both read same content 4. Both set proc.outputBytesRead to same final value Fix: Add outputLock (AsyncMutex) to BackgroundProcess to serialize getOutput() calls. Also consolidate all per-process state (outputBytesRead, outputLock) into the BackgroundProcess object so cleanup is automatic when the process is removed from the processes map - no separate maps to keep in sync. _Generated with mux_
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ammario
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Dec 11, 2025
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Fixes race condition where parallel
bash_outputtool calls on the same process could both read from the same offset before either updates the read position, resulting in duplicate output being returned.Root Cause
When
disableParallelToolUseis false (our default), Claude can issue multiplebash_outputcalls in a single response. Without serialization, both calls would:pos.outputBytes = 0readOutput(0)pos.outputBytesto same final valueFix
AsyncMutex(using existing codebase pattern fromStreamManager) to serializegetOutput()callsreadPositionsandoutputLocksmaps duringcleanup()to prevent stale stateTest
Added test case that calls
getOutput()twice in parallel and verifies combined output contains each line exactly once (no duplicates).Generated with
mux