fix(ai): resolve race condition in parallel tool execution#11907
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delta575 wants to merge 2 commits intovercel:mainfrom
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fix(ai): resolve race condition in parallel tool execution#11907delta575 wants to merge 2 commits intovercel:mainfrom
delta575 wants to merge 2 commits intovercel:mainfrom
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When multiple tools execute in parallel, the stream could close prematurely or throw "stream is not in a state that permits enqueue" errors. Two issues caused this: 1. generateId() returned the same value for multiple tools in a batch, causing outstandingToolResults Set to only track one tool 2. Multiple finally() blocks calling attemptClose() simultaneously caused race conditions Fix: - Use toolCall.toolCallId instead of generateId() for unique tracking - Add closed flag to prevent re-entry in attemptClose() - Guard async enqueue calls to prevent enqueueing after stream closure Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add tests to verify that: - Using toolCallId for tracking handles parallel tools correctly (exposes bug where generateId returns same value for all tools) - Multiple tools with different delays all complete successfully - Stream doesn't close prematurely when fast tool completes before slow tool - Many parallel tool calls (10+) don't lose results Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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| // close the tool results controller if no more outstanding tool calls | ||
| if (canClose && outstandingToolResults.size === 0) { | ||
| // Mark as closed BEFORE doing any work to prevent race conditions | ||
| // where multiple finally() blocks call attemptClose() simultaneously |
Contributor
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Unguarded stream controller enqueue calls throw errors when stream is closed externally (via AbortSignal), causing uncaught exceptions and silently dropping results
lgrammel
reviewed
Jan 22, 2026
| const toolExecutionId = generateId(); // use our own id to guarantee uniqueness | ||
| // Use toolCallId which is unique per tool call from the LLM | ||
| // (generateId() was returning the same value for multiple tools in a batch) | ||
| const toolExecutionId = toolCall.toolCallId; |
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has this fix been ai generated?
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generateId was used intentionally. if you end up with repeated ids that is most likely an issue with the id generator that you pass in
Collaborator
|
This PR mixes 2 issues. The close state issue seems reasonable, but I have doubts regarding the id generation. Please separate the close fix into a new PR. |
This was referenced Jan 22, 2026
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Background
When multiple tools execute in parallel during
streamText, the stream could close prematurely or throw "The stream is not in a state that permits enqueue" errors.Context: We're using
@convex-dev/agent0.3.2 which doesn't support AI SDK v6. We wanted to use Gemini 3 Flash, butthought_signatureis required (not optional), so we had to downgrade to Gemini 2.5 where it's optional and AI SDK v5 worked fine. When testing AI SDK v6 compatibility via get-convex/agent#208 in preparation for Gemini 3 support, we encountered this race condition - Gemini 3 Flash aggressively uses parallel tool calls which exposed the bug.Summary
Two issues caused this race condition:
Non-unique tool tracking IDs:
generateId()was returning the same value for multiple tools in a batch, causing theoutstandingToolResultsSet to only track one tool. When that tool completed, the stream closed while others were still running.Re-entry in attemptClose: Multiple
finally()blocks could callattemptClose()simultaneously, causing race conditions when closing the stream.Fix:
toolCall.toolCallIdinstead ofgenerateId()for unique tool trackingclosedflag to prevent re-entry inattemptClose()Manual Verification
Tested with a Convex application using
@convex-dev/agentfrom get-convex/agent#208 and Gemini 3 Flash with 5+ parallel tool calls - all tool results are now captured and streaming completes successfully.Checklist