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[PR #6739] fix: prevent async functional API from double-consuming interrupt resume values #5257

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opened 2026-02-20 17:51:27 -05:00 by yindo · 0 comments
yindo commented 2026-02-20 17:51:27 -05:00
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Original Pull Request: https://github.com/langchain-ai/langgraph/pull/6739

State: open
Merged: No

Fix for issue #6660.

In async mode, both parent and child scratchpads were capturing references to the same resume tuple in pending_writes. When both attempted to consume the value, it caused iterations to be skipped (e.g., output 1, 123, 12345 instead of expected 1, 12, 123, 1234, 12345).

The fix ensures child scratchpads always delegate to parent for null_resume, preventing the double-consumption race condition. Only the parent scratchpad now 'owns' the resume value lookup.

Thank you for contributing to LangGraph! Follow these steps to mark your pull request as ready for review. If any of these steps are not completed, your PR will not be considered for review.

  • PR title: Follows the format: {TYPE}({SCOPE}): {DESCRIPTION}

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    • Once you've written the title, please delete this checklist item; do not include it in the PR.

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  • Add tests and docs: If you're adding a new integration, you must include:

    1. A test for the integration, preferably unit tests that do not rely on network access,
    2. An example notebook showing its use. It lives in docs/docs/integrations directory.

  • Lint and test: Run make format, make lint and make test from the root of the package(s) you've modified. We will not consider a PR unless these three are passing in CI. See contribution guidelines for more.

Additional guidelines:

  • Make sure optional dependencies are imported within a function.
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**Original Pull Request:** https://github.com/langchain-ai/langgraph/pull/6739 **State:** open **Merged:** No --- Fix for issue #6660. In async mode, both parent and child scratchpads were capturing references to the same resume tuple in pending_writes. When both attempted to consume the value, it caused iterations to be skipped (e.g., output 1, 123, 12345 instead of expected 1, 12, 123, 1234, 12345). The fix ensures child scratchpads always delegate to parent for null_resume, preventing the double-consumption race condition. Only the parent scratchpad now 'owns' the resume value lookup. Thank you for contributing to LangGraph! Follow these steps to mark your pull request as ready for review. **If any of these steps are not completed, your PR will not be considered for review.** - [ ] **PR title**: Follows the format: {TYPE}({SCOPE}): {DESCRIPTION} - Examples: - feat(core): add multi-tenant support - fix(cli): resolve flag parsing error - docs(openai): update API usage examples - Allowed `{TYPE}` values: - feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert, release - Allowed `{SCOPE}` values (optional): - langgraph, docs, cli, checkpoint, checkpoint-postgres, checkpoint-sqlite, prebuilt, scheduler-kafka, sdk-py - Once you've written the title, please delete this checklist item; do not include it in the PR. - [ ] **PR message**: ***Delete this entire checklist*** and replace with - **Description:** a description of the change. Include a [closing keyword](https://docs.github.com/en/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword) if applicable. - **Issue:** the issue # it fixes, if applicable - **Dependencies:** any dependencies required for this change - **Twitter handle:** if your PR gets announced, and you'd like a mention, we'll gladly shout you out! - [ ] **Add tests and docs**: If you're adding a new integration, you must include: 1. A test for the integration, preferably unit tests that do not rely on network access, 2. An example notebook showing its use. It lives in `docs/docs/integrations` directory. - [ ] **Lint and test**: Run `make format`, `make lint` and `make test` from the root of the package(s) you've modified. We will not consider a PR unless these three are passing in CI. See [contribution guidelines](https://docs.langchain.com/oss/python/contributing/overview) for more. Additional guidelines: - Make sure optional dependencies are imported within a function. - Please do not add dependencies to `pyproject.toml` files (even optional ones) unless they are **required** for unit tests. - Most PRs should not touch more than one package. - Changes should be backwards compatible.
yindo added the pull-request label 2026-02-20 17:51:27 -05:00
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Reference: langchain-ai/langgraph#5257
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