Make our Python Altair code thread-safe #12673
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Pull Request Overview
This PR makes Streamlit's Altair chart handling code thread-safe by wrapping thread-unsafe operations in a threading lock. The main issue addressed is that Altair's global variables for themes and data transformers were being modified concurrently, causing empty charts when multiple charts were rendered simultaneously in different threads.
- Introduces a threading lock to protect Altair global state modifications
- Refactors the data transformer function to be a standalone module-level function
- Updates comments to reflect the new transformer function name
kmcgrady
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Things LGTM overall. I agree with testing. I remember we had some e2e tests failing likely due to this scenario, but we must have found a workaround on the tests. We do mark some as flaky so perhaps we can test drive removing it, but that seems like a separate initiative.
Co-authored-by: Copilot <[email protected]>
Describe your changes
Today, our Altair-handling code in Python does some things that modify global variables in the
altairmodule differently for each chart, which makes the code thead-unsafe. This leads to empty charts whenever two charts are drawn at the same time in different threads.This PR addresses that by wrapping the thread-unsafe code into a
threading.Lock, plus a couple of small refactors.GitHub Issue Link (if applicable)
none
Testing Plan
Unit Tests (JS and/or Python)E2E TestsAny manual testing needed?Contribution License Agreement
By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.