ian-Liaozy opened a new pull request, #39161:
URL: https://github.com/apache/beam/pull/39161
This PR resolves several critical caching issues in Interactive Beam when
executing pipelines in notebook environments (like Colab), preventing
deadlocks, duplicate execution of runner jobs, and stale dependency resolution.
### Changes:
1. **Fix Background Thread Deadlock**:
Updated `_wait_for_dependencies` to skip checking the target PCollection
itself when executing inside the background thread (indicated by the presence
of `async_result`). This avoids a self-deadlock where the background thread
blocked waiting for its own future to resolve.
2. **Fix Wait Race Condition**:
Previously, calling `future.result()` in `_wait_for_dependencies` was
insufficient because the future resolves *before* the `_on_done` callback
finishes executing to mark the PCollection as computed. This created a race
condition where the main thread resumed, saw the PCollection was still
"uncomputed", and started a duplicate execution job.
We resolved this by introducing a `threading.Event` (`_completed_event`)
in `AsyncComputationResult` that is set at the very end of `_on_done`. The main
thread now blocks on `comp.wait_for_completion()`, guaranteeing that it only
continues after the PCollection is fully marked as computed.
3. **Recalculate Uncomputed PCollections**:
Updated `record()` to recalculate the subset of remaining uncomputed
PCollections *after* the dependency wait completes. If a PCollection finished
computing during the wait, it skips the duplicate fragment execution.
4. **Fix Stale Pipeline Graph**:
Removed caching of the `PipelineGraph` in `RecordingManager`. Re-creating
the graph dynamically ensures that any new transforms added by users in
subsequent notebook cells are correctly detected and resolved as dependencies.
5. **Unit Tests Added**:
Added three new tests to `recording_manager_test.py` covering:
- Deadlock avoidance and waiting behavior depending on `async_result`.
- Dynamic recreation of the `PipelineGraph` when new transforms are
appended.
- Recalculation of uncomputed PCollections in `record()` after wait
completion.
------------------------
fixes #37220
------------------------
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