ib.collect support wait_for_inputs option

[ian-Liaozy]

Fixes #37220

This PR updates interactive_beam.collect() to correctly handle PCollections that depend on asynchronously running background caching jobs.

Previously, if a user attempted to collect() a PCollection while its upstream dependencies were still being computed/cached by the background RecordingManager, the result could be incomplete or trigger race conditions.

This change introduces a wait_for_inputs parameter (defaulting to True) which ensures that collect() blocks until all necessary upstream dependencies have finished their background computation.

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Summary of Changes

Hello @ian-Liaozy, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement to the ib.collect function within Apache Beam's Interactive Runner by adding a wait_for_inputs parameter. This parameter provides users with fine-grained control over how collect handles asynchronous dependencies, allowing them to optimize for either immediate scheduling or guaranteed completion of upstream computations, thereby influencing the execution flow and potential resource utilization of interactive Beam pipelines.

Highlights

• New wait_for_inputs option for ib.collect: The collect function in interactive_beam.py now accepts a wait_for_inputs boolean parameter, defaulting to True.
• Control over asynchronous dependencies: This new option allows users to specify whether collect should wait for upstream asynchronous computations to complete before proceeding.
• Performance implications: Setting wait_for_inputs to False can schedule computations immediately but might lead to redundant pipeline stage executions if dependencies are not yet ready.
• Comprehensive testing: New unit tests have been added to interactive_beam_test.py to ensure the correct behavior of collect with different wait_for_inputs values.

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R: @damccorm for label python.

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[damccorm]

Could you help me understand what use case you're trying to solve for here? If I'm reading the PR right, you're not changing the default behavior, but you are letting the recording manager get into a potentially bad state if the user intentionally sets wait_for_inputs to false. Its not clear to me why this is desireable

[ian-Liaozy]

Hi Danny, my thinking here is:

1. Previously, ib.collect() will not automatically wait for background caching job to finish. If a user ran collect() on a PCollection whose dependencies were still computing, they could get empty or partial results without warning.
2. By defaulting wait_for_inputs=True, we ensure the standard user experience is consistent: we always wait for upstream dependencies to finish before collecting. Also, adding wait_for_inputs option will align with current implementation for ib.compute()
3. Back to the exact code block that you are quoting, the 'bad state' happens when user decide to set wait_for_inputs=False, explicitly request to bypass the safety checks and synchronization. My thinking is it will delegate the failure handling to actual pipeline execution, which seems acceptable

[damccorm]

By defaulting wait_for_inputs=True, we ensure the standard user experience is consistent: we always wait for upstream dependencies to finish before collecting. Also, adding wait_for_inputs option will align with current implementation for ib.compute()

We are not changing the default behavior in this PR. So I don't think this is doing what you think it is doing.

Back to the exact code block that you are quoting, the 'bad state' happens when user decide to set wait_for_inputs=False, explicitly request to bypass the safety checks and synchronization. My thinking is it will delegate the failure handling to actual pipeline execution, which seems acceptable

When is this desirable? It seems like it is always a bad outcome