Fix hybrid scan reader state not fully reset for multi-threaded reuse

[Deegue]

Description

hybrid_scan_reader_impl::reset_internal_state() was not resetting _output_chunk_produced and the three column selection flags (_is_filter_columns_selected, _is_payload_columns_selected, _is_all_columns_selected). When a reader instance is reused across multiple threads, stale state from a previous read carries over:

• _output_chunk_produced being true causes is_first_output_chunk() to incorrectly return false
• Column selection flags being true triggers early-return guards in select_all_columns() / select_filter_columns() / select_payload_columns(), skipping column setup entirely

This patch adds the missing resets to reset_internal_state().

closes #22851

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between b969a3a and 3a9b1e6.

📒 Files selected for processing (1)

• cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp

🚧 Files skipped from review as they are similar to previous changes (1)

• cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved Parquet reading reliability by ensuring reader state is consistently reset between operations, preventing intermittent inconsistencies in data chunking and retrieval and reducing unexpected empty or partial result chunks.

Walkthrough

Adds explicit resets in hybrid_scan_reader_impl::reset_internal_state(): sets _output_chunk_produced = false and clears _is_filter_columns_selected, _is_payload_columns_selected, and _is_all_columns_selected to ensure a consistent baseline for subsequent reads.

Changes

Hybrid Scan Reader State Reset

Layer / File(s)	Summary
Complete internal state reset cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp	reset_internal_state() now sets _output_chunk_produced to false and clears _is_filter_columns_selected, _is_payload_columns_selected, and _is_all_columns_selected immediately after resetting _expr_conv and _mr, ensuring the reader does not carry stale flags across reuses.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• rapidsai/cudf#22716: Both PRs modify hybrid_scan_reader_impl::reset_internal_state() and related _output_chunk_produced handling.

Suggested labels

bug, non-breaking

Suggested reviewers

• mhaseeb123

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing incomplete state reset in hybrid scan reader for multi-threaded reuse scenarios.
Description check	✅ Passed	The description is directly related to the changeset, explaining the bug, the issue it causes, and how the patch addresses it.
Linked Issues check	✅ Passed	The PR directly addresses the objectives in issue #22851 by adding the missing resets for _output_chunk_produced and the three column selection flags to reset_internal_state().
Out of Scope Changes check	✅ Passed	All changes are scoped to the reset_internal_state() function as required by issue #22851, with no extraneous modifications.

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🧪 Generate unit tests (beta)

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[rjzamora]

Thank you for the contribution @Deegue

@mhaseeb123 - Do you have time to look at this?

[mhaseeb123]

Please use the reader->reset_column_selection() API instead. See #22851 (comment)