Reject nonpositive parallel worker counts

[IlyaKhalafi]

This PR fixes nonpositive worker counts waiting for a worker that was never started. With this, ParallelWorkerPool rejects them immediately with ValueError. This also applies to empty input. The public parallel=0 option still selects the CPU count.

Fixes #817.

12 focused tests, pre-commit and the CI mypy command passed. The existing early-close worker test was excluded because it also fails on upstream in this environment.

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 89b3c47f-6e0e-45ae-949d-bd107905f4b7

📥 Commits

Reviewing files that changed from the base of the PR and between f48af32 and 0220a20.

📒 Files selected for processing: 2

• fastembed/parallel_processor.py
• tests/test_parallel_processor.py

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📝 Walkthrough

ParallelWorkerPool.__init__ now raises ValueError when num_workers is zero or negative. Tests cover rejection of zero and negative values, and verify that worker counts of one and two preserve input order in ordered_map and leave pool.processes empty after iteration.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 0220a

Invalid worker counts now fail with ValueError before worker queues are allocated, while parallel=0 retains automatic CPU selection with a safe fallback. No material merge-blocking issue is established.

Pre-merge checks: 3 · 1 · 1

Failed checks: 1 warning · 1 inconclusive

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Linked Issues check		For #817, ParallelWorkerPool.__init__ raises ValueError for num_workers <= 0 before queue creation. The change also covers empty input because pool construction fails before iteration. Tests cov…	Provide reviewable evidence from the public embedding path or an automated test that parallel=0 resolves to a positive worker count.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: rejecting nonpositive parallel worker counts.
Description check		The description accurately explains the ValueError behavior, the empty-input case, the public parallel=0 behavior, linked issue, and validation performed.
Out of Scope Changes check		The changes are limited to the #817 validation and focused tests for invalid and positive worker counts. The tests verify error handling, ordered results, and process cleanup. No unrelated change is s…

Full details: Linked Issues check

Explanation

For #817, ParallelWorkerPool.__init__ raises ValueError for num_workers <= 0 before queue creation. The change also covers empty input because pool construction fails before iteration. Tests cover 0, -1, and -2. The available evidence does not establish that the public parallel=0 path still resolves to a positive CPU count.

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