[Fix] propagate init_function errors from all MPI ranks in block allocation mode

[jan-janssen]

Summary

• In interactive_parallel.py, the init_function branch only reported errors from MPI rank 0; failures on non-zero ranks were silently swallowed, leaving those ranks with uninitialised memory. Subsequent function calls on the affected ranks would then receive wrong or missing kwargs injected from memory.
• The fix gathers errors from all ranks via MPI.COMM_WORLD.gather before rank 0 sends the success/error response to the scheduler — mirroring how function-execution results are already gathered. This also acts as an implicit barrier so the scheduler cannot dispatch the next task until every rank has finished initialising.
• Adds test_internal_memory_mpi to cover block_allocation + cores=2 + init_function, a combination that had zero test coverage.

Test plan

• Existing test test_internal_memory (cores=1) continues to pass
• New test test_internal_memory_mpi (cores=2) passes and verifies that both MPI ranks receive the memory value set by the init function
• Full test suite green

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Enhanced error handling during initialization to capture errors across distributed execution ranks and provide clearer error reporting.

• Tests

  • Added test coverage for memory allocation behavior in parallel execution environments.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 911eeadf-d364-4fb7-bc73-75d21bef6094

📥 Commits

Reviewing files that changed from the base of the PR and between b173e16 and 7f56240.

📒 Files selected for processing (1)

• src/executorlib/backend/interactive_parallel.py

📝 Walkthrough

Walkthrough

The "init" handling in interactive_parallel.py is refactored to catch exceptions into init_error, gather that variable across all MPI ranks, and have rank zero select and forward the first non-None error via ZMQ. A new unit test (test_internal_memory_mpi) validates init_function memory sharing with cores=2 using mpi4py.

Changes

MPI Init Error Propagation

Layer / File(s)	Summary
Gather init errors across MPI ranks and report on rank zero src/executorlib/backend/interactive_parallel.py, tests/unit/standalone/interactive/test_spawner.py	The "init" path now catches exceptions into init_error, gathers it across ranks (or wraps in a list for single-rank runs), and rank zero picks the first non-None error to send via ZMQ and write the error file; the new test_internal_memory_mpi test, gated on mpi4py, verifies init_function with cores=2 returns two matching NumPy arrays.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• pyiron/executorlib#804: Introduced the "fail safe init function" logic in the same "init" handling path of interactive_parallel.py that this PR extends with cross-rank error gathering.

Poem

🐇 Across the MPI ranks I hop,
Collecting errors, none shall drop.
Rank zero picks the first mistake,
And sends it back for the caller's sake.
No init error slips away—
The rabbit gathers them all today! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% 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
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and specifically describes the main change: propagating init_function errors from all MPI ranks in block allocation mode, which matches the core objective of the PR.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/init-function-mpi-parallel-block-allocation

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.84%. Comparing base (640e440) to head (7f56240).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/executorlib/backend/interactive_parallel.py	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1023      +/-   ##
==========================================
- Coverage   94.24%   93.84%   -0.40%     
==========================================
  Files          39       39              
  Lines        2119     2128       +9     
==========================================
  Hits         1997     1997              
- Misses        122      131       +9     

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