fix(logging): prevent log file race condition under parallel attempts

[nuthalapativarun]

Summary

Fixes #1355.

When multiprocessing.Pool forks worker processes they inherit the parent's open FileHandler file descriptor. Concurrent writes — or reentrant flushes triggered by third-party library destructors (e.g. openai/httpcore closing connections in __del__) — on those shared handles cause a RuntimeError: reentrant call inside <_io.BufferedWriter> in Python 3.13+.

Fix: pass initializer=_worker_logging_init to Pool(...) in garak/probes/base.py. The initializer runs once in each worker process and:

1. Closes and removes every inherited log handler.
2. Re-opens a fresh FileHandler via logging.basicConfig, using the GARAK_LOG_FILE env var that garak/__init__.py already sets before any children are spawned.

Each worker then has its own private file descriptor pointing at the same log file, eliminating the shared-handle race.

Files changed

• garak/probes/base.py — add _worker_logging_init() and pass it as initializer to Pool

Test plan

• Reproduce with parallel_attempts: 2 and a multi-probe run (e.g. the config from the issue comments) — confirm no RuntimeError appears in the log
• Existing unit tests pass (pre-existing missing-module failures are unrelated to this change)

[aishwaryap]

The fix description appears promising but can we obtain:

1. A reproducible test that demonstrates that this fix resolves the error in question.
2. If a reproducible test can be found can that be converted into a unit / integration test

[aishwaryap]

See earlier comment

[nuthalapativarun]

Thanks for the clear feedback, @aishwaryap!

I've added tests/probes/test_probes_base_parallel_logging.py with six tests (latest commit 727728ba):

Unit tests for _worker_logging_init directly:

• test_worker_init_clears_inherited_handlers — verifies the initializer removes all inherited handlers (the root cause of the race)
• test_worker_init_opens_file_handler_when_env_set — verifies a fresh FileHandler is created pointing at GARAK_LOG_FILE
• test_worker_init_no_file_handler_when_env_unset — verifies no handler is added when the env var is absent
• test_worker_init_is_idempotent — verifies calling it twice doesn't accumulate duplicate handlers

Integration tests that exercise the actual Pool path:

• test_parallel_workers_log_without_error — spawns Pool(4) with _worker_logging_init, maps 8 worker tasks that each log 50 lines concurrently; asserts no RuntimeError is raised
• test_parallel_worker_fds_are_independent — verifies each worker's FileHandler has a different file descriptor than the parent's, confirming the shared-fd race is eliminated

All six pass locally. Let me know if you'd like any adjustments.