Fix: eliminate Windows PID race condition by replacing concorekill.bat overwrite mechanism with safe PID registry (#391)

[GaneshPatil7517]

Problem

On Windows, concore.py wrote a single PID to concorekill.bat at module import time
using write mode ("w"). When multiple Python nodes launched simultaneously via
makestudy, each node overwrote the file — only the last node's PID survived.

This caused:

• Race condition: N-1 of N nodes became unkillable via concorekill.bat
• Stale PID danger: after a crash, the leftover file could contain a PID reassigned
  to an unrelated process, risking taskkill terminating the wrong program
• No cleanup: PID file persisted after node exit

Solution

Replaced the single-PID overwrite with an append-based PID registry system:

Before	After
concorekill.bat with one hardcoded taskkill line	concorekill_pids.txt registry (one PID per line, append mode)
Last writer wins	All nodes coexist safely
No exit cleanup	atexit handler removes current PID on shutdown
Blind taskkill	Generated concorekill.bat validates each PID via tasklist before killing

Key changes in concore.py:

• _register_pid() — appends current PID to concorekill_pids.txt
• _cleanup_pid() — removes current PID on exit; deletes both files when last node exits
• _write_kill_script() — generates concorekill.bat that checks each PID is a running Python process before issuing taskkill

Backward compatibility:

Users still run concorekill.bat exactly as before — no workflow change required.
Only Python layer modified; C++, MATLAB, and Verilog implementations are untouched.

Tests

Added 9 tests in TestPidRegistry:

• Registration creates file and appends (not overwrites)
• Cleanup removes only current PID, preserves others
• Last PID cleanup deletes both registry and kill script
• Missing registry handled gracefully (no crash)
• Kill script contains validation logic (tasklist + taskkill)
• Multi-node simulation (3+ PIDs coexist)
• Windows import-time registration

All 9 new tests pass. All pre-existing tests unaffected.

Fixes

Closes #391

[pradeeban]

@GaneshPatil7517 there is a merge conflict. Pls check.

[Copilot]

Pull request overview

This PR addresses Windows-specific reliability issues in concore.py by replacing the import-time “single PID overwrite” concorekill.bat mechanism with a multi-process PID registry and a regenerated kill script, aiming to eliminate PID overwrite races and reduce stale-PID risk.

Changes:

• Add a Windows PID registry (concorekill_pids.txt) with per-process registration and atexit cleanup.
• Generate a concorekill.bat script that iterates the registry and validates PIDs via tasklist before taskkill.
• Add a new test suite (TestPidRegistry) covering registration, cleanup behavior, and kill-script generation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
concore.py	Implements PID registry, kill script generation, and exit-time cleanup on Windows.
tests/test_concore.py	Adds tests validating registry behavior and generated kill script contents.

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[GaneshPatil7517]

hello @pradeeban Sir resolved merge conflict and the pr is ready to review please review it when you get the time...

[pradeeban]

@GaneshPatil7517 merge conflicts because I merged your other PR.

Also, this PR is crowded with too many irrelevant changes, like linechanges, removal of empty lines, etc. Such changes should not be in a PR. These are the changes that are causing merge conflicts. Please keep your PRs minimal.

Please create a new PR with just the minimal changes necessary.