Suspend Python threads before fork() by youknowone · Pull Request #7364 · RustPython/RustPython

* Suspend Python threads before fork()

Add stop-the-world thread suspension around fork() to prevent
deadlocks from locks held by dead parent threads in the child.

- Thread states: DETACHED / ATTACHED / SUSPENDED with atomic CAS
  transitions matching _PyThreadState_{Attach,Detach,Suspend}
- stop_the_world / start_the_world: park all non-requester threads
  before fork, resume after (parent) or reset (child)
- allow_threads (Py_BEGIN/END_ALLOW_THREADS): detach around blocking
  syscalls (os.read/write, waitpid, Lock.acquire, time.sleep) so
  stop_the_world can force-park via CAS
- Acquire/release import lock around fork lifecycle
- zero_reinit_after_fork: generic lock reset for parking_lot types
- gc_clear_raw: detach dict instead of clearing entries
- Lock-free double-check for descriptor cache reads (no read-side
  seqlock); write-side seqlock retained for writer serialization
- fork() returns PyResult, checks PythonFinalizationError, calls
  sys.audit

* Suspend Python threads before fork()

Add stop-the-world thread suspension around fork() to prevent
deadlocks from locks held by dead parent threads in the child.

- Thread states: DETACHED / ATTACHED / SUSPENDED with atomic CAS
  transitions matching _PyThreadState_{Attach,Detach,Suspend}
- stop_the_world / start_the_world: park all non-requester threads
  before fork, resume after (parent) or reset (child)
- allow_threads (Py_BEGIN/END_ALLOW_THREADS): detach around blocking
  syscalls (os.read/write, waitpid, Lock.acquire, time.sleep) so
  stop_the_world can force-park via CAS
- Acquire/release import lock around fork lifecycle
- zero_reinit_after_fork: generic lock reset for parking_lot types
- gc_clear_raw: detach dict instead of clearing entries
- Lock-free double-check for descriptor cache reads (no read-side
  seqlock); write-side seqlock retained for writer serialization
- fork() returns PyResult, checks PythonFinalizationError, calls
  sys.audit