gh-87135: Hang non-main threads that attempt to acquire the GIL during finalization (GH-105805)

Instead of surprise crashes and memory corruption, we now hang threads that attempt to re-enter the Python interpreter after Python runtime finalization has started. These are typically daemon threads (our long standing mis-feature) but could also be threads spawned by extension modules that then try to call into Python. This marks the `PyThread_exit_thread` public C API as deprecated as there is no plausible safe way to accomplish that on any supported platform in the face of things like C++ code with finalizers anywhere on a thread's stack. Doing this was the least bad option.

Co-authored-by: Gregory P. Smith <greg@krypto.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/Python/thread_nt.h b/Python/thread_nt.h
index 4256581..3a01a7f 100644
--- a/Python/thread_nt.h
+++ b/Python/thread_nt.h
@@ -291,6 +291,14 @@ PyThread_exit_thread(void)
     _endthreadex(0);
 }
 
+void _Py_NO_RETURN
+PyThread_hang_thread(void)
+{
+    while (1) {
+        SleepEx(INFINITE, TRUE);
+    }
+}
+
 /*
  * Lock support. It has to be implemented as semaphores.
  * I [Dag] tried to implement it with mutex but I could find a way to