Use multiprocessing.set_start_method("spawn") in conftest.py (very similar to pybind#4306, the only difference between the two PRs is the "spawn" vs "forkserver" argument).

Author: rwgk

tests/conftest.py

@@ -7,6 +7,8 @@
 import contextlib
 import difflib
 import gc
+import multiprocessing
+import os
 import re
 import textwrap
 
@@ -15,6 +17,9 @@
 # Early diagnostic for failed imports
 import pybind11_tests
 
+if os.name != "nt":
+    multiprocessing.set_start_method("spawn")
+
 _long_marker = re.compile(r"([0-9])L")
 _hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
 

tests/test_gil_scoped.py

@@ -154,8 +154,7 @@ def _run_in_process(target, *args, **kwargs):
         test_fn = args[0]
     # Do not need to wait much, 10s should be more than enough.
     timeout = 0.1 if test_fn is _intentional_deadlock else 10
-    mp_ctx = multiprocessing.get_context("spawn")
-    process = mp_ctx.Process(target=target, args=args, kwargs=kwargs)
+    process = multiprocessing.Process(target=target, args=args, kwargs=kwargs)
     process.daemon = True
     try:
         t_start = time.time()