pythongh-98360: multiprocessing now spawns children on Windows with correct argv[0] in virtual environments

Author: zooba

Lib/test/_test_venv_multiprocessing.py

@@ -0,0 +1,40 @@
+import multiprocessing
+import random
+import sys
+import time
+
+def fill_queue(queue, code):
+    queue.put(code)
+
+
+def drain_queue(queue, code):
+    if code != queue.get():
+        sys.exit(1)
+
+
+def test_func():
+    code = random.randrange(0, 1000)
+    queue = multiprocessing.Queue()
+    fill_pool = multiprocessing.Process(
+        target=fill_queue,
+        args=(queue, code)
+    )
+    drain_pool = multiprocessing.Process(
+        target=drain_queue,
+        args=(queue, code)
+    )
+    drain_pool.start()
+    fill_pool.start()
+    fill_pool.join()
+    drain_pool.join()
+
+
+def main():
+    test_pool = multiprocessing.Process(target=test_func)
+    test_pool.start()
+    test_pool.join()
+    sys.exit(test_pool.exitcode)
+
+
+if __name__ == "__main__":
+    main()

Misc/NEWS.d/next/Windows/2022-10-19-20-00-28.gh-issue-98360.O2m6YG.rst

@@ -0,0 +1,4 @@
+Fixes :mod:`multiprocessing` spawning child processes on Windows from a
+virtual environment to ensure that child processes that also use
+:mod:`multiprocessing` to spawn more children will recognize that they are
+in a virtual environment.