test: use baseline thread detection for Windows cleanup

Instead of matching thread names (which was unreliable), capture the
baseline set of threads before starting proxy.py and wait until all
extra threads have finished.

Author: rodrigo.nogueira

tests/test_proxy_functional.py

@@ -66,6 +66,13 @@ def secure_proxy_url(tls_certificate_pem_path: str) -> Iterator[URL]:
 
     This fixture also spawns that instance and tears it down after the test.
     """
+    if os.name == "nt":
+        import gc
+        import threading
+        import time
+
+        baseline_threads = set(threading.enumerate())
+
     proxypy_args = [
         # --threadless does not work on windows, see
         # https://github.com/abhinavsingh/proxy.py/issues/492
@@ -83,26 +90,21 @@ def secure_proxy_url(tls_certificate_pem_path: str) -> Iterator[URL]:
     ]
 
     with proxy.Proxy(input_args=proxypy_args) as proxy_instance:
+        if os.name == "nt":
+            spawned_threads = set(threading.enumerate()) - baseline_threads
+
         yield URL.build(
             scheme="https",
             host=str(proxy_instance.flags.hostname),
             port=proxy_instance.flags.port,
         )
 
     if os.name == "nt":
-        import gc
-        import threading
-        import time
-
         deadline = time.monotonic() + 5.0
         while time.monotonic() < deadline:
             gc.collect()
-            proxy_threads = [
-                t
-                for t in threading.enumerate()
-                if "proxy" in t.name.lower() or "acceptor" in t.name.lower()
-            ]
-            if not proxy_threads:
+            remaining = set(threading.enumerate()).intersection(spawned_threads)
+            if not remaining:
                 break
             time.sleep(0.05)