Kill individual worker process after timeout in test_build_meta

According to the Python docs, shutting down the process pool does not
terminate the tasks that are already running, so it is necessary to
manually kill the individual processes in the pool.

Author: abravalheri

setuptools/tests/test_build_meta.py

@@ -1,7 +1,9 @@
 import os
 import shutil
+import signal
 import tarfile
 import importlib
+import contextlib
 from concurrent import futures
 import re
 
@@ -34,15 +36,23 @@ def __getattr__(self, name):
         def method(*args, **kw):
             root = os.path.abspath(self.cwd)
             caller = BuildBackendCaller(root, self.env, self.backend_name)
-            task = self.pool.submit(caller, name, *args, **kw)
+            pid = None
             try:
-                return task.result(TIMEOUT)
+                pid = self.pool.submit(os.getpid).result(TIMEOUT)
+                return self.pool.submit(caller, name, *args, **kw).result(TIMEOUT)
             except futures.TimeoutError:
-                self.pool.shutdown(wait=False)
+                self.pool.shutdown(wait=False)  # doesn't stop already running processes
+                self._kill(pid)
                 pytest.xfail(f"Backend did not respond before timeout ({TIMEOUT} s)")
 
         return method
 
+    def _kill(self, pid):
+        if pid is None:
+            return
+        with contextlib.suppress(ProcessLookupError):
+            os.kill(pid, signal.SIGKILL)
+
 
 class BuildBackendCaller(BuildBackendBase):
     def __init__(self, *args, **kwargs):