Address the review

Name the lock files, so that it is clear what left them in the temporary
directory, and say why they are left.  Close the file descriptor whatever
goes wrong.  Call the resource of bigmem tests 'bigmem'.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/support/__init__.py

@@ -339,7 +339,8 @@ def get_resource_value(resource):
 
 # Resources which are machine-wide: two tests using one of them at the same
 # time interfere with each other.
-EXCLUSIVE_RESOURCES = frozenset({'audio', 'console', 'curses', 'gui'})
+EXCLUSIVE_RESOURCES = frozenset({'audio', 'bigmem', 'console', 'curses',
+                                 'gui'})
 
 # The environment variable naming the directory in which the test runner keeps
 # the lock files.  It is set only when tests are run in parallel.
@@ -359,7 +360,7 @@ def _lock_file(fd):
             try:
                 msvcrt.locking(fd, msvcrt.LK_NBLCK, 1)
             except OSError:
-                # LK_LOCK gives up after ten seconds, so retry ourselves.
+                # It returns at once if the file is locked, so wait ourselves.
                 time.sleep(0.1)
             else:
                 return
@@ -377,16 +378,22 @@ def _open_exclusive_lock(resource):
     if not directory:
         # The tests are not run in parallel, so there is nothing to exclude.
         return None
+    # The file is left behind: another process may be waiting on a lock on it,
+    # and it is empty anyway.
+    path = os.path.join(directory, f'python-test-exclusive-{resource}.lock')
     try:
-        fd = os.open(os.path.join(directory, f'exclusive-{resource}.lock'),
-                     os.O_WRONLY | os.O_CREAT, 0o600)
+        fd = os.open(path, os.O_WRONLY | os.O_CREAT, 0o600)
     except OSError:
         return None
     try:
         _lock_file(fd)
-    except OSError:
+    except (ImportError, OSError):
+        # Locking is not available here, so the tests are not serialized.
         os.close(fd)
         return None
+    except BaseException:
+        os.close(fd)
+        raise
     return fd
 
 
@@ -1454,7 +1461,7 @@ def wrapper(self):
                 cls = type(self)
                 qualname = f'{cls.__qualname__}.{f.__name__}'
                 # A real run allocates most of the memory of the machine.
-                with _exclusive_resource('memory'):
+                with _exclusive_resource('bigmem'):
                     proc = isolation._start_test(cls.__module__, qualname)
                     watchdog = _memory_watchdog(proc.pid) if verbose else None
                     payload, output, returncode = proc.wait(tick=watchdog)