Fix #15496. Add directory removal helpers to make Windows tests more …

…reliable. Patch by Jeremy Kloth

Lib/test/support.py

@@ -200,17 +200,81 @@ def unload(name):
     except KeyError:
         pass
 
+if sys.platform.startswith("win"):
+    def _waitfor(func, pathname, waitall=False):
+        # Peform the operation
+        func(pathname)
+        # Now setup the wait loop
+        if waitall:
+            dirname = pathname
+        else:
+            dirname, name = os.path.split(pathname)
+            dirname = dirname or '.'
+        # Check for `pathname` to be removed from the filesystem.
+        # The exponential backoff of the timeout amounts to a total
+        # of ~1 second after which the deletion is probably an error
+        # anyway.
+        # Testing on a [email protected] shows that usually only 1 iteration is
+        # required when contention occurs.
+        timeout = 0.001
+        while timeout < 1.0:
+            # Note we are only testing for the existance of the file(s) in
+            # the contents of the directory regardless of any security or
+            # access rights.  If we have made it this far, we have sufficient
+            # permissions to do that much using Python's equivalent of the
+            # Windows API FindFirstFile.
+            # Other Windows APIs can fail or give incorrect results when
+            # dealing with files that are pending deletion.
+            L = os.listdir(dirname)
+            if not (L if waitall else name in L):
+                return
+            # Increase the timeout and try again
+            time.sleep(timeout)
+            timeout *= 2
+        warnings.warn('tests may fail, delete still pending for ' + pathname,
+                      RuntimeWarning, stacklevel=4)
+
+    def _unlink(filename):
+        _waitfor(os.unlink, filename)
+
+    def _rmdir(dirname):
+        _waitfor(os.rmdir, dirname)
+
+    def _rmtree(path):
+        def _rmtree_inner(path):
+            for name in os.listdir(path):
+                fullname = os.path.join(path, name)
+                if os.path.isdir(fullname):
+                    _waitfor(_rmtree_inner, fullname, waitall=True)
+                    os.rmdir(fullname)
+                else:
+                    os.unlink(fullname)
+        _waitfor(_rmtree_inner, path, waitall=True)
+        _waitfor(os.rmdir, path)
+else:
+    _unlink = os.unlink
+    _rmdir = os.rmdir
+    _rmtree = shutil.rmtree
+
 def unlink(filename):
     try:
-        os.unlink(filename)
+        _unlink(filename)
     except OSError as error:
         # The filename need not exist.
         if error.errno not in (errno.ENOENT, errno.ENOTDIR):
             raise
 
+def rmdir(dirname):
+    try:
+        _rmdir(dirname)
+    except OSError as error:
+        # The directory need not exist.
+        if error.errno != errno.ENOENT:
+            raise
+
 def rmtree(path):
     try:
-        shutil.rmtree(path)
+        _rmtree(path)
     except OSError as error:
         # Unix returns ENOENT, Windows returns ESRCH.
         if error.errno not in (errno.ENOENT, errno.ESRCH):

Misc/NEWS

@@ -413,6 +413,9 @@ Extension Modules
 Tests
 -----
 
+- Issue #15496: Add directory removal helpers for tests on Windows.
+  Patch by Jeremy Kloth.
+
 - Issue #15467: Move helpers for __sizeof__ tests into test_support.
   Patch by Serhiy Storchaka.