harden directory removal for tests on Windows

Lib/test/support.py

--- a/Lib/test/support.py	Mon Jul 30 00:01:44 2012 +0200
+++ b/Lib/test/support.py	Thu Aug 02 08:43:32 2012 -0600
@@ -225,18 +225,79 @@
     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 i7@4.3GHz shows that usually only 1 iteration is
+        # required when contention occurs.
+        timeout = 0.001
+        while timeout < 1.0:
+            # Note we cannot use os.stat as it opens a handle to the pathname
+            # (if it has not already been removed) that we are waiting to
+            # remove, thus causing it to not be removed.
+            #
+            # Hence just use the contents of the directory for testing for
+            # existence.
+            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:
+        # The directory need not exist.
         if error.errno != errno.ENOENT:
             raise