Deflake Simple Cache backend on Windows.

net/disk_cache/simple/simple_util_win.cc

Index: net/disk_cache/simple/simple_util_win.cc
diff --git a/net/disk_cache/simple/simple_util_win.cc b/net/disk_cache/simple/simple_util_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a99b8c1f0025fcc64c31f85a79fc2c358b9289fa
--- /dev/null
+++ b/net/disk_cache/simple/simple_util_win.cc
@@ -0,0 +1,44 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/disk_cache/simple/simple_util.h"
+
+#include <windows.h>
+
+#include "base/files/file_util.h"
+#include "base/format_macros.h"
+#include "base/rand_util.h"
+#include "base/strings/stringprintf.h"
+#include "net/disk_cache/cache_util.h"
+
+namespace disk_cache {
+namespace simple_util {
+
+bool SimpleCacheDeleteFile(const base::FilePath& path) {
+  // Even if a file was opened with FLAG_SHARE_DELETE, it is not possible to
+  // create a new file with the same name until the original file is actually
+  // deleted. To allow new files to be created with the new name right away, we
+  // rename the file to a random name before deleting it.

[mmenke, 2014/10/28 23:58:36]

nit:  Don't use we in comments.

[gavinp, 2014/10/29 03:12:25]

Done.

+
+  // Why a random name? Because if the name was derived from our original name,
+  // then churn on a particular cache entry could cause flakey behaviour.

[mmenke, 2014/10/28 23:58:36]

Hrm...I'm not sure if I should whine about valid but less common (In chrome)
spellings here or not (x2).  :)

[gavinp, 2014/10/29 03:12:25]

In the library in the Cambridge office, there's a copy of a very good English
dictionary, the "Oxford Canadian English Dictionary." When I look up "behavior"
in it, it says: "variant, chiefly American, of behaviour."

+
+  // TODO(gaivnp): Ensure we clean up these "todelete_" files on periodic

[mmenke, 2014/10/28 23:58:36]

nit:  Don't use we.

[gavinp, 2014/10/29 03:12:25]

Done.

+  // directory sweeps.
+  const base::FilePath rename_target =
+      path.DirName().AppendASCII(base::StringPrintf("todelete_%016" PRIx64,
+                                                    base::RandUint64()));
+
+  const bool rename_succeeded = MoveFile(path.value().c_str(),

[mmenke, 2014/10/28 23:58:36]

Or if I should whine about the bonus consts, which are even less common in the
Chrome code base.

[gavinp, 2014/10/29 03:12:25]

This is a challenging call. The rule in our coding standard is vague beyond
comprehension: "Use const whenever it makes sense." (well, that really helps).

I have removed this use of const; you're right that it's inconsistent.

+                                         rename_target.value().c_str());
+  if (rename_succeeded)
+    return DeleteCacheFile(rename_target);
+
+  // The rename did not succeed, so we will fall back to deleting the file in
+  // place, which might cause some flake.

[mmenke, 2014/10/28 23:58:36]

nit:  Don't use we in comments.

[gavinp, 2014/10/29 03:12:25]

Done.

+  return DeleteCacheFile(path);
+}
+
+}  // namespace simple_util
+}  // namespace disk_cache