Fix double-initialization of CComModule.

base/win/atl_module.h

+// Copyright (c) 2011 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.
+
+#ifndef BASE_WIN_ATL_MODULE_H_
+#define BASE_WIN_ATL_MODULE_H_
+#pragma once
+
+#include <atlbase.h>
+#include <atlcom.h>
+
+namespace base {
+namespace win {
+
+// Ensure that we have exactly one ATL module registered. It's safe to
+// call this more than once. ATL functions will crash if there's no
+// ATL module registered, or if you try to register two of them, so
+// dynamically registering one if needed makes it much easier for us
+// to support different build configurations like multi-dll without
+// worrying about which side of a module boundary each ATL module object
+// belongs on.
+//
+// This function must be implemented in this header file rather than a
+// source file so that it's inlined into the module where it's included,
+// rather than in the "base" module.
+static void CreateATLModuleIfNeeded() {
+  if (_pAtlModule == NULL) {
+    // This creates the module and automatically updates _pAtlModule.
+    static CComModule module;

[Nico, 2011/11/09 18:00:57]

This adds an exit time destructor. Use CR_DEFINE_STATIC_LOCAL instead.

Also, I'm not sure if a static variable in a static function will refer to the
same object in all translation units if the function is not marked as "inline"
("A static local variable in an extern inline function always refers to the same
object.", but nothing about static locals in static functions; 7.1.2.-4-) – I'd
put the function definition into a cc file for that reason

[dmazzoni, 2011/11/09 18:21:04]

The destructor needs to be called, or CComModule can't clean up its state, i.e.
cleanly terminate connections with other processes.
Putting in in a .cc file wouldn't work, the whole reason we need this is so that
in a multi-dll build, every dll that needs it gets an ATL module.

There are no other translation units that will need to access this variable. The
CComModule constructor sets a global variable _pAtlModule and points it to this
object. As soon as one CComModule is registered for that dll, any time this
function is executed again the conditional will fail and the static local will
never be constructed in the first place.

[Nico, 2011/11/09 18:37:22]

I'm currently trying to remove all exit time destructors from the code base.
Exit time destructors in base/ will become a compiler error today. (in ui/ too.)

Can you add an explicit DestroyATLModule() call or something like that?
Ah! This might deserve a comment.
What if multiple threads call this function at the same time?

[Nico, 2011/11/09 18:47:18]

(The error part is actually only true for platforms where we build with clang,
i.e. mac, linux, and chromeos. But windows will join that list eventually.)

+  }
+}
+
+}  // namespace win
+}  // namespace base
+
+#endif  // BASE_WIN_ATL_MODULE_H_