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GuardObjects.h
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GuardObjects.h
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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim: set ts=8 sw=4 et tw=99 ft=cpp: */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is mozilla.org code.
*
* The Initial Developer of the Original Code is
* the Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2010
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* L. David Baron <dbaron@dbaron.org>, Mozilla Corporation (original author)
* Ms2ger <ms2ger@gmail.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
/* Implementation of macros to ensure correct use of RAII Auto* objects. */
#ifndef mozilla_GuardObjects_h
#define mozilla_GuardObjects_h
#include "mozilla/Assertions.h"
#include "mozilla/Types.h"
#ifdef __cplusplus
#ifdef DEBUG
namespace mozilla {
namespace detail {
/*
* The following classes are designed to cause assertions to detect
* inadvertent use of guard objects as temporaries. In other words,
* when we have a guard object whose only purpose is its constructor and
* destructor (and is never otherwise referenced), the intended use
* might be:
*
* AutoRestore savePainting(mIsPainting);
*
* but is is easy to accidentally write:
*
* AutoRestore(mIsPainting);
*
* which compiles just fine, but runs the destructor well before the
* intended time.
*
* They work by adding (#ifdef DEBUG) an additional parameter to the
* guard object's constructor, with a default value, so that users of
* the guard object's API do not need to do anything. The default value
* of this parameter is a temporary object. C++ (ISO/IEC 14882:1998),
* section 12.2 [class.temporary], clauses 4 and 5 seem to assume a
* guarantee that temporaries are destroyed in the reverse of their
* construction order, but I actually can't find a statement that that
* is true in the general case (beyond the two specific cases mentioned
* there). However, it seems to be true.
*
* These classes are intended to be used only via the macros immediately
* below them:
*
* MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER declares (ifdef DEBUG) a member
* variable, and should be put where a declaration of a private
* member variable would be placed.
* MOZ_GUARD_OBJECT_NOTIFIER_PARAM should be placed at the end of the
* parameters to each constructor of the guard object; it declares
* (ifdef DEBUG) an additional parameter. (But use the *_ONLY_PARAM
* variant for constructors that take no other parameters.)
* MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL should likewise be used in
* the implementation of such constructors when they are not inline.
* MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT should be used in
* the implementation of such constructors to pass the parameter to
* a base class that also uses these macros
* MOZ_GUARD_OBJECT_NOTIFIER_INIT is a statement that belongs in each
* constructor. It uses the parameter declared by
* MOZ_GUARD_OBJECT_NOTIFIER_PARAM.
*
* For more details, and examples of using these macros, see
* https://developer.mozilla.org/en/Using_RAII_classes_in_Mozilla
*/
class MOZ_EXPORT_API(GuardObjectNotifier)
{
private:
bool* statementDone;
public:
GuardObjectNotifier() : statementDone(NULL) {}
~GuardObjectNotifier() {
*statementDone = true;
}
void setStatementDone(bool* statementIsDone) {
statementDone = statementIsDone;
}
};
class MOZ_EXPORT_API(GuardObjectNotificationReceiver)
{
private:
bool statementDone;
public:
GuardObjectNotificationReceiver() : statementDone(false) {}
~GuardObjectNotificationReceiver() {
/*
* Assert that the guard object was not used as a temporary.
* (Note that this assert might also fire if init is not called
* because the guard object's implementation is not using the
* above macros correctly.)
*/
MOZ_ASSERT(statementDone);
}
void init(const GuardObjectNotifier& constNotifier) {
/*
* constNotifier is passed as a const reference so that we can pass a
* temporary, but we really intend it as non-const.
*/
GuardObjectNotifier& notifier = const_cast<GuardObjectNotifier&>(constNotifier);
notifier.setStatementDone(&statementDone);
}
};
} /* namespace detail */
} /* namespace mozilla */
#endif /* DEBUG */
#ifdef DEBUG
# define MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER \
mozilla::detail::GuardObjectNotificationReceiver _mCheckNotUsedAsTemporary;
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM \
, const mozilla::detail::GuardObjectNotifier& _notifier = \
mozilla::detail::GuardObjectNotifier()
# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM \
const mozilla::detail::GuardObjectNotifier& _notifier = \
mozilla::detail::GuardObjectNotifier()
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL \
, const mozilla::detail::GuardObjectNotifier& _notifier
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT \
, _notifier
# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT \
_notifier
# define MOZ_GUARD_OBJECT_NOTIFIER_INIT \
do { _mCheckNotUsedAsTemporary.init(_notifier); } while (0)
#else
# define MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM
# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL
# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT
# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT
# define MOZ_GUARD_OBJECT_NOTIFIER_INIT do { } while (0)
#endif
#endif /* __cplusplus */
#endif /* mozilla_GuardObjects_h */