michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /* Implementation of macros to ensure correct use of RAII Auto* objects. */
michael@0: 
michael@0: #ifndef mozilla_GuardObjects_h
michael@0: #define mozilla_GuardObjects_h
michael@0: 
michael@0: #include "mozilla/Assertions.h"
michael@0: #include "mozilla/NullPtr.h"
michael@0: #include "mozilla/Types.h"
michael@0: 
michael@0: #ifdef __cplusplus
michael@0: 
michael@0: #ifdef DEBUG
michael@0: 
michael@0: namespace mozilla {
michael@0: namespace detail {
michael@0: 
michael@0: /*
michael@0:  * The following classes are designed to cause assertions to detect
michael@0:  * inadvertent use of guard objects as temporaries. In other words,
michael@0:  * when we have a guard object whose only purpose is its constructor and
michael@0:  * destructor (and is never otherwise referenced), the intended use
michael@0:  * might be:
michael@0:  *
michael@0:  *   AutoRestore savePainting(mIsPainting);
michael@0:  *
michael@0:  * but is is easy to accidentally write:
michael@0:  *
michael@0:  *   AutoRestore(mIsPainting);
michael@0:  *
michael@0:  * which compiles just fine, but runs the destructor well before the
michael@0:  * intended time.
michael@0:  *
michael@0:  * They work by adding (#ifdef DEBUG) an additional parameter to the
michael@0:  * guard object's constructor, with a default value, so that users of
michael@0:  * the guard object's API do not need to do anything. The default value
michael@0:  * of this parameter is a temporary object. C++ (ISO/IEC 14882:1998),
michael@0:  * section 12.2 [class.temporary], clauses 4 and 5 seem to assume a
michael@0:  * guarantee that temporaries are destroyed in the reverse of their
michael@0:  * construction order, but I actually can't find a statement that that
michael@0:  * is true in the general case (beyond the two specific cases mentioned
michael@0:  * there). However, it seems to be true.
michael@0:  *
michael@0:  * These classes are intended to be used only via the macros immediately
michael@0:  * below them:
michael@0:  *
michael@0:  *   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER declares (ifdef DEBUG) a member
michael@0:  *     variable, and should be put where a declaration of a private
michael@0:  *     member variable would be placed.
michael@0:  *   MOZ_GUARD_OBJECT_NOTIFIER_PARAM should be placed at the end of the
michael@0:  *     parameters to each constructor of the guard object; it declares
michael@0:  *     (ifdef DEBUG) an additional parameter. (But use the *_ONLY_PARAM
michael@0:  *     variant for constructors that take no other parameters.)
michael@0:  *   MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL should likewise be used in
michael@0:  *     the implementation of such constructors when they are not inline.
michael@0:  *   MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT should be used in
michael@0:  *     the implementation of such constructors to pass the parameter to
michael@0:  *     a base class that also uses these macros
michael@0:  *   MOZ_GUARD_OBJECT_NOTIFIER_INIT is a statement that belongs in each
michael@0:  *     constructor. It uses the parameter declared by
michael@0:  *     MOZ_GUARD_OBJECT_NOTIFIER_PARAM.
michael@0:  *
michael@0:  * For more details, and examples of using these macros, see
michael@0:  * https://developer.mozilla.org/en/Using_RAII_classes_in_Mozilla
michael@0:  */
michael@0: class GuardObjectNotifier
michael@0: {
michael@0:   private:
michael@0:     bool* statementDone;
michael@0: 
michael@0:   public:
michael@0:     GuardObjectNotifier() : statementDone(nullptr) { }
michael@0: 
michael@0:     ~GuardObjectNotifier() {
michael@0:       *statementDone = true;
michael@0:     }
michael@0: 
michael@0:     void setStatementDone(bool* statementIsDone) {
michael@0:       statementDone = statementIsDone;
michael@0:     }
michael@0: };
michael@0: 
michael@0: class GuardObjectNotificationReceiver
michael@0: {
michael@0:   private:
michael@0:     bool statementDone;
michael@0: 
michael@0:   public:
michael@0:     GuardObjectNotificationReceiver() : statementDone(false) { }
michael@0: 
michael@0:     ~GuardObjectNotificationReceiver() {
michael@0:       /*
michael@0:        * Assert that the guard object was not used as a temporary.  (Note that
michael@0:        * this assert might also fire if init is not called because the guard
michael@0:        * object's implementation is not using the above macros correctly.)
michael@0:        */
michael@0:       MOZ_ASSERT(statementDone);
michael@0:     }
michael@0: 
michael@0:     void init(const GuardObjectNotifier& constNotifier) {
michael@0:       /*
michael@0:        * constNotifier is passed as a const reference so that we can pass a
michael@0:        * temporary, but we really intend it as non-const.
michael@0:        */
michael@0:       GuardObjectNotifier& notifier = const_cast<GuardObjectNotifier&>(constNotifier);
michael@0:       notifier.setStatementDone(&statementDone);
michael@0:     }
michael@0: };
michael@0: 
michael@0: } /* namespace detail */
michael@0: } /* namespace mozilla */
michael@0: 
michael@0: #endif /* DEBUG */
michael@0: 
michael@0: #ifdef DEBUG
michael@0: #  define MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER \
michael@0:      mozilla::detail::GuardObjectNotificationReceiver _mCheckNotUsedAsTemporary;
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM \
michael@0:      , const mozilla::detail::GuardObjectNotifier& _notifier = \
michael@0:          mozilla::detail::GuardObjectNotifier()
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM \
michael@0:      const mozilla::detail::GuardObjectNotifier& _notifier = \
michael@0:          mozilla::detail::GuardObjectNotifier()
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL \
michael@0:      , const mozilla::detail::GuardObjectNotifier& _notifier
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL \
michael@0:      const mozilla::detail::GuardObjectNotifier& _notifier
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT \
michael@0:      , _notifier
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT \
michael@0:        _notifier
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_INIT \
michael@0:      do { _mCheckNotUsedAsTemporary.init(_notifier); } while (0)
michael@0: #else
michael@0: #  define MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT
michael@0: #  define MOZ_GUARD_OBJECT_NOTIFIER_INIT do { } while (0)
michael@0: #endif
michael@0: 
michael@0: #endif /* __cplusplus */
michael@0: 
michael@0: #endif /* mozilla_GuardObjects_h */