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194 lines
7.3 KiB
C++
194 lines
7.3 KiB
C++
/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is nsAutoRestore.h.
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*
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* The Initial Developer of the Original Code is the Mozilla Foundation.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* L. David Baron <dbaron@dbaron.org>, Mozilla Corporation (original author)
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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/* functions for restoring saved values at the end of a C++ scope */
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#ifndef mozilla_AutoRestore_h_
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#define mozilla_AutoRestore_h_
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#include "prtypes.h"
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#include "nsDebug.h"
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namespace mozilla {
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/**
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* The following classes are designed to cause assertions to detect
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* inadvertent use of guard objects as temporaries. In other words,
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* when we have a guard object whose only purpose is its constructor and
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* destructor (and is never otherwise referenced), the intended use
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* might be:
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* AutoRestore savePainting(mIsPainting);
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* but is is easy to accidentally write:
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* AutoRestore(mIsPainting);
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* which compiles just fine, but runs the destructor well before the
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* intended time.
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*
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* They work by adding (#ifdef DEBUG) an additional parameter to the
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* guard object's constructor, with a default value, so that users of
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* the guard object's API do not need to do anything. The default value
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* of this parameter is a temporary object. C++ (ISO/IEC 14882:1998),
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* section 12.2 [class.temporary], clauses 4 and 5 seem to assume a
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* guarantee that temporaries are destroyed in the reverse of their
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* construction order, but I actually can't find a statement that that
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* is true in the general case (beyond the two specific cases mentioned
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* there). However, it seems to be true.
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*
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* These classes are intended to be used only via the macros immediately
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* below them:
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* MOZILLA_DECL_USE_GUARD_OBJECT_NOTIFIER declares (ifdef DEBUG) a member
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* variable, and should be put where a declaration of a private
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* member variable would be placed.
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* MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM should be placed at the end of the
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* parameters to each constructor of the guard object; it declares
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* (ifdef DEBUG) an additional parameter. (But use the *_ONLY_PARAM
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* variant for constructors that take no other parameters.)
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* MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL should likewise be used in
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* the implementation of such constructors when they are not inline.
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* MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT should be used in
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* the implementation of such constructors to pass the parameter to
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* a base class that also uses these macros
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* MOZILLA_GUARD_OBJECT_NOTIFIER_INIT is a statement that belongs in each
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* constructor. It uses the parameter declared by
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* MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM.
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*
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* For more details, and examples of using these macros, see
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* https://developer.mozilla.org/en/Using_RAII_classes_in_Mozilla
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*/
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#ifdef DEBUG
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class GuardObjectNotifier
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{
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private:
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bool* mStatementDone;
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public:
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GuardObjectNotifier() : mStatementDone(NULL) {}
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~GuardObjectNotifier() {
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*mStatementDone = true;
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}
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void SetStatementDone(bool *aStatementDone) {
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mStatementDone = aStatementDone;
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}
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};
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class GuardObjectNotificationReceiver
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{
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private:
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bool mStatementDone;
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public:
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GuardObjectNotificationReceiver() : mStatementDone(false) {}
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~GuardObjectNotificationReceiver() {
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/*
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* Assert that the guard object was not used as a temporary.
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* (Note that this assert might also fire if Init is not called
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* because the guard object's implementation is not using the
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* above macros correctly.)
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*/
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NS_ABORT_IF_FALSE(mStatementDone,
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"guard object used as temporary");
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}
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void Init(const GuardObjectNotifier &aNotifier) {
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/*
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* aNotifier is passed as a const reference so that we can pass a
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* temporary, but we really intend it as non-const
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*/
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const_cast<GuardObjectNotifier&>(aNotifier).
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SetStatementDone(&mStatementDone);
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}
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};
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#define MOZILLA_DECL_USE_GUARD_OBJECT_NOTIFIER \
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mozilla::GuardObjectNotificationReceiver _mCheckNotUsedAsTemporary;
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM \
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, const mozilla::GuardObjectNotifier& _notifier = \
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mozilla::GuardObjectNotifier()
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_ONLY_PARAM \
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const mozilla::GuardObjectNotifier& _notifier = \
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mozilla::GuardObjectNotifier()
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL \
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, const mozilla::GuardObjectNotifier& _notifier
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT \
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, _notifier
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_INIT \
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PR_BEGIN_MACRO _mCheckNotUsedAsTemporary.Init(_notifier); PR_END_MACRO
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#else /* defined(DEBUG) */
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#define MOZILLA_DECL_USE_GUARD_OBJECT_NOTIFIER
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_ONLY_PARAM
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT
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#define MOZILLA_GUARD_OBJECT_NOTIFIER_INIT PR_BEGIN_MACRO PR_END_MACRO
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#endif /* !defined(DEBUG) */
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/**
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* Save the current value of a variable and restore it when the object
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* goes out of scope. For example:
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* {
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* AutoRestore<PRBool> savePainting(mIsPainting);
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* mIsPainting = PR_TRUE;
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*
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* // ... your code here ...
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*
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* // mIsPainting is reset to its old value at the end of this block
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* }
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*/
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template <class T>
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class NS_STACK_CLASS AutoRestore
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{
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private:
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T& mLocation;
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T mValue;
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MOZILLA_DECL_USE_GUARD_OBJECT_NOTIFIER
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public:
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AutoRestore(T& aValue MOZILLA_GUARD_OBJECT_NOTIFIER_PARAM)
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: mLocation(aValue), mValue(aValue)
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{
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MOZILLA_GUARD_OBJECT_NOTIFIER_INIT;
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}
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~AutoRestore() { mLocation = mValue; }
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};
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}
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#endif /* !defined(mozilla_AutoRestore_h_) */
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