From 5f8de423f190bbb79a62f804151bc24824fa32d8 Mon Sep 17 00:00:00 2001 From: "Matt A. Tobin" Date: Fri, 2 Feb 2018 04:16:08 -0500 Subject: Add m-esr52 at 52.6.0 --- mfbt/GuardObjects.h | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 167 insertions(+) create mode 100644 mfbt/GuardObjects.h (limited to 'mfbt/GuardObjects.h') diff --git a/mfbt/GuardObjects.h b/mfbt/GuardObjects.h new file mode 100644 index 000000000..9440c71c4 --- /dev/null +++ b/mfbt/GuardObjects.h @@ -0,0 +1,167 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* 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/Move.h" +#include "mozilla/Types.h" + +#ifdef __cplusplus + +#ifdef DEBUG + +/** + * A custom define is used rather than |mozPoisonValue()| due to cascading + * build failures relating to how mfbt is linked on different operating + * systems. See bug 1160253. + */ +#define MOZ_POISON uintptr_t(-1) + +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 GuardObjectNotifier +{ +private: + bool* mStatementDone; + +public: + GuardObjectNotifier() + : mStatementDone(reinterpret_cast(MOZ_POISON)) + { + } + + ~GuardObjectNotifier() + { + // Assert that the GuardObjectNotifier has been properly initialized by + // using the |MOZ_GUARD_OBJECT_NOTIFIER_INIT| macro. A poison value is + // used rather than a null check to appease static analyzers that were + // (incorrectly) detecting null pointer dereferences. + MOZ_ASSERT(mStatementDone != reinterpret_cast(MOZ_POISON)); + *mStatementDone = true; + } + + void setStatementDone(bool* aStatementIsDone) + { + mStatementDone = aStatementIsDone; + } +}; + +class GuardObjectNotificationReceiver +{ +private: + bool mStatementDone; + +public: + GuardObjectNotificationReceiver() : mStatementDone(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(mStatementDone); + } + + void init(GuardObjectNotifier& aNotifier) + { + aNotifier.setStatementDone(&mStatementDone); + } +}; + +} /* namespace detail */ +} /* namespace mozilla */ + +#undef MOZ_POISON + +#endif /* DEBUG */ + +#ifdef DEBUG +# define MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER \ + mozilla::detail::GuardObjectNotificationReceiver _mCheckNotUsedAsTemporary; +# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM \ + , mozilla::detail::GuardObjectNotifier&& _notifier = \ + mozilla::detail::GuardObjectNotifier() +# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM \ + mozilla::detail::GuardObjectNotifier&& _notifier = \ + mozilla::detail::GuardObjectNotifier() +# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_IN_IMPL \ + , mozilla::detail::GuardObjectNotifier&& _notifier +# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL \ + mozilla::detail::GuardObjectNotifier&& _notifier +# define MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT \ + , mozilla::Move(_notifier) +# define MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_TO_PARENT \ + mozilla::Move(_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_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 */ -- cgit v1.2.3