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author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2013-12-11 22:24:18 +0000 |
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committer | <> | 2014-07-24 09:30:59 +0000 |
commit | 59e2936f588aa945e8dcd6c737523c299067e9d0 (patch) | |
tree | 97e74980cc54baa19de5faa11f5a50a0121a48ea /mfbt/GuardObjects.h | |
download | mozjs24-59e2936f588aa945e8dcd6c737523c299067e9d0.tar.gz |
Imported from /home/lorry/working-area/delta_mozilla_mozjs24/mozjs-24.2.0.tar.bz2.HEADmozjs-24.2.0master
Diffstat (limited to 'mfbt/GuardObjects.h')
-rw-r--r-- | mfbt/GuardObjects.h | 150 |
1 files changed, 150 insertions, 0 deletions
diff --git a/mfbt/GuardObjects.h b/mfbt/GuardObjects.h new file mode 100644 index 0000000..6c20589 --- /dev/null +++ b/mfbt/GuardObjects.h @@ -0,0 +1,150 @@ +/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* 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/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 GuardObjectNotifier +{ + private: + bool* statementDone; + + public: + GuardObjectNotifier() : statementDone(NULL) { } + + ~GuardObjectNotifier() { + *statementDone = true; + } + + void setStatementDone(bool* statementIsDone) { + statementDone = statementIsDone; + } +}; + +class MOZ_EXPORT 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_ONLY_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_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 */ |