/* -*- 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/. */ /* CRTP refcounting templates. Do not use unless you are an Expert. */ #ifndef mozilla_RefCounted_h #define mozilla_RefCounted_h #include "mozilla/AlreadyAddRefed.h" #include "mozilla/Assertions.h" #include "mozilla/Atomics.h" #include "mozilla/Attributes.h" #include "mozilla/Move.h" #include "mozilla/RefCountType.h" #include "mozilla/TypeTraits.h" #if defined(MOZILLA_INTERNAL_API) #include "nsXPCOM.h" #endif #if defined(MOZILLA_INTERNAL_API) && \ (defined(DEBUG) || defined(FORCE_BUILD_REFCNT_LOGGING)) #define MOZ_REFCOUNTED_LEAK_CHECKING #endif namespace mozilla { /** * RefCounted<T> is a sort of a "mixin" for a class T. RefCounted * manages, well, refcounting for T, and because RefCounted is * parameterized on T, RefCounted<T> can call T's destructor directly. * This means T doesn't need to have a virtual dtor and so doesn't * need a vtable. * * RefCounted<T> is created with refcount == 0. Newly-allocated * RefCounted<T> must immediately be assigned to a RefPtr to make the * refcount > 0. It's an error to allocate and free a bare * RefCounted<T>, i.e. outside of the RefPtr machinery. Attempts to * do so will abort DEBUG builds. * * Live RefCounted<T> have refcount > 0. The lifetime (refcounts) of * live RefCounted<T> are controlled by RefPtr<T> and * RefPtr<super/subclass of T>. Upon a transition from refcounted==1 * to 0, the RefCounted<T> "dies" and is destroyed. The "destroyed" * state is represented in DEBUG builds by refcount==0xffffdead. This * state distinguishes use-before-ref (refcount==0) from * use-after-destroy (refcount==0xffffdead). * * Note that when deriving from RefCounted or AtomicRefCounted, you * should add MOZ_DECLARE_REFCOUNTED_TYPENAME(ClassName) to the public * section of your class, where ClassName is the name of your class. */ namespace detail { const MozRefCountType DEAD = 0xffffdead; // When building code that gets compiled into Gecko, try to use the // trace-refcount leak logging facilities. #ifdef MOZ_REFCOUNTED_LEAK_CHECKING class RefCountLogger { public: static void logAddRef(const void* aPointer, MozRefCountType aRefCount, const char* aTypeName, uint32_t aInstanceSize) { MOZ_ASSERT(aRefCount != DEAD); NS_LogAddRef(const_cast<void*>(aPointer), aRefCount, aTypeName, aInstanceSize); } static void logRelease(const void* aPointer, MozRefCountType aRefCount, const char* aTypeName) { MOZ_ASSERT(aRefCount != DEAD); NS_LogRelease(const_cast<void*>(aPointer), aRefCount, aTypeName); } }; #endif // This is used WeakPtr.h as well as this file. enum RefCountAtomicity { AtomicRefCount, NonAtomicRefCount }; template<typename T, RefCountAtomicity Atomicity> class RefCounted { protected: RefCounted() : mRefCnt(0) {} ~RefCounted() { MOZ_ASSERT(mRefCnt == detail::DEAD); } public: // Compatibility with nsRefPtr. void AddRef() const { // Note: this method must be thread safe for AtomicRefCounted. MOZ_ASSERT(int32_t(mRefCnt) >= 0); #ifndef MOZ_REFCOUNTED_LEAK_CHECKING ++mRefCnt; #else const char* type = static_cast<const T*>(this)->typeName(); uint32_t size = static_cast<const T*>(this)->typeSize(); const void* ptr = static_cast<const T*>(this); MozRefCountType cnt = ++mRefCnt; detail::RefCountLogger::logAddRef(ptr, cnt, type, size); #endif } void Release() const { // Note: this method must be thread safe for AtomicRefCounted. MOZ_ASSERT(int32_t(mRefCnt) > 0); #ifndef MOZ_REFCOUNTED_LEAK_CHECKING MozRefCountType cnt = --mRefCnt; #else const char* type = static_cast<const T*>(this)->typeName(); const void* ptr = static_cast<const T*>(this); MozRefCountType cnt = --mRefCnt; // Note: it's not safe to touch |this| after decrementing the refcount, // except for below. detail::RefCountLogger::logRelease(ptr, cnt, type); #endif if (0 == cnt) { // Because we have atomically decremented the refcount above, only // one thread can get a 0 count here, so as long as we can assume that // everything else in the system is accessing this object through // RefPtrs, it's safe to access |this| here. #ifdef DEBUG mRefCnt = detail::DEAD; #endif delete static_cast<const T*>(this); } } // Compatibility with wtf::RefPtr. void ref() { AddRef(); } void deref() { Release(); } MozRefCountType refCount() const { return mRefCnt; } bool hasOneRef() const { MOZ_ASSERT(mRefCnt > 0); return mRefCnt == 1; } private: mutable typename Conditional<Atomicity == AtomicRefCount, Atomic<MozRefCountType>, MozRefCountType>::Type mRefCnt; }; #ifdef MOZ_REFCOUNTED_LEAK_CHECKING // Passing override for the optional argument marks the typeName and // typeSize functions defined by this macro as overrides. #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T, ...) \ virtual const char* typeName() const __VA_ARGS__ { return #T; } \ virtual size_t typeSize() const __VA_ARGS__ { return sizeof(*this); } #else #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T, ...) #endif // Note that this macro is expanded unconditionally because it declares only // two small inline functions which will hopefully get eliminated by the linker // in non-leak-checking builds. #define MOZ_DECLARE_REFCOUNTED_TYPENAME(T) \ const char* typeName() const { return #T; } \ size_t typeSize() const { return sizeof(*this); } } // namespace detail template<typename T> class RefCounted : public detail::RefCounted<T, detail::NonAtomicRefCount> { public: ~RefCounted() { static_assert(IsBaseOf<RefCounted, T>::value, "T must derive from RefCounted<T>"); } }; namespace external { /** * AtomicRefCounted<T> is like RefCounted<T>, with an atomically updated * reference counter. * * NOTE: Please do not use this class, use NS_INLINE_DECL_THREADSAFE_REFCOUNTING * instead. */ template<typename T> class AtomicRefCounted : public mozilla::detail::RefCounted<T, mozilla::detail::AtomicRefCount> { public: ~AtomicRefCounted() { static_assert(IsBaseOf<AtomicRefCounted, T>::value, "T must derive from AtomicRefCounted<T>"); } }; } // namespace external } // namespace mozilla #endif // mozilla_RefCounted_h