mirror of
https://github.com/mozilla/gecko-dev.git
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396 lines
11 KiB
C++
396 lines
11 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* Helpers for defining and using refcounted objects. */
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#ifndef mozilla_RefPtr_h
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#define mozilla_RefPtr_h
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#include "mozilla/Assertions.h"
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#include "mozilla/Atomics.h"
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#include "mozilla/Attributes.h"
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#include "mozilla/NullPtr.h"
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#include "mozilla/RefCountType.h"
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#include "mozilla/TypeTraits.h"
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#if defined(MOZILLA_INTERNAL_API)
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#include "nsXPCOM.h"
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#endif
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#if defined(MOZILLA_INTERNAL_API) && \
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(defined(DEBUG) || defined(FORCE_BUILD_REFCNT_LOGGING))
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#define MOZ_REFCOUNTED_LEAK_CHECKING
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#endif
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namespace mozilla {
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template<typename T> class RefCounted;
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template<typename T> class RefPtr;
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template<typename T> class TemporaryRef;
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template<typename T> class OutParamRef;
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template<typename T> OutParamRef<T> byRef(RefPtr<T>&);
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/**
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* RefCounted<T> is a sort of a "mixin" for a class T. RefCounted
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* manages, well, refcounting for T, and because RefCounted is
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* parameterized on T, RefCounted<T> can call T's destructor directly.
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* This means T doesn't need to have a virtual dtor and so doesn't
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* need a vtable.
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*
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* RefCounted<T> is created with refcount == 0. Newly-allocated
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* RefCounted<T> must immediately be assigned to a RefPtr to make the
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* refcount > 0. It's an error to allocate and free a bare
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* RefCounted<T>, i.e. outside of the RefPtr machinery. Attempts to
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* do so will abort DEBUG builds.
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*
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* Live RefCounted<T> have refcount > 0. The lifetime (refcounts) of
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* live RefCounted<T> are controlled by RefPtr<T> and
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* RefPtr<super/subclass of T>. Upon a transition from refcounted==1
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* to 0, the RefCounted<T> "dies" and is destroyed. The "destroyed"
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* state is represented in DEBUG builds by refcount==0xffffdead. This
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* state distinguishes use-before-ref (refcount==0) from
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* use-after-destroy (refcount==0xffffdead).
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*
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* Note that when deriving from RefCounted or AtomicRefCounted, you
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* should add MOZ_DECLARE_REFCOUNTED_TYPENAME(ClassName) to the public
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* section of your class, where ClassName is the name of your class.
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*/
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namespace detail {
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#ifdef DEBUG
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const MozRefCountType DEAD = 0xffffdead;
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#endif
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// When building code that gets compiled into Gecko, try to use the
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// trace-refcount leak logging facilities.
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#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
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class RefCountLogger
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{
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public:
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static void logAddRef(const void* aPointer, MozRefCountType aRefCount,
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const char* aTypeName, uint32_t aInstanceSize)
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{
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MOZ_ASSERT(aRefCount != DEAD);
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NS_LogAddRef(const_cast<void*>(aPointer), aRefCount, aTypeName,
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aInstanceSize);
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}
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static void logRelease(const void* aPointer, MozRefCountType aRefCount,
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const char* aTypeName)
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{
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MOZ_ASSERT(aRefCount != DEAD);
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NS_LogRelease(const_cast<void*>(aPointer), aRefCount, aTypeName);
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}
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};
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#endif
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// This is used WeakPtr.h as well as this file.
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enum RefCountAtomicity
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{
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AtomicRefCount,
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NonAtomicRefCount
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};
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template<typename T, RefCountAtomicity Atomicity>
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class RefCounted
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{
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friend class RefPtr<T>;
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protected:
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RefCounted() : mRefCnt(0) {}
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~RefCounted() { MOZ_ASSERT(mRefCnt == detail::DEAD); }
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public:
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// Compatibility with nsRefPtr.
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void AddRef() const
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{
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// Note: this method must be thread safe for AtomicRefCounted.
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MOZ_ASSERT(int32_t(mRefCnt) >= 0);
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#ifndef MOZ_REFCOUNTED_LEAK_CHECKING
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++mRefCnt;
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#else
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const char* type = static_cast<const T*>(this)->typeName();
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uint32_t size = static_cast<const T*>(this)->typeSize();
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const void* ptr = static_cast<const T*>(this);
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MozRefCountType cnt = ++mRefCnt;
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detail::RefCountLogger::logAddRef(ptr, cnt, type, size);
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#endif
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}
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void Release() const
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{
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// Note: this method must be thread safe for AtomicRefCounted.
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MOZ_ASSERT(int32_t(mRefCnt) > 0);
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#ifndef MOZ_REFCOUNTED_LEAK_CHECKING
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MozRefCountType cnt = --mRefCnt;
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#else
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const char* type = static_cast<const T*>(this)->typeName();
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const void* ptr = static_cast<const T*>(this);
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MozRefCountType cnt = --mRefCnt;
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// Note: it's not safe to touch |this| after decrementing the refcount,
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// except for below.
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detail::RefCountLogger::logRelease(ptr, cnt, type);
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#endif
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if (0 == cnt) {
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// Because we have atomically decremented the refcount above, only
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// one thread can get a 0 count here, so as long as we can assume that
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// everything else in the system is accessing this object through
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// RefPtrs, it's safe to access |this| here.
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#ifdef DEBUG
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mRefCnt = detail::DEAD;
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#endif
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delete static_cast<const T*>(this);
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}
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}
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// Compatibility with wtf::RefPtr.
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void ref() { AddRef(); }
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void deref() { Release(); }
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MozRefCountType refCount() const { return mRefCnt; }
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bool hasOneRef() const
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{
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MOZ_ASSERT(mRefCnt > 0);
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return mRefCnt == 1;
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}
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private:
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mutable typename Conditional<Atomicity == AtomicRefCount,
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Atomic<MozRefCountType>,
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MozRefCountType>::Type mRefCnt;
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};
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#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
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#define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T) \
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virtual const char* typeName() const { return #T; } \
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virtual size_t typeSize() const { return sizeof(*this); }
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#else
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#define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T)
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#endif
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// Note that this macro is expanded unconditionally because it declares only
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// two small inline functions which will hopefully get eliminated by the linker
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// in non-leak-checking builds.
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#define MOZ_DECLARE_REFCOUNTED_TYPENAME(T) \
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const char* typeName() const { return #T; } \
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size_t typeSize() const { return sizeof(*this); }
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} // namespace detail
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template<typename T>
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class RefCounted : public detail::RefCounted<T, detail::NonAtomicRefCount>
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{
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public:
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~RefCounted()
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{
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static_assert(IsBaseOf<RefCounted, T>::value,
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"T must derive from RefCounted<T>");
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}
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};
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namespace external {
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/**
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* AtomicRefCounted<T> is like RefCounted<T>, with an atomically updated
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* reference counter.
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*
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* NOTE: Please do not use this class, use NS_INLINE_DECL_THREADSAFE_REFCOUNTING
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* instead.
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*/
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template<typename T>
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class AtomicRefCounted :
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public mozilla::detail::RefCounted<T, mozilla::detail::AtomicRefCount>
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{
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public:
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~AtomicRefCounted()
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{
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static_assert(IsBaseOf<AtomicRefCounted, T>::value,
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"T must derive from AtomicRefCounted<T>");
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}
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};
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} // namespace external
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/**
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* RefPtr points to a refcounted thing that has AddRef and Release
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* methods to increase/decrease the refcount, respectively. After a
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* RefPtr<T> is assigned a T*, the T* can be used through the RefPtr
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* as if it were a T*.
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*
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* A RefPtr can forget its underlying T*, which results in the T*
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* being wrapped in a temporary object until the T* is either
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* re-adopted from or released by the temporary.
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*/
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template<typename T>
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class RefPtr
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{
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// To allow them to use unref()
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friend class TemporaryRef<T>;
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friend class OutParamRef<T>;
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struct DontRef {};
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public:
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RefPtr() : mPtr(0) {}
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RefPtr(const RefPtr& aOther) : mPtr(ref(aOther.mPtr)) {}
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MOZ_IMPLICIT RefPtr(const TemporaryRef<T>& aOther) : mPtr(aOther.drop()) {}
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MOZ_IMPLICIT RefPtr(T* aVal) : mPtr(ref(aVal)) {}
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template<typename U>
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RefPtr(const RefPtr<U>& aOther) : mPtr(ref(aOther.get())) {}
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~RefPtr() { unref(mPtr); }
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RefPtr& operator=(const RefPtr& aOther)
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{
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assign(ref(aOther.mPtr));
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return *this;
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}
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RefPtr& operator=(const TemporaryRef<T>& aOther)
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{
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assign(aOther.drop());
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return *this;
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}
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RefPtr& operator=(T* aVal)
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{
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assign(ref(aVal));
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return *this;
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}
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template<typename U>
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RefPtr& operator=(const RefPtr<U>& aOther)
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{
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assign(ref(aOther.get()));
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return *this;
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}
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TemporaryRef<T> forget()
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{
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T* tmp = mPtr;
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mPtr = nullptr;
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return TemporaryRef<T>(tmp, DontRef());
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}
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T* get() const { return mPtr; }
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operator T*() const { return mPtr; }
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T* operator->() const { return mPtr; }
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T& operator*() const { return *mPtr; }
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template<typename U>
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operator TemporaryRef<U>() { return TemporaryRef<U>(mPtr); }
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private:
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void assign(T* aVal)
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{
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unref(mPtr);
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mPtr = aVal;
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}
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T* mPtr;
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static MOZ_ALWAYS_INLINE T* ref(T* aVal)
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{
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if (aVal) {
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aVal->AddRef();
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}
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return aVal;
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}
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static MOZ_ALWAYS_INLINE void unref(T* aVal)
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{
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if (aVal) {
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aVal->Release();
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}
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}
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};
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/**
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* TemporaryRef<T> represents an object that holds a temporary
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* reference to a T. TemporaryRef objects can't be manually ref'd or
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* unref'd (being temporaries, not lvalues), so can only relinquish
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* references to other objects, or unref on destruction.
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*/
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template<typename T>
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class TemporaryRef
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{
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// To allow it to construct TemporaryRef from a bare T*
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friend class RefPtr<T>;
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typedef typename RefPtr<T>::DontRef DontRef;
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public:
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MOZ_IMPLICIT TemporaryRef(T* aVal) : mPtr(RefPtr<T>::ref(aVal)) {}
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TemporaryRef(const TemporaryRef& aOther) : mPtr(aOther.drop()) {}
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template<typename U>
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TemporaryRef(const TemporaryRef<U>& aOther) : mPtr(aOther.drop()) {}
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~TemporaryRef() { RefPtr<T>::unref(mPtr); }
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T* drop() const
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{
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T* tmp = mPtr;
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mPtr = nullptr;
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return tmp;
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}
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private:
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TemporaryRef(T* aVal, const DontRef&) : mPtr(aVal) {}
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mutable T* mPtr;
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TemporaryRef() MOZ_DELETE;
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void operator=(const TemporaryRef&) MOZ_DELETE;
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};
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/**
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* OutParamRef is a wrapper that tracks a refcounted pointer passed as
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* an outparam argument to a function. OutParamRef implements COM T**
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* outparam semantics: this requires the callee to AddRef() the T*
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* returned through the T** outparam on behalf of the caller. This
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* means the caller (through OutParamRef) must Release() the old
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* object contained in the tracked RefPtr. It's OK if the callee
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* returns the same T* passed to it through the T** outparam, as long
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* as the callee obeys the COM discipline.
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*
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* Prefer returning TemporaryRef<T> from functions over creating T**
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* outparams and passing OutParamRef<T> to T**. Prefer RefPtr<T>*
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* outparams over T** outparams.
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*/
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template<typename T>
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class OutParamRef
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{
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friend OutParamRef byRef<T>(RefPtr<T>&);
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public:
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~OutParamRef()
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{
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RefPtr<T>::unref(mRefPtr.mPtr);
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mRefPtr.mPtr = mTmp;
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}
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operator T**() { return &mTmp; }
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private:
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explicit OutParamRef(RefPtr<T>& p) : mRefPtr(p), mTmp(p.get()) {}
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RefPtr<T>& mRefPtr;
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T* mTmp;
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OutParamRef() MOZ_DELETE;
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OutParamRef& operator=(const OutParamRef&) MOZ_DELETE;
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};
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/**
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* byRef cooperates with OutParamRef to implement COM outparam semantics.
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*/
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template<typename T>
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OutParamRef<T>
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byRef(RefPtr<T>& aPtr)
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{
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return OutParamRef<T>(aPtr);
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}
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} // namespace mozilla
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#endif /* mozilla_RefPtr_h */
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