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/* -*- Mode: C++; tab-width: 8; 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/. */
/* 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
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