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/* -*- 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 */
// This header provides virtual, non-templated alternatives to MFBT's
// RefCounted<T>. It intentionally uses MFBT coding style with the intention of
// moving there should there be other use cases for it.
#include <type_traits>
#include "mozilla/RefPtr.h"
#include "mozilla/RefCounted.h"
namespace mozilla {
* Common base class for GenericRefCounted and GenericAtomicRefCounted.
* Having this shared base class, common to both the atomic and non-atomic
* cases, allows to have RefPtr's that don't care about whether the
* objects they're managing have atomic refcounts or not.
class GenericRefCountedBase {
virtual ~GenericRefCountedBase() = default;
// AddRef() and Release() method names are for compatibility with nsRefPtr.
virtual void AddRef() = 0;
virtual void Release() = 0;
// ref() and deref() method names are for compatibility with wtf::RefPtr.
// No virtual keywords here: if a subclass wants to override the refcounting
// mechanism, it is welcome to do so by overriding AddRef() and Release().
void ref() { AddRef(); }
void deref() { Release(); }
virtual const char* typeName() const = 0;
virtual size_t typeSize() const = 0;
namespace detail {
template <RefCountAtomicity Atomicity>
class GenericRefCounted : public GenericRefCountedBase {
GenericRefCounted() : refCnt(0) {}
virtual ~GenericRefCounted() { MOZ_ASSERT(refCnt == detail::DEAD); }
virtual void AddRef() override {
// Note: this method must be thread safe for GenericAtomicRefCounted.
MOZ_ASSERT(int32_t(refCnt) >= 0);
const char* type = typeName();
uint32_t size = typeSize();
const void* ptr = this;
MozRefCountType cnt = ++refCnt;
detail::RefCountLogger::logAddRef(ptr, cnt, type, size);
virtual void Release() override {
// Note: this method must be thread safe for GenericAtomicRefCounted.
MOZ_ASSERT(int32_t(refCnt) > 0);
MozRefCountType cnt = --refCnt;
const char* type = typeName();
const void* ptr = this;
MozRefCountType cnt = --refCnt;
// Note: it's not safe to touch |this| after decrementing the refcount,
// except for below.
detail::RefCountLogger::logRelease(ptr, cnt, type);
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
refCnt = detail::DEAD;
delete this;
MozRefCountType refCount() const { return refCnt; }
bool hasOneRef() const {
MOZ_ASSERT(refCnt > 0);
return refCnt == 1;
std::conditional_t<Atomicity == AtomicRefCount, Atomic<MozRefCountType>,
} // namespace detail
* This reference-counting base class is virtual instead of
* being templated, which is useful in cases where one needs
* genericity at binary code level, but comes at the cost
* of a moderate performance and size overhead, like anything virtual.
class GenericRefCounted
: public detail::GenericRefCounted<detail::NonAtomicRefCount> {};
* GenericAtomicRefCounted is like GenericRefCounted, with an atomically updated
* reference counter.
class GenericAtomicRefCounted
: public detail::GenericRefCounted<detail::AtomicRefCount> {};
} // namespace mozilla