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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_MEMORY_REF_COUNTED_H_
#define BASE_MEMORY_REF_COUNTED_H_
#include <stddef.h>
#include <utility>
#include "base/atomic_ref_count.h"
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/gtest_prod_util.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/scoped_refptr.h"
#include "base/sequence_checker.h"
#include "base/threading/thread_collision_warner.h"
#include "build/build_config.h"
namespace base {
namespace subtle {
class BASE_EXPORT RefCountedBase {
public:
bool HasOneRef() const { return ref_count_ == 1; }
bool HasAtLeastOneRef() const { return ref_count_ >= 1; }
protected:
explicit RefCountedBase(StartRefCountFromZeroTag) {
#if DCHECK_IS_ON()
sequence_checker_.DetachFromSequence();
#endif
}
explicit RefCountedBase(StartRefCountFromOneTag) : ref_count_(1) {
#if DCHECK_IS_ON()
needs_adopt_ref_ = true;
sequence_checker_.DetachFromSequence();
#endif
}
~RefCountedBase() {
#if DCHECK_IS_ON()
DCHECK(in_dtor_) << "RefCounted object deleted without calling Release()";
#endif
}
void AddRef() const {
// TODO(maruel): Add back once it doesn't assert 500 times/sec.
// Current thread books the critical section "AddRelease"
// without release it.
// DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#if DCHECK_IS_ON()
DCHECK(!in_dtor_);
DCHECK(!needs_adopt_ref_)
<< "This RefCounted object is created with non-zero reference count."
<< " The first reference to such a object has to be made by AdoptRef or"
<< " MakeRefCounted.";
if (ref_count_ >= 1) {
DCHECK(CalledOnValidSequence());
}
#endif
AddRefImpl();
}
// Returns true if the object should self-delete.
bool Release() const {
--ref_count_;
// TODO(maruel): Add back once it doesn't assert 500 times/sec.
// Current thread books the critical section "AddRelease"
// without release it.
// DFAKE_SCOPED_LOCK_THREAD_LOCKED(add_release_);
#if DCHECK_IS_ON()
DCHECK(!in_dtor_);
if (ref_count_ == 0)
in_dtor_ = true;
if (ref_count_ >= 1)
DCHECK(CalledOnValidSequence());
if (ref_count_ == 1)
sequence_checker_.DetachFromSequence();
#endif
return ref_count_ == 0;
}
// Returns true if it is safe to read or write the object, from a thread
// safety standpoint. Should be DCHECK'd from the methods of RefCounted
// classes if there is a danger of objects being shared across threads.
//
// This produces fewer false positives than adding a separate SequenceChecker
// into the subclass, because it automatically detaches from the sequence when
// the reference count is 1 (and never fails if there is only one reference).
//
// This means unlike a separate SequenceChecker, it will permit a singly
// referenced object to be passed between threads (not holding a reference on
// the sending thread), but will trap if the sending thread holds onto a
// reference, or if the object is accessed from multiple threads
// simultaneously.
bool IsOnValidSequence() const {
#if DCHECK_IS_ON()
return ref_count_ <= 1 || CalledOnValidSequence();
#else
return true;
#endif
}
private:
template <typename U>
friend scoped_refptr<U> base::AdoptRef(U*);
FRIEND_TEST_ALL_PREFIXES(RefCountedDeathTest, TestOverflowCheck);
void Adopted() const {
#if DCHECK_IS_ON()
DCHECK(needs_adopt_ref_);
needs_adopt_ref_ = false;
#endif
}
#if defined(ARCH_CPU_64_BITS)
void AddRefImpl() const;
#else
void AddRefImpl() const { ++ref_count_; }
#endif
#if DCHECK_IS_ON()
bool CalledOnValidSequence() const;
#endif
mutable uint32_t ref_count_ = 0;
#if DCHECK_IS_ON()
mutable bool needs_adopt_ref_ = false;
mutable bool in_dtor_ = false;
mutable SequenceChecker sequence_checker_;
#endif
DFAKE_MUTEX(add_release_);
DISALLOW_COPY_AND_ASSIGN(RefCountedBase);
};
class BASE_EXPORT RefCountedThreadSafeBase {
public:
bool HasOneRef() const;
bool HasAtLeastOneRef() const;
protected:
explicit constexpr RefCountedThreadSafeBase(StartRefCountFromZeroTag) {}
explicit constexpr RefCountedThreadSafeBase(StartRefCountFromOneTag)
: ref_count_(1) {
#if DCHECK_IS_ON()
needs_adopt_ref_ = true;
#endif
}
#if DCHECK_IS_ON()
~RefCountedThreadSafeBase();
#else
~RefCountedThreadSafeBase() = default;
#endif
// Release and AddRef are suitable for inlining on X86 because they generate
// very small code sequences. On other platforms (ARM), it causes a size
// regression and is probably not worth it.
#if defined(ARCH_CPU_X86_FAMILY)
// Returns true if the object should self-delete.
bool Release() const { return ReleaseImpl(); }
void AddRef() const { AddRefImpl(); }
void AddRefWithCheck() const { AddRefWithCheckImpl(); }
#else
// Returns true if the object should self-delete.
bool Release() const;
void AddRef() const;
void AddRefWithCheck() const;
#endif
private:
template <typename U>
friend scoped_refptr<U> base::AdoptRef(U*);
void Adopted() const {
#if DCHECK_IS_ON()
DCHECK(needs_adopt_ref_);
needs_adopt_ref_ = false;
#endif
}
ALWAYS_INLINE void AddRefImpl() const {
#if DCHECK_IS_ON()
DCHECK(!in_dtor_);
DCHECK(!needs_adopt_ref_)
<< "This RefCounted object is created with non-zero reference count."
<< " The first reference to such a object has to be made by AdoptRef or"
<< " MakeRefCounted.";
#endif
ref_count_.Increment();
}
ALWAYS_INLINE void AddRefWithCheckImpl() const {
#if DCHECK_IS_ON()
DCHECK(!in_dtor_);
DCHECK(!needs_adopt_ref_)
<< "This RefCounted object is created with non-zero reference count."
<< " The first reference to such a object has to be made by AdoptRef or"
<< " MakeRefCounted.";
#endif
CHECK(ref_count_.Increment() > 0);
}
ALWAYS_INLINE bool ReleaseImpl() const {
#if DCHECK_IS_ON()
DCHECK(!in_dtor_);
DCHECK(!ref_count_.IsZero());
#endif
if (!ref_count_.Decrement()) {
#if DCHECK_IS_ON()
in_dtor_ = true;
#endif
return true;
}
return false;
}
mutable AtomicRefCount ref_count_{0};
#if DCHECK_IS_ON()
mutable bool needs_adopt_ref_ = false;
mutable bool in_dtor_ = false;
#endif
DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
};
} // namespace subtle
// ScopedAllowCrossThreadRefCountAccess disables the check documented on
// RefCounted below for rare pre-existing use cases where thread-safety was
// guaranteed through other means (e.g. explicit sequencing of calls across
// execution sequences when bouncing between threads in order). New callers
// should refrain from using this (callsites handling thread-safety through
// locks should use RefCountedThreadSafe per the overhead of its atomics being
// negligible compared to locks anyways and callsites doing explicit sequencing
// should properly std::move() the ref to avoid hitting this check).
// TODO(tzik): Cleanup existing use cases and remove
// ScopedAllowCrossThreadRefCountAccess.
class BASE_EXPORT ScopedAllowCrossThreadRefCountAccess final {
public:
#if DCHECK_IS_ON()
ScopedAllowCrossThreadRefCountAccess();
~ScopedAllowCrossThreadRefCountAccess();
#else
ScopedAllowCrossThreadRefCountAccess() {}
~ScopedAllowCrossThreadRefCountAccess() {}
#endif
};
//
// A base class for reference counted classes. Otherwise, known as a cheap
// knock-off of WebKit's RefCounted<T> class. To use this, just extend your
// class from it like so:
//
// class MyFoo : public base::RefCounted<MyFoo> {
// ...
// private:
// friend class base::RefCounted<MyFoo>;
// ~MyFoo();
// };
//
// You should always make your destructor non-public, to avoid any code deleting
// the object accidently while there are references to it.
//
//
// The ref count manipulation to RefCounted is NOT thread safe and has DCHECKs
// to trap unsafe cross thread usage. A subclass instance of RefCounted can be
// passed to another execution sequence only when its ref count is 1. If the ref
// count is more than 1, the RefCounted class verifies the ref updates are made
// on the same execution sequence as the previous ones. The subclass can also
// manually call IsOnValidSequence to trap other non-thread-safe accesses; see
// the documentation for that method.
//
//
// The reference count starts from zero by default, and we intended to migrate
// to start-from-one ref count. Put REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE() to
// the ref counted class to opt-in.
//
// If an object has start-from-one ref count, the first scoped_refptr need to be
// created by base::AdoptRef() or base::MakeRefCounted(). We can use
// base::MakeRefCounted() to create create both type of ref counted object.
//
// The motivations to use start-from-one ref count are:
// - Start-from-one ref count doesn't need the ref count increment for the
// first reference.
// - It can detect an invalid object acquisition for a being-deleted object
// that has zero ref count. That tends to happen on custom deleter that
// delays the deletion.
// TODO(tzik): Implement invalid acquisition detection.
// - Behavior parity to Blink's WTF::RefCounted, whose count starts from one.
// And start-from-one ref count is a step to merge WTF::RefCounted into
// base::RefCounted.
//
#define REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE() \
static constexpr ::base::subtle::StartRefCountFromOneTag \
kRefCountPreference = ::base::subtle::kStartRefCountFromOneTag
template <class T, typename Traits>
class RefCounted;
template <typename T>
struct DefaultRefCountedTraits {
static void Destruct(const T* x) {
RefCounted<T, DefaultRefCountedTraits>::DeleteInternal(x);
}
};
template <class T, typename Traits = DefaultRefCountedTraits<T>>
class RefCounted : public subtle::RefCountedBase {
public:
static constexpr subtle::StartRefCountFromZeroTag kRefCountPreference =
subtle::kStartRefCountFromZeroTag;
RefCounted() : subtle::RefCountedBase(T::kRefCountPreference) {}
void AddRef() const {
subtle::RefCountedBase::AddRef();
}
void Release() const {
if (subtle::RefCountedBase::Release()) {
// Prune the code paths which the static analyzer may take to simulate
// object destruction. Use-after-free errors aren't possible given the
// lifetime guarantees of the refcounting system.
ANALYZER_SKIP_THIS_PATH();
Traits::Destruct(static_cast<const T*>(this));
}
}
protected:
~RefCounted() = default;
private:
friend struct DefaultRefCountedTraits<T>;
template <typename U>
static void DeleteInternal(const U* x) {
delete x;
}
DISALLOW_COPY_AND_ASSIGN(RefCounted);
};
// Forward declaration.
template <class T, typename Traits> class RefCountedThreadSafe;
// Default traits for RefCountedThreadSafe<T>. Deletes the object when its ref
// count reaches 0. Overload to delete it on a different thread etc.
template<typename T>
struct DefaultRefCountedThreadSafeTraits {
static void Destruct(const T* x) {
// Delete through RefCountedThreadSafe to make child classes only need to be
// friend with RefCountedThreadSafe instead of this struct, which is an
// implementation detail.
RefCountedThreadSafe<T,
DefaultRefCountedThreadSafeTraits>::DeleteInternal(x);
}
};
//
// A thread-safe variant of RefCounted<T>
//
// class MyFoo : public base::RefCountedThreadSafe<MyFoo> {
// ...
// };
//
// If you're using the default trait, then you should add compile time
// asserts that no one else is deleting your object. i.e.
// private:
// friend class base::RefCountedThreadSafe<MyFoo>;
// ~MyFoo();
//
// We can use REQUIRE_ADOPTION_FOR_REFCOUNTED_TYPE() with RefCountedThreadSafe
// too. See the comment above the RefCounted definition for details.
template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T> >
class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
public:
static constexpr subtle::StartRefCountFromZeroTag kRefCountPreference =
subtle::kStartRefCountFromZeroTag;
explicit RefCountedThreadSafe()
: subtle::RefCountedThreadSafeBase(T::kRefCountPreference) {}
void AddRef() const { AddRefImpl(T::kRefCountPreference); }
void Release() const {
if (subtle::RefCountedThreadSafeBase::Release()) {
ANALYZER_SKIP_THIS_PATH();
Traits::Destruct(static_cast<const T*>(this));
}
}
protected:
~RefCountedThreadSafe() = default;
private:
friend struct DefaultRefCountedThreadSafeTraits<T>;
template <typename U>
static void DeleteInternal(const U* x) {
delete x;
}
void AddRefImpl(subtle::StartRefCountFromZeroTag) const {
subtle::RefCountedThreadSafeBase::AddRef();
}
void AddRefImpl(subtle::StartRefCountFromOneTag) const {
subtle::RefCountedThreadSafeBase::AddRefWithCheck();
}
DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
};
//
// A thread-safe wrapper for some piece of data so we can place other
// things in scoped_refptrs<>.
//
template<typename T>
class RefCountedData
: public base::RefCountedThreadSafe< base::RefCountedData<T> > {
public:
RefCountedData() : data() {}
RefCountedData(const T& in_value) : data(in_value) {}
RefCountedData(T&& in_value) : data(std::move(in_value)) {}
T data;
private:
friend class base::RefCountedThreadSafe<base::RefCountedData<T> >;
~RefCountedData() = default;
};
template <typename T>
bool operator==(const RefCountedData<T>& lhs, const RefCountedData<T>& rhs) {
return lhs.data == rhs.data;
}
template <typename T>
bool operator!=(const RefCountedData<T>& lhs, const RefCountedData<T>& rhs) {
return !(lhs == rhs);
}
} // namespace base
#endif // BASE_MEMORY_REF_COUNTED_H_