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RefCounted.h
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RefCounted.h
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/*
* Copyright (C) 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*
*/
#pragma once
#include <wtf/Assertions.h>
#include <wtf/FastMalloc.h>
#include <wtf/MainThread.h>
#include <wtf/Noncopyable.h>
namespace WTF {
#if ASSERT_ENABLED || ENABLE(SECURITY_ASSERTIONS)
#define CHECK_REF_COUNTED_LIFECYCLE 1
#else
#define CHECK_REF_COUNTED_LIFECYCLE 0
#endif
// This base class holds the non-template methods and attributes.
// The RefCounted class inherits from it reducing the template bloat
// generated by the compiler (technique called template hoisting).
class RefCountedBase {
public:
// Doesn't check if m_deletionHasBegun.
void refAllowingPartiallyDestroyed() const
{
applyRefDerefThreadingCheck();
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT_WITH_SECURITY_IMPLICATION(!deletionHasEnded());
ASSERT(!m_adoptionIsRequired);
#endif
++m_refCount;
}
void ref() const
{
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
#endif
refAllowingPartiallyDestroyed();
}
bool hasOneRef() const
{
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT(!m_deletionHasBegun);
#endif
return m_refCount == 1;
}
unsigned refCount() const
{
return m_refCount;
}
void relaxAdoptionRequirement()
{
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
ASSERT(m_adoptionIsRequired);
m_adoptionIsRequired = false;
#endif
}
// Please only call this method if you really know that what you're doing is safe (e.g.
// locking at call sites).
void disableThreadingChecks()
{
#if ASSERT_ENABLED
m_areThreadingChecksEnabled = false;
#endif
}
static void enableThreadingChecksGlobally()
{
#if ASSERT_ENABLED
areThreadingChecksEnabledGlobally = true;
#endif
}
protected:
RefCountedBase()
: m_refCount(1)
#if ASSERT_ENABLED
, m_isOwnedByMainThread(isMainThread())
#endif
{
}
void applyRefDerefThreadingCheck() const
{
#if ASSERT_ENABLED
if (m_refCount == 1) {
// Likely an ownership transfer across threads that may be safe.
m_isOwnedByMainThread = isMainThread();
} else if (areThreadingChecksEnabledGlobally && m_areThreadingChecksEnabled) {
// If you hit this assertion, it means that the RefCounted object was ref/deref'd
// from both the main thread and another in a way that is likely concurrent and unsafe.
// Derive from ThreadSafeRefCounted and make sure the destructor is safe on threads
// that call deref, or ref/deref from a single thread.
ASSERT_WITH_MESSAGE(m_isOwnedByMainThread == isMainThread(), "Unsafe to ref/deref from different threads");
}
#endif
}
~RefCountedBase();
// Returns whether the pointer should be freed or not.
// Doesn't check if m_deletionHasBegun.
bool derefAllowingPartiallyDestroyedBase() const
{
applyRefDerefThreadingCheck();
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT_WITH_SECURITY_IMPLICATION(!deletionHasEnded());
ASSERT(!m_adoptionIsRequired);
#endif
ASSERT(m_refCount);
unsigned tempRefCount = m_refCount - 1;
if (!tempRefCount) {
#if CHECK_REF_COUNTED_LIFECYCLE
m_deletionHasBegun = true;
#endif
return true;
}
m_refCount = tempRefCount;
return false;
}
// Returns whether the pointer should be freed or not.
bool derefBase() const
{
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
#endif
return derefAllowingPartiallyDestroyedBase();
}
#if CHECK_REF_COUNTED_LIFECYCLE
bool deletionHasBegun() const
{
return m_deletionHasBegun;
}
bool deletionHasEnded() const;
#endif
private:
#if CHECK_REF_COUNTED_LIFECYCLE
friend void adopted(RefCountedBase*);
#endif
mutable unsigned m_refCount;
#if ASSERT_ENABLED
mutable bool m_isOwnedByMainThread;
bool m_areThreadingChecksEnabled { true };
#endif
WTF_EXPORT_PRIVATE static bool areThreadingChecksEnabledGlobally;
#if CHECK_REF_COUNTED_LIFECYCLE
mutable bool m_deletionHasBegun { false };
enum class IsAllocatedMemory : unsigned {
Scribble = 0, // Do not check for this value, it is not guaranteed to exist.
Yes = 0xFEEDB0BA,
};
mutable IsAllocatedMemory m_isAllocatedMemory { IsAllocatedMemory::Yes };
mutable bool m_adoptionIsRequired { true };
#endif
};
#if CHECK_REF_COUNTED_LIFECYCLE
inline void adopted(RefCountedBase* object)
{
if (!object)
return;
ASSERT_WITH_SECURITY_IMPLICATION(!object->m_deletionHasBegun);
object->m_adoptionIsRequired = false;
}
inline bool RefCountedBase::deletionHasEnded() const
{
return m_isAllocatedMemory != IsAllocatedMemory::Yes;
}
#endif
inline RefCountedBase::~RefCountedBase()
{
#if CHECK_REF_COUNTED_LIFECYCLE
ASSERT(m_deletionHasBegun);
ASSERT(!m_adoptionIsRequired);
m_isAllocatedMemory = IsAllocatedMemory::Scribble;
#endif
}
template<typename T, typename Deleter = std::default_delete<T>> class RefCounted : public RefCountedBase {
WTF_MAKE_NONCOPYABLE(RefCounted); WTF_MAKE_FAST_ALLOCATED;
public:
void deref() const
{
if (derefBase())
Deleter()(const_cast<T*>(static_cast<const T*>(this)));
}
void derefAllowingPartiallyDestroyed() const
{
if (derefAllowingPartiallyDestroyedBase())
Deleter()(const_cast<T*>(static_cast<const T*>(this)));
}
protected:
RefCounted() { }
~RefCounted()
{
}
};
} // namespace WTF
using WTF::RefCounted;