flutter_flutter/sky/engine/wtf/RefCounted.h

/*
 * Copyright (C) 2006, 2007, 2008, 2009, 2010 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.
 *
 */

#ifndef SKY_ENGINE_WTF_REFCOUNTED_H_
#define SKY_ENGINE_WTF_REFCOUNTED_H_

#include "flutter/sky/engine/wtf/Assertions.h"
#include "flutter/sky/engine/wtf/FastAllocBase.h"
#include "flutter/sky/engine/wtf/InstanceCounter.h"
#include "flutter/sky/engine/wtf/Noncopyable.h"
#include "flutter/sky/engine/wtf/WTFExport.h"

#if ENABLE(ASSERT)
#define CHECK_REF_COUNTED_LIFECYCLE 1
#include "flutter/sky/engine/wtf/ThreadRestrictionVerifier.h"
#else
#define CHECK_REF_COUNTED_LIFECYCLE 0
#endif

namespace WTF {

// 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 WTF_EXPORT RefCountedBase {
 public:
  void ref() {
#if CHECK_REF_COUNTED_LIFECYCLE
    // Start thread verification as soon as the ref count gets to 2. This
    // heuristic reflects the fact that items are often created on one thread
    // and then given to another thread to be used.
    // FIXME: Make this restriction tigher. Especially as we move to more
    // common methods for sharing items across threads like CrossThreadCopier.h
    // We should be able to add a "detachFromThread" method to make this
    // explicit.
    if (m_refCount == 1)
      m_verifier.setShared(true);
    // If this assert fires, it either indicates a thread safety issue or
    // that the verification needs to change. See ThreadRestrictionVerifier for
    // the different modes.
    ASSERT(m_verifier.isSafeToUse());
    ASSERT(!m_adoptionIsRequired);
#endif
    ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
    ++m_refCount;
  }

  bool hasOneRef() const {
    ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
#if CHECK_REF_COUNTED_LIFECYCLE
    ASSERT(m_verifier.isSafeToUse());
#endif
    return m_refCount == 1;
  }

  int refCount() const {
#if CHECK_REF_COUNTED_LIFECYCLE
    ASSERT(m_verifier.isSafeToUse());
#endif
    return m_refCount;
  }

 protected:
  RefCountedBase()
      : m_refCount(1)
#if ENABLE(SECURITY_ASSERT)
        ,
        m_deletionHasBegun(false)
#endif
#if CHECK_REF_COUNTED_LIFECYCLE
        ,
        m_adoptionIsRequired(true)
#endif
  {
  }

  ~RefCountedBase() {
    ASSERT_WITH_SECURITY_IMPLICATION(m_deletionHasBegun);
#if CHECK_REF_COUNTED_LIFECYCLE
    ASSERT(!m_adoptionIsRequired);
#endif
  }

  // Returns whether the pointer should be freed or not.
  bool derefBase() {
    ASSERT_WITH_SECURITY_IMPLICATION(!m_deletionHasBegun);
#if CHECK_REF_COUNTED_LIFECYCLE
    ASSERT(m_verifier.isSafeToUse());
    ASSERT(!m_adoptionIsRequired);
#endif

    ASSERT(m_refCount > 0);
    --m_refCount;
    if (!m_refCount) {
#if ENABLE(SECURITY_ASSERT)
      m_deletionHasBegun = true;
#endif
      return true;
    }

#if CHECK_REF_COUNTED_LIFECYCLE
    // Stop thread verification when the ref goes to 1 because it
    // is safe to be passed to another thread at this point.
    if (m_refCount == 1)
      m_verifier.setShared(false);
#endif
    return false;
  }

#if CHECK_REF_COUNTED_LIFECYCLE
  bool deletionHasBegun() const { return m_deletionHasBegun; }
#endif

 private:
#if CHECK_REF_COUNTED_LIFECYCLE || ENABLE(SECURITY_ASSERT)
  friend void adopted(RefCountedBase*);
#endif

  int m_refCount;
#if ENABLE(SECURITY_ASSERT)
  bool m_deletionHasBegun;
#endif
#if CHECK_REF_COUNTED_LIFECYCLE
  bool m_adoptionIsRequired;
  ThreadRestrictionVerifier m_verifier;
#endif
};

#if CHECK_REF_COUNTED_LIFECYCLE || ENABLE(SECURITY_ASSERT)
inline void adopted(RefCountedBase* object) {
  if (!object)
    return;
  ASSERT_WITH_SECURITY_IMPLICATION(!object->m_deletionHasBegun);
#if CHECK_REF_COUNTED_LIFECYCLE
  object->m_adoptionIsRequired = false;
#endif
}
#endif

template <typename T>
class RefCounted : public RefCountedBase {
  WTF_MAKE_NONCOPYABLE(RefCounted);
  WTF_MAKE_FAST_ALLOCATED;

 public:
  void deref() {
    if (derefBase())
      delete static_cast<T*>(this);
  }

 protected:
#ifdef ENABLE_INSTANCE_COUNTER
  RefCounted() { incrementInstanceCount<T>(static_cast<T*>(this)); }

  ~RefCounted() { decrementInstanceCount<T>(static_cast<T*>(this)); }
#else
  RefCounted() {}
#endif
};

}  // namespace WTF

using WTF::RefCounted;

#endif  // SKY_ENGINE_WTF_REFCOUNTED_H_