gecko-dev/js/public/RefCounted.h

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#ifndef js_RefCounted_h
#define js_RefCounted_h

#include "mozilla/Atomics.h"
#include "mozilla/RefCountType.h"

#include "js/Utility.h"

// These types implement the same interface as mozilla::(Atomic)RefCounted and
// must be used instead of mozilla::(Atomic)RefCounted for everything in
// SpiderMonkey. There are two reasons:
//  - Release() needs to call js_delete, not delete
//  - SpiderMonkey does not have MOZILLA_INTERNAL_API defined which can lead
//    to ODR violations that show up as spurious leak reports when ref-counted
//    types are allocated by SpiderMonkey and released by Gecko (or vice versa).

namespace js {

template <typename T>
class RefCounted {
  static const MozRefCountType DEAD = 0xffffdead;

 protected:
  RefCounted() : mRefCnt(0) {}
  ~RefCounted() { MOZ_ASSERT(mRefCnt == DEAD); }

 public:
  void AddRef() const {
    MOZ_ASSERT(int32_t(mRefCnt) >= 0);
    ++mRefCnt;
  }

  void Release() const {
    MOZ_ASSERT(int32_t(mRefCnt) > 0);
    MozRefCountType cnt = --mRefCnt;
    if (0 == cnt) {
#ifdef DEBUG
      mRefCnt = DEAD;
#endif
      js_delete(const_cast<T*>(static_cast<const T*>(this)));
    }
  }

 private:
  mutable MozRefCountType mRefCnt;
};

template <typename T>
class AtomicRefCounted {
  // On 64-bit systems, if the refcount type is small (say, 32 bits), there's
  // a risk that it could overflow.  So require it to be large enough.

  static_assert(sizeof(MozRefCountType) == sizeof(uintptr_t),
                "You're at risk for ref count overflow.");

  static const MozRefCountType DEAD = ~MozRefCountType(0xffff) | 0xdead;

 protected:
  AtomicRefCounted() = default;
  ~AtomicRefCounted() { MOZ_ASSERT(mRefCnt == DEAD); }

 public:
  void AddRef() const {
    ++mRefCnt;
    MOZ_ASSERT(mRefCnt != DEAD);
  }

  void Release() const {
    MOZ_ASSERT(mRefCnt != 0);
    MozRefCountType cnt = --mRefCnt;
    if (0 == cnt) {
#ifdef DEBUG
      mRefCnt = DEAD;
#endif
      js_delete(const_cast<T*>(static_cast<const T*>(this)));
    }
  }

 private:
  mutable mozilla::Atomic<MozRefCountType> mRefCnt{0};
};

}  // namespace js

#endif /* js_RefCounted_h */