js/public/RefCounted.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef js_RefCounted_h
   8 #define js_RefCounted_h
   9
  10 #include "mozilla/Atomics.h"
  11 #include "mozilla/RefCountType.h"
  12
  13 #include "js/Utility.h"
  14
  15 // These types implement the same interface as mozilla::(Atomic)RefCounted and
  16 // must be used instead of mozilla::(Atomic)RefCounted for everything in
  17 // SpiderMonkey. There are two reasons:
  18 //  - Release() needs to call js_delete, not delete
  19 //  - SpiderMonkey does not have MOZILLA_INTERNAL_API defined which can lead
  20 //    to ODR violations that show up as spurious leak reports when ref-counted
  21 //    types are allocated by SpiderMonkey and released by Gecko (or vice versa).
  22
  23 namespace js {
  24
  25 template <typename T>
  26 class RefCounted {
  27   static const MozRefCountType DEAD = 0xffffdead;
  28
  29  protected:
  30   RefCounted() : mRefCnt(0) {}
  31   ~RefCounted() { MOZ_ASSERT(mRefCnt == DEAD); }
  32
  33  public:
  34   void AddRef() const {
  35     MOZ_ASSERT(int32_t(mRefCnt) >= 0);
  36     ++mRefCnt;
  37   }
  38
  39   void Release() const {
  40     MOZ_ASSERT(int32_t(mRefCnt) > 0);
  41     MozRefCountType cnt = --mRefCnt;
  42     if (0 == cnt) {
  43 #ifdef DEBUG
  44       mRefCnt = DEAD;
  45 #endif
  46       js_delete(const_cast<T*>(static_cast<const T*>(this)));
  47     }
  48   }
  49
  50  private:
  51   mutable MozRefCountType mRefCnt;
  52 };
  53
  54 template <typename T>
  55 class AtomicRefCounted {
  56   // On 64-bit systems, if the refcount type is small (say, 32 bits), there's
  57   // a risk that it could overflow.  So require it to be large enough.
  58
  59   static_assert(sizeof(MozRefCountType) == sizeof(uintptr_t),
  60                 "You're at risk for ref count overflow.");
  61
  62   static const MozRefCountType DEAD = ~MozRefCountType(0xffff) | 0xdead;
  63
  64  protected:
  65   AtomicRefCounted() = default;
  66   ~AtomicRefCounted() { MOZ_ASSERT(mRefCnt == DEAD); }
  67
  68  public:
  69   void AddRef() const {
  70     ++mRefCnt;
  71     MOZ_ASSERT(mRefCnt != DEAD);
  72   }
  73
  74   void Release() const {
  75     MOZ_ASSERT(mRefCnt != 0);
  76     MozRefCountType cnt = --mRefCnt;
  77     if (0 == cnt) {
  78 #ifdef DEBUG
  79       mRefCnt = DEAD;
  80 #endif
  81       js_delete(const_cast<T*>(static_cast<const T*>(this)));
  82     }
  83   }
  84
  85   bool hasOneRef() const {
  86     MOZ_ASSERT(mRefCnt > 0);
  87     return mRefCnt == 1;
  88   }
  89
  90  private:
  91   mutable mozilla::Atomic<MozRefCountType> mRefCnt{0};
  92 };
  93
  94 }  // namespace js
  95
  96 #endif /* js_RefCounted_h */