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 /* -*- 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/. */

 /* Helpers for defining and using refcounted objects. */

 #ifndef mozilla_RefPtr_h

 #define mozilla_RefPtr_h

 #include "mozilla/Assertions.h"

 #include "mozilla/Atomics.h"

 #include "mozilla/Attributes.h"

 #include "mozilla/RefCountType.h"

 #include "mozilla/TypeTraits.h"

 #if defined(MOZILLA_INTERNAL_API)

 #include "nsXPCOM.h"

 #endif

 #if defined(MOZILLA_INTERNAL_API) && (defined(DEBUG) || defined(FORCE_BUILD_REFCNT_LOGGING))

 #define MOZ_REFCOUNTED_LEAK_CHECKING

 #endif

 namespace mozilla {

 template<typename T> class RefCounted;

 template<typename T> class RefPtr;

 template<typename T> class TemporaryRef;

 template<typename T> class OutParamRef;

 template<typename T> OutParamRef<T> byRef(RefPtr<T>&);

 /**

  * RefCounted<T> is a sort of a "mixin" for a class T.  RefCounted

  * manages, well, refcounting for T, and because RefCounted is

  * parameterized on T, RefCounted<T> can call T's destructor directly.

  * This means T doesn't need to have a virtual dtor and so doesn't

  * need a vtable.

  *

  * RefCounted<T> is created with refcount == 0.  Newly-allocated

  * RefCounted<T> must immediately be assigned to a RefPtr to make the

  * refcount > 0.  It's an error to allocate and free a bare

  * RefCounted<T>, i.e. outside of the RefPtr machinery.  Attempts to

  * do so will abort DEBUG builds.

  *

  * Live RefCounted<T> have refcount > 0.  The lifetime (refcounts) of

  * live RefCounted<T> are controlled by RefPtr<T> and

  * RefPtr<super/subclass of T>.  Upon a transition from refcounted==1

  * to 0, the RefCounted<T> "dies" and is destroyed.  The "destroyed"

  * state is represented in DEBUG builds by refcount==0xffffdead.  This

  * state distinguishes use-before-ref (refcount==0) from

  * use-after-destroy (refcount==0xffffdead).

  *

  * Note that when deriving from RefCounted or AtomicRefCounted, you

  * should add MOZ_DECLARE_REFCOUNTED_TYPENAME(ClassName) to the public

  * section of your class, where ClassName is the name of your class.

  */

 namespace detail {

 #ifdef DEBUG

 const MozRefCountType DEAD = 0xffffdead;

 #endif

 // When building code that gets compiled into Gecko, try to use the

 // trace-refcount leak logging facilities.

 #ifdef MOZ_REFCOUNTED_LEAK_CHECKING

 class RefCountLogger

 {

   public:

     static void logAddRef(const void* aPointer, MozRefCountType aRefCount,

                           const char* aTypeName, uint32_t aInstanceSize)

     {

       MOZ_ASSERT(aRefCount != DEAD);

       NS_LogAddRef(const_cast<void*>(aPointer), aRefCount, aTypeName, aInstanceSize);

     }

     static void logRelease(const void* aPointer, MozRefCountType aRefCount,

                            const char* aTypeName)

     {

       MOZ_ASSERT(aRefCount != DEAD);

       NS_LogRelease(const_cast<void*>(aPointer), aRefCount, aTypeName);

     }

 };

 #endif

 // This is used WeakPtr.h as well as this file.

 enum RefCountAtomicity

 {

   AtomicRefCount,

   NonAtomicRefCount

 };

 template<typename T, RefCountAtomicity Atomicity>

 class RefCounted

 {

     friend class RefPtr<T>;

   protected:

     RefCounted() : refCnt(0) { }

     ~RefCounted() {

       MOZ_ASSERT(refCnt == detail::DEAD);

     }

   public:

     // Compatibility with nsRefPtr.

     void AddRef() const {

       // Note: this method must be thread safe for AtomicRefCounted.

       MOZ_ASSERT(int32_t(refCnt) >= 0);

 #ifndef MOZ_REFCOUNTED_LEAK_CHECKING

       ++refCnt;

 #else

       const char* type = static_cast<const T*>(this)->typeName();

       uint32_t size = static_cast<const T*>(this)->typeSize();

       const void* ptr = static_cast<const T*>(this);

       MozRefCountType cnt = ++refCnt;

       detail::RefCountLogger::logAddRef(ptr, cnt, type, size);

 #endif

     }

     void Release() const {

       // Note: this method must be thread safe for AtomicRefCounted.

       MOZ_ASSERT(int32_t(refCnt) > 0);

 #ifndef MOZ_REFCOUNTED_LEAK_CHECKING

       MozRefCountType cnt = --refCnt;

 #else

       const char* type = static_cast<const T*>(this)->typeName();

       const void* ptr = static_cast<const T*>(this);

       MozRefCountType cnt = --refCnt;

       // Note: it's not safe to touch |this| after decrementing the refcount,

       // except for below.

       detail::RefCountLogger::logRelease(ptr, cnt, type);

 #endif

       if (0 == cnt) {

         // Because we have atomically decremented the refcount above, only

         // one thread can get a 0 count here, so as long as we can assume that

         // everything else in the system is accessing this object through

         // RefPtrs, it's safe to access |this| here.

 #ifdef DEBUG

         refCnt = detail::DEAD;

 #endif

         delete static_cast<const T*>(this);

       }

     }

     // Compatibility with wtf::RefPtr.

     void ref() { AddRef(); }

     void deref() { Release(); }

     MozRefCountType refCount() const { return refCnt; }

     bool hasOneRef() const {

       MOZ_ASSERT(refCnt > 0);

       return refCnt == 1;

     }

   private:

     mutable typename Conditional<Atomicity == AtomicRefCount, Atomic<MozRefCountType>, MozRefCountType>::Type refCnt;

 };

 #ifdef MOZ_REFCOUNTED_LEAK_CHECKING

 #define MOZ_DECLARE_REFCOUNTED_TYPENAME(T) \

   const char* typeName() const { return #T; } \

   size_t typeSize() const { return sizeof(*this); }

 #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T) \

   virtual const char* typeName() const { return #T; } \

   virtual size_t typeSize() const { return sizeof(*this); }

 #else

 #define MOZ_DECLARE_REFCOUNTED_TYPENAME(T)

 #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T)

 #endif

 }

 template<typename T>

 class RefCounted : public detail::RefCounted<T, detail::NonAtomicRefCount>

 {

   public:

     ~RefCounted() {

       static_assert(IsBaseOf<RefCounted, T>::value,

                     "T must derive from RefCounted<T>");

     }

 };

 /**

  * AtomicRefCounted<T> is like RefCounted<T>, with an atomically updated

  * reference counter.

  */

 template<typename T>

 class AtomicRefCounted : public detail::RefCounted<T, detail::AtomicRefCount>

 {

   public:

     ~AtomicRefCounted() {

       static_assert(IsBaseOf<AtomicRefCounted, T>::value,

                     "T must derive from AtomicRefCounted<T>");

     }

 };

 /**

  * RefPtr points to a refcounted thing that has AddRef and Release

  * methods to increase/decrease the refcount, respectively.  After a

  * RefPtr<T> is assigned a T*, the T* can be used through the RefPtr

  * as if it were a T*.

  *

  * A RefPtr can forget its underlying T*, which results in the T*

  * being wrapped in a temporary object until the T* is either

  * re-adopted from or released by the temporary.

  */

 template<typename T>

 class RefPtr

 {

     // To allow them to use unref()

     friend class TemporaryRef<T>;

     friend class OutParamRef<T>;

     struct DontRef {};

   public:

     RefPtr() : ptr(0) { }

     RefPtr(const RefPtr& o) : ptr(ref(o.ptr)) {}

     RefPtr(const TemporaryRef<T>& o) : ptr(o.drop()) {}

     RefPtr(T* t) : ptr(ref(t)) {}

     template<typename U>

     RefPtr(const RefPtr<U>& o) : ptr(ref(o.get())) {}

     ~RefPtr() { unref(ptr); }

     RefPtr& operator=(const RefPtr& o) {

       assign(ref(o.ptr));

       return *this;

     }

     RefPtr& operator=(const TemporaryRef<T>& o) {

       assign(o.drop());

       return *this;

     }

     RefPtr& operator=(T* t) {

       assign(ref(t));

       return *this;

     }

     template<typename U>

     RefPtr& operator=(const RefPtr<U>& o) {

       assign(ref(o.get()));

       return *this;

     }

     TemporaryRef<T> forget() {

       T* tmp = ptr;

       ptr = 0;

       return TemporaryRef<T>(tmp, DontRef());

     }

     T* get() const { return ptr; }

     operator T*() const { return ptr; }

     T* operator->() const { return ptr; }

     T& operator*() const { return *ptr; }

     template<typename U>

     operator TemporaryRef<U>() { return TemporaryRef<U>(ptr); }

   private:

     void assign(T* t) {

       unref(ptr);

       ptr = t;

     }

     T* ptr;

     static MOZ_ALWAYS_INLINE T* ref(T* t) {

       if (t)

         t->AddRef();

       return t;

     }

     static MOZ_ALWAYS_INLINE void unref(T* t) {

       if (t)

         t->Release();

     }

 };

 /**

  * TemporaryRef<T> represents an object that holds a temporary

  * reference to a T.  TemporaryRef objects can't be manually ref'd or

  * unref'd (being temporaries, not lvalues), so can only relinquish

  * references to other objects, or unref on destruction.

  */

 template<typename T>

 class TemporaryRef

 {

     // To allow it to construct TemporaryRef from a bare T*

     friend class RefPtr<T>;

     typedef typename RefPtr<T>::DontRef DontRef;

   public:

     TemporaryRef(T* t) : ptr(RefPtr<T>::ref(t)) {}

     TemporaryRef(const TemporaryRef& o) : ptr(o.drop()) {}

     template<typename U>

     TemporaryRef(const TemporaryRef<U>& o) : ptr(o.drop()) {}

     ~TemporaryRef() { RefPtr<T>::unref(ptr); }

     T* drop() const {

       T* tmp = ptr;

       ptr = 0;

       return tmp;

     }

   private:

     TemporaryRef(T* t, const DontRef&) : ptr(t) {}

     mutable T* ptr;

     TemporaryRef() MOZ_DELETE;

     void operator=(const TemporaryRef&) MOZ_DELETE;

 };

 /**

  * OutParamRef is a wrapper that tracks a refcounted pointer passed as

  * an outparam argument to a function.  OutParamRef implements COM T**

  * outparam semantics: this requires the callee to AddRef() the T*

  * returned through the T** outparam on behalf of the caller.  This

  * means the caller (through OutParamRef) must Release() the old

  * object contained in the tracked RefPtr.  It's OK if the callee

  * returns the same T* passed to it through the T** outparam, as long

  * as the callee obeys the COM discipline.

  *

  * Prefer returning TemporaryRef<T> from functions over creating T**

  * outparams and passing OutParamRef<T> to T**.  Prefer RefPtr<T>*

  * outparams over T** outparams.

  */

 template<typename T>

 class OutParamRef

 {

     friend OutParamRef byRef<T>(RefPtr<T>&);

   public:

     ~OutParamRef() {

       RefPtr<T>::unref(refPtr.ptr);

       refPtr.ptr = tmp;

     }

     operator T**() { return &tmp; }

   private:

     OutParamRef(RefPtr<T>& p) : refPtr(p), tmp(p.get()) {}

     RefPtr<T>& refPtr;

     T* tmp;

     OutParamRef() MOZ_DELETE;

     OutParamRef& operator=(const OutParamRef&) MOZ_DELETE;

 };

 /**

  * byRef cooperates with OutParamRef to implement COM outparam semantics.

  */

 template<typename T>

 OutParamRef<T>

 byRef(RefPtr<T>& ptr)

 {

   return OutParamRef<T>(ptr);

 }

 } // namespace mozilla

 #if 0

 // Command line that builds these tests

 //

 //   cp RefPtr.h test.cc && g++ -g -Wall -pedantic -DDEBUG -o test test.cc && ./test

 using namespace mozilla;

 struct Foo : public RefCounted<Foo>

 {

   MOZ_DECLARE_REFCOUNTED_TYPENAME(Foo)

   Foo() : dead(false) { }

   ~Foo() {

     MOZ_ASSERT(!dead);

     dead = true;

     numDestroyed++;

   }

   bool dead;

   static int numDestroyed;

 };

 int Foo::numDestroyed;

 struct Bar : public Foo { };

 TemporaryRef<Foo>

 NewFoo()

 {

   return RefPtr<Foo>(new Foo());

 }

 TemporaryRef<Foo>

 NewBar()

 {

   return new Bar();

 }

 void

 GetNewFoo(Foo** f)

 {

   *f = new Bar();

   // Kids, don't try this at home

   (*f)->AddRef();

 }

 void

 GetPassedFoo(Foo** f)

 {

   // Kids, don't try this at home

   (*f)->AddRef();

 }

 void

 GetNewFoo(RefPtr<Foo>* f)

 {

   *f = new Bar();

 }

 void

 GetPassedFoo(RefPtr<Foo>* f)

 {}

 TemporaryRef<Foo>

 GetNullFoo()

 {

   return 0;

 }

 int

 main(int argc, char** argv)

 {

   // This should blow up

 //    Foo* f = new Foo(); delete f;

   MOZ_ASSERT(0 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = new Foo();

     MOZ_ASSERT(f->refCount() == 1);

   }

   MOZ_ASSERT(1 == Foo::numDestroyed);

   {

     RefPtr<Foo> f1 = NewFoo();

     RefPtr<Foo> f2(NewFoo());

     MOZ_ASSERT(1 == Foo::numDestroyed);

   }

   MOZ_ASSERT(3 == Foo::numDestroyed);

   {

     RefPtr<Foo> b = NewBar();

     MOZ_ASSERT(3 == Foo::numDestroyed);

   }

   MOZ_ASSERT(4 == Foo::numDestroyed);

   {

     RefPtr<Foo> f1;

     {

       f1 = new Foo();

       RefPtr<Foo> f2(f1);

       RefPtr<Foo> f3 = f2;

       MOZ_ASSERT(4 == Foo::numDestroyed);

     }

     MOZ_ASSERT(4 == Foo::numDestroyed);

   }

   MOZ_ASSERT(5 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = new Foo();

     f.forget();

     MOZ_ASSERT(6 == Foo::numDestroyed);

   }

   {

     RefPtr<Foo> f = new Foo();

     GetNewFoo(byRef(f));

     MOZ_ASSERT(7 == Foo::numDestroyed);

   }

   MOZ_ASSERT(8 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = new Foo();

     GetPassedFoo(byRef(f));

     MOZ_ASSERT(8 == Foo::numDestroyed);

   }

   MOZ_ASSERT(9 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = new Foo();

     GetNewFoo(&f);

     MOZ_ASSERT(10 == Foo::numDestroyed);

   }

   MOZ_ASSERT(11 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = new Foo();

     GetPassedFoo(&f);

     MOZ_ASSERT(11 == Foo::numDestroyed);

   }

   MOZ_ASSERT(12 == Foo::numDestroyed);

   {

     RefPtr<Foo> f1 = new Bar();

   }

   MOZ_ASSERT(13 == Foo::numDestroyed);

   {

     RefPtr<Foo> f = GetNullFoo();

     MOZ_ASSERT(13 == Foo::numDestroyed);

   }

   MOZ_ASSERT(13 == Foo::numDestroyed);

   return 0;

 }

 #endif

 #endif /* mozilla_RefPtr_h */