The Tor Browser: mfbt/RefPtr.h@fc2d59ddac77 (annotated)

mfbt/RefPtr.h@fc2d59ddac77 (annotated)

mfbt/RefPtr.h

Wed, 31 Dec 2014 07:22:50 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 07:22:50 +0100
branch: TOR_BUG_3246
changeset 4: fc2d59ddac77
permissions: -rw-r--r--

Correct previous dual key logic pending first delivery installment.

 /* -*- 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 */

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mfbt/RefPtr.h@fc2d59ddac77 (annotated)

mfbt/RefPtr.h