michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /* Helpers for defining and using refcounted objects. */
michael@0: 
michael@0: #ifndef mozilla_RefPtr_h
michael@0: #define mozilla_RefPtr_h
michael@0: 
michael@0: #include "mozilla/Assertions.h"
michael@0: #include "mozilla/Atomics.h"
michael@0: #include "mozilla/Attributes.h"
michael@0: #include "mozilla/RefCountType.h"
michael@0: #include "mozilla/TypeTraits.h"
michael@0: #if defined(MOZILLA_INTERNAL_API)
michael@0: #include "nsXPCOM.h"
michael@0: #endif
michael@0: 
michael@0: #if defined(MOZILLA_INTERNAL_API) && (defined(DEBUG) || defined(FORCE_BUILD_REFCNT_LOGGING))
michael@0: #define MOZ_REFCOUNTED_LEAK_CHECKING
michael@0: #endif
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: template<typename T> class RefCounted;
michael@0: template<typename T> class RefPtr;
michael@0: template<typename T> class TemporaryRef;
michael@0: template<typename T> class OutParamRef;
michael@0: template<typename T> OutParamRef<T> byRef(RefPtr<T>&);
michael@0: 
michael@0: /**
michael@0:  * RefCounted<T> is a sort of a "mixin" for a class T.  RefCounted
michael@0:  * manages, well, refcounting for T, and because RefCounted is
michael@0:  * parameterized on T, RefCounted<T> can call T's destructor directly.
michael@0:  * This means T doesn't need to have a virtual dtor and so doesn't
michael@0:  * need a vtable.
michael@0:  *
michael@0:  * RefCounted<T> is created with refcount == 0.  Newly-allocated
michael@0:  * RefCounted<T> must immediately be assigned to a RefPtr to make the
michael@0:  * refcount > 0.  It's an error to allocate and free a bare
michael@0:  * RefCounted<T>, i.e. outside of the RefPtr machinery.  Attempts to
michael@0:  * do so will abort DEBUG builds.
michael@0:  *
michael@0:  * Live RefCounted<T> have refcount > 0.  The lifetime (refcounts) of
michael@0:  * live RefCounted<T> are controlled by RefPtr<T> and
michael@0:  * RefPtr<super/subclass of T>.  Upon a transition from refcounted==1
michael@0:  * to 0, the RefCounted<T> "dies" and is destroyed.  The "destroyed"
michael@0:  * state is represented in DEBUG builds by refcount==0xffffdead.  This
michael@0:  * state distinguishes use-before-ref (refcount==0) from
michael@0:  * use-after-destroy (refcount==0xffffdead).
michael@0:  *
michael@0:  * Note that when deriving from RefCounted or AtomicRefCounted, you
michael@0:  * should add MOZ_DECLARE_REFCOUNTED_TYPENAME(ClassName) to the public
michael@0:  * section of your class, where ClassName is the name of your class.
michael@0:  */
michael@0: namespace detail {
michael@0: #ifdef DEBUG
michael@0: const MozRefCountType DEAD = 0xffffdead;
michael@0: #endif
michael@0: 
michael@0: // When building code that gets compiled into Gecko, try to use the
michael@0: // trace-refcount leak logging facilities.
michael@0: #ifdef MOZ_REFCOUNTED_LEAK_CHECKING
michael@0: class RefCountLogger
michael@0: {
michael@0:   public:
michael@0:     static void logAddRef(const void* aPointer, MozRefCountType aRefCount,
michael@0:                           const char* aTypeName, uint32_t aInstanceSize)
michael@0:     {
michael@0:       MOZ_ASSERT(aRefCount != DEAD);
michael@0:       NS_LogAddRef(const_cast<void*>(aPointer), aRefCount, aTypeName, aInstanceSize);
michael@0:     }
michael@0: 
michael@0:     static void logRelease(const void* aPointer, MozRefCountType aRefCount,
michael@0:                            const char* aTypeName)
michael@0:     {
michael@0:       MOZ_ASSERT(aRefCount != DEAD);
michael@0:       NS_LogRelease(const_cast<void*>(aPointer), aRefCount, aTypeName);
michael@0:     }
michael@0: };
michael@0: #endif
michael@0: 
michael@0: // This is used WeakPtr.h as well as this file.
michael@0: enum RefCountAtomicity
michael@0: {
michael@0:   AtomicRefCount,
michael@0:   NonAtomicRefCount
michael@0: };
michael@0: 
michael@0: template<typename T, RefCountAtomicity Atomicity>
michael@0: class RefCounted
michael@0: {
michael@0:     friend class RefPtr<T>;
michael@0: 
michael@0:   protected:
michael@0:     RefCounted() : refCnt(0) { }
michael@0:     ~RefCounted() {
michael@0:       MOZ_ASSERT(refCnt == detail::DEAD);
michael@0:     }
michael@0: 
michael@0:   public:
michael@0:     // Compatibility with nsRefPtr.
michael@0:     void AddRef() const {
michael@0:       // Note: this method must be thread safe for AtomicRefCounted.
michael@0:       MOZ_ASSERT(int32_t(refCnt) >= 0);
michael@0: #ifndef MOZ_REFCOUNTED_LEAK_CHECKING
michael@0:       ++refCnt;
michael@0: #else
michael@0:       const char* type = static_cast<const T*>(this)->typeName();
michael@0:       uint32_t size = static_cast<const T*>(this)->typeSize();
michael@0:       const void* ptr = static_cast<const T*>(this);
michael@0:       MozRefCountType cnt = ++refCnt;
michael@0:       detail::RefCountLogger::logAddRef(ptr, cnt, type, size);
michael@0: #endif
michael@0:     }
michael@0: 
michael@0:     void Release() const {
michael@0:       // Note: this method must be thread safe for AtomicRefCounted.
michael@0:       MOZ_ASSERT(int32_t(refCnt) > 0);
michael@0: #ifndef MOZ_REFCOUNTED_LEAK_CHECKING
michael@0:       MozRefCountType cnt = --refCnt;
michael@0: #else
michael@0:       const char* type = static_cast<const T*>(this)->typeName();
michael@0:       const void* ptr = static_cast<const T*>(this);
michael@0:       MozRefCountType cnt = --refCnt;
michael@0:       // Note: it's not safe to touch |this| after decrementing the refcount,
michael@0:       // except for below.
michael@0:       detail::RefCountLogger::logRelease(ptr, cnt, type);
michael@0: #endif
michael@0:       if (0 == cnt) {
michael@0:         // Because we have atomically decremented the refcount above, only
michael@0:         // one thread can get a 0 count here, so as long as we can assume that
michael@0:         // everything else in the system is accessing this object through
michael@0:         // RefPtrs, it's safe to access |this| here.
michael@0: #ifdef DEBUG
michael@0:         refCnt = detail::DEAD;
michael@0: #endif
michael@0:         delete static_cast<const T*>(this);
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     // Compatibility with wtf::RefPtr.
michael@0:     void ref() { AddRef(); }
michael@0:     void deref() { Release(); }
michael@0:     MozRefCountType refCount() const { return refCnt; }
michael@0:     bool hasOneRef() const {
michael@0:       MOZ_ASSERT(refCnt > 0);
michael@0:       return refCnt == 1;
michael@0:     }
michael@0: 
michael@0:   private:
michael@0:     mutable typename Conditional<Atomicity == AtomicRefCount, Atomic<MozRefCountType>, MozRefCountType>::Type refCnt;
michael@0: };
michael@0: 
michael@0: #ifdef MOZ_REFCOUNTED_LEAK_CHECKING
michael@0: #define MOZ_DECLARE_REFCOUNTED_TYPENAME(T) \
michael@0:   const char* typeName() const { return #T; } \
michael@0:   size_t typeSize() const { return sizeof(*this); }
michael@0: 
michael@0: #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T) \
michael@0:   virtual const char* typeName() const { return #T; } \
michael@0:   virtual size_t typeSize() const { return sizeof(*this); }
michael@0: #else
michael@0: #define MOZ_DECLARE_REFCOUNTED_TYPENAME(T)
michael@0: #define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T)
michael@0: #endif
michael@0: 
michael@0: }
michael@0: 
michael@0: template<typename T>
michael@0: class RefCounted : public detail::RefCounted<T, detail::NonAtomicRefCount>
michael@0: {
michael@0:   public:
michael@0:     ~RefCounted() {
michael@0:       static_assert(IsBaseOf<RefCounted, T>::value,
michael@0:                     "T must derive from RefCounted<T>");
michael@0:     }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * AtomicRefCounted<T> is like RefCounted<T>, with an atomically updated
michael@0:  * reference counter.
michael@0:  */
michael@0: template<typename T>
michael@0: class AtomicRefCounted : public detail::RefCounted<T, detail::AtomicRefCount>
michael@0: {
michael@0:   public:
michael@0:     ~AtomicRefCounted() {
michael@0:       static_assert(IsBaseOf<AtomicRefCounted, T>::value,
michael@0:                     "T must derive from AtomicRefCounted<T>");
michael@0:     }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * RefPtr points to a refcounted thing that has AddRef and Release
michael@0:  * methods to increase/decrease the refcount, respectively.  After a
michael@0:  * RefPtr<T> is assigned a T*, the T* can be used through the RefPtr
michael@0:  * as if it were a T*.
michael@0:  *
michael@0:  * A RefPtr can forget its underlying T*, which results in the T*
michael@0:  * being wrapped in a temporary object until the T* is either
michael@0:  * re-adopted from or released by the temporary.
michael@0:  */
michael@0: template<typename T>
michael@0: class RefPtr
michael@0: {
michael@0:     // To allow them to use unref()
michael@0:     friend class TemporaryRef<T>;
michael@0:     friend class OutParamRef<T>;
michael@0: 
michael@0:     struct DontRef {};
michael@0: 
michael@0:   public:
michael@0:     RefPtr() : ptr(0) { }
michael@0:     RefPtr(const RefPtr& o) : ptr(ref(o.ptr)) {}
michael@0:     RefPtr(const TemporaryRef<T>& o) : ptr(o.drop()) {}
michael@0:     RefPtr(T* t) : ptr(ref(t)) {}
michael@0: 
michael@0:     template<typename U>
michael@0:     RefPtr(const RefPtr<U>& o) : ptr(ref(o.get())) {}
michael@0: 
michael@0:     ~RefPtr() { unref(ptr); }
michael@0: 
michael@0:     RefPtr& operator=(const RefPtr& o) {
michael@0:       assign(ref(o.ptr));
michael@0:       return *this;
michael@0:     }
michael@0:     RefPtr& operator=(const TemporaryRef<T>& o) {
michael@0:       assign(o.drop());
michael@0:       return *this;
michael@0:     }
michael@0:     RefPtr& operator=(T* t) {
michael@0:       assign(ref(t));
michael@0:       return *this;
michael@0:     }
michael@0: 
michael@0:     template<typename U>
michael@0:     RefPtr& operator=(const RefPtr<U>& o) {
michael@0:       assign(ref(o.get()));
michael@0:       return *this;
michael@0:     }
michael@0: 
michael@0:     TemporaryRef<T> forget() {
michael@0:       T* tmp = ptr;
michael@0:       ptr = 0;
michael@0:       return TemporaryRef<T>(tmp, DontRef());
michael@0:     }
michael@0: 
michael@0:     T* get() const { return ptr; }
michael@0:     operator T*() const { return ptr; }
michael@0:     T* operator->() const { return ptr; }
michael@0:     T& operator*() const { return *ptr; }
michael@0:     template<typename U>
michael@0:     operator TemporaryRef<U>() { return TemporaryRef<U>(ptr); }
michael@0: 
michael@0:   private:
michael@0:     void assign(T* t) {
michael@0:       unref(ptr);
michael@0:       ptr = t;
michael@0:     }
michael@0: 
michael@0:     T* ptr;
michael@0: 
michael@0:     static MOZ_ALWAYS_INLINE T* ref(T* t) {
michael@0:       if (t)
michael@0:         t->AddRef();
michael@0:       return t;
michael@0:     }
michael@0: 
michael@0:     static MOZ_ALWAYS_INLINE void unref(T* t) {
michael@0:       if (t)
michael@0:         t->Release();
michael@0:     }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * TemporaryRef<T> represents an object that holds a temporary
michael@0:  * reference to a T.  TemporaryRef objects can't be manually ref'd or
michael@0:  * unref'd (being temporaries, not lvalues), so can only relinquish
michael@0:  * references to other objects, or unref on destruction.
michael@0:  */
michael@0: template<typename T>
michael@0: class TemporaryRef
michael@0: {
michael@0:     // To allow it to construct TemporaryRef from a bare T*
michael@0:     friend class RefPtr<T>;
michael@0: 
michael@0:     typedef typename RefPtr<T>::DontRef DontRef;
michael@0: 
michael@0:   public:
michael@0:     TemporaryRef(T* t) : ptr(RefPtr<T>::ref(t)) {}
michael@0:     TemporaryRef(const TemporaryRef& o) : ptr(o.drop()) {}
michael@0: 
michael@0:     template<typename U>
michael@0:     TemporaryRef(const TemporaryRef<U>& o) : ptr(o.drop()) {}
michael@0: 
michael@0:     ~TemporaryRef() { RefPtr<T>::unref(ptr); }
michael@0: 
michael@0:     T* drop() const {
michael@0:       T* tmp = ptr;
michael@0:       ptr = 0;
michael@0:       return tmp;
michael@0:     }
michael@0: 
michael@0:   private:
michael@0:     TemporaryRef(T* t, const DontRef&) : ptr(t) {}
michael@0: 
michael@0:     mutable T* ptr;
michael@0: 
michael@0:     TemporaryRef() MOZ_DELETE;
michael@0:     void operator=(const TemporaryRef&) MOZ_DELETE;
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * OutParamRef is a wrapper that tracks a refcounted pointer passed as
michael@0:  * an outparam argument to a function.  OutParamRef implements COM T**
michael@0:  * outparam semantics: this requires the callee to AddRef() the T*
michael@0:  * returned through the T** outparam on behalf of the caller.  This
michael@0:  * means the caller (through OutParamRef) must Release() the old
michael@0:  * object contained in the tracked RefPtr.  It's OK if the callee
michael@0:  * returns the same T* passed to it through the T** outparam, as long
michael@0:  * as the callee obeys the COM discipline.
michael@0:  *
michael@0:  * Prefer returning TemporaryRef<T> from functions over creating T**
michael@0:  * outparams and passing OutParamRef<T> to T**.  Prefer RefPtr<T>*
michael@0:  * outparams over T** outparams.
michael@0:  */
michael@0: template<typename T>
michael@0: class OutParamRef
michael@0: {
michael@0:     friend OutParamRef byRef<T>(RefPtr<T>&);
michael@0: 
michael@0:   public:
michael@0:     ~OutParamRef() {
michael@0:       RefPtr<T>::unref(refPtr.ptr);
michael@0:       refPtr.ptr = tmp;
michael@0:     }
michael@0: 
michael@0:     operator T**() { return &tmp; }
michael@0: 
michael@0:   private:
michael@0:     OutParamRef(RefPtr<T>& p) : refPtr(p), tmp(p.get()) {}
michael@0: 
michael@0:     RefPtr<T>& refPtr;
michael@0:     T* tmp;
michael@0: 
michael@0:     OutParamRef() MOZ_DELETE;
michael@0:     OutParamRef& operator=(const OutParamRef&) MOZ_DELETE;
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * byRef cooperates with OutParamRef to implement COM outparam semantics.
michael@0:  */
michael@0: template<typename T>
michael@0: OutParamRef<T>
michael@0: byRef(RefPtr<T>& ptr)
michael@0: {
michael@0:   return OutParamRef<T>(ptr);
michael@0: }
michael@0: 
michael@0: } // namespace mozilla
michael@0: 
michael@0: #if 0
michael@0: 
michael@0: // Command line that builds these tests
michael@0: //
michael@0: //   cp RefPtr.h test.cc && g++ -g -Wall -pedantic -DDEBUG -o test test.cc && ./test
michael@0: 
michael@0: using namespace mozilla;
michael@0: 
michael@0: struct Foo : public RefCounted<Foo>
michael@0: {
michael@0:   MOZ_DECLARE_REFCOUNTED_TYPENAME(Foo)
michael@0:   Foo() : dead(false) { }
michael@0:   ~Foo() {
michael@0:     MOZ_ASSERT(!dead);
michael@0:     dead = true;
michael@0:     numDestroyed++;
michael@0:   }
michael@0: 
michael@0:   bool dead;
michael@0:   static int numDestroyed;
michael@0: };
michael@0: int Foo::numDestroyed;
michael@0: 
michael@0: struct Bar : public Foo { };
michael@0: 
michael@0: TemporaryRef<Foo>
michael@0: NewFoo()
michael@0: {
michael@0:   return RefPtr<Foo>(new Foo());
michael@0: }
michael@0: 
michael@0: TemporaryRef<Foo>
michael@0: NewBar()
michael@0: {
michael@0:   return new Bar();
michael@0: }
michael@0: 
michael@0: void
michael@0: GetNewFoo(Foo** f)
michael@0: {
michael@0:   *f = new Bar();
michael@0:   // Kids, don't try this at home
michael@0:   (*f)->AddRef();
michael@0: }
michael@0: 
michael@0: void
michael@0: GetPassedFoo(Foo** f)
michael@0: {
michael@0:   // Kids, don't try this at home
michael@0:   (*f)->AddRef();
michael@0: }
michael@0: 
michael@0: void
michael@0: GetNewFoo(RefPtr<Foo>* f)
michael@0: {
michael@0:   *f = new Bar();
michael@0: }
michael@0: 
michael@0: void
michael@0: GetPassedFoo(RefPtr<Foo>* f)
michael@0: {}
michael@0: 
michael@0: TemporaryRef<Foo>
michael@0: GetNullFoo()
michael@0: {
michael@0:   return 0;
michael@0: }
michael@0: 
michael@0: int
michael@0: main(int argc, char** argv)
michael@0: {
michael@0:   // This should blow up
michael@0: //    Foo* f = new Foo(); delete f;
michael@0: 
michael@0:   MOZ_ASSERT(0 == Foo::numDestroyed);
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     MOZ_ASSERT(f->refCount() == 1);
michael@0:   }
michael@0:   MOZ_ASSERT(1 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f1 = NewFoo();
michael@0:     RefPtr<Foo> f2(NewFoo());
michael@0:     MOZ_ASSERT(1 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(3 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> b = NewBar();
michael@0:     MOZ_ASSERT(3 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(4 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f1;
michael@0:     {
michael@0:       f1 = new Foo();
michael@0:       RefPtr<Foo> f2(f1);
michael@0:       RefPtr<Foo> f3 = f2;
michael@0:       MOZ_ASSERT(4 == Foo::numDestroyed);
michael@0:     }
michael@0:     MOZ_ASSERT(4 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(5 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     f.forget();
michael@0:     MOZ_ASSERT(6 == Foo::numDestroyed);
michael@0:   }
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     GetNewFoo(byRef(f));
michael@0:     MOZ_ASSERT(7 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(8 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     GetPassedFoo(byRef(f));
michael@0:     MOZ_ASSERT(8 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(9 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     GetNewFoo(&f);
michael@0:     MOZ_ASSERT(10 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(11 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = new Foo();
michael@0:     GetPassedFoo(&f);
michael@0:     MOZ_ASSERT(11 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(12 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f1 = new Bar();
michael@0:   }
michael@0:   MOZ_ASSERT(13 == Foo::numDestroyed);
michael@0: 
michael@0:   {
michael@0:     RefPtr<Foo> f = GetNullFoo();
michael@0:     MOZ_ASSERT(13 == Foo::numDestroyed);
michael@0:   }
michael@0:   MOZ_ASSERT(13 == Foo::numDestroyed);
michael@0: 
michael@0:   return 0;
michael@0: }
michael@0: 
michael@0: #endif
michael@0: 
michael@0: #endif /* mozilla_RefPtr_h */