The Tor Browser: comparison mfbt/RefPtr.h

--1:000000000000
+:e7fafcb94df2
+/* -*- 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 */

The Tor Browser / file comparison

comparison: mfbt/RefPtr.h

mfbt/RefPtr.h