diff -r 000000000000 -r 6474c204b198 mfbt/RefPtr.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/RefPtr.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,521 @@
+/* -*- 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 */