Bug 661973: Implement mozilla::RefCounted, RefPtr, TemporaryRef, OutParamRef, and byRef. r=Bas,luke sr=roc

js/src/Makefile.in

@@ -297,6 +297,7 @@ EXPORTS_NAMESPACES += mozilla
 
 EXPORTS_mozilla = \
 		RangedPtr.h \
+		RefPtr.h	\
 		Types.h		\
 		Util.h          \
 		$(NULL)

mfbt/RefPtr.h

@@ -0,0 +1,413 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sw=4 et tw=99 ft=cpp:
+ *
+ * ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at:
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla Code.
+ *
+ * The Initial Developer of the Original Code is
+ *   The Mozilla Foundation
+ * Portions created by the Initial Developer are Copyright (C) 2011
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *   Chris Jones <jones.chris.g@gmail.com>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+#ifndef mozilla_RefPtr_h_
+#define mozilla_RefPtr_h_
+
+#include "mozilla/Util.h"
+
+/**
+ * Helpers for defining and using refcounted objects.
+ */
+
+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==-0xdead.  This
+ * state distinguishes use-before-ref (refcount==0) from
+ * use-after-destroy (refcount==-0xdead).
+ */
+template<typename T>
+class RefCounted
+{
+    friend class RefPtr<T>;
+
+public:
+    RefCounted() : refCnt(0) { }
+    ~RefCounted() { MOZ_ASSERT(refCnt == -0xdead); }
+
+    // Compatibility with nsRefPtr.
+    void AddRef() {
+        MOZ_ASSERT(refCnt >= 0);
+        ++refCnt;
+    }
+
+    void Release() {
+        MOZ_ASSERT(refCnt > 0);
+        if (0 == --refCnt) {
+#ifdef DEBUG
+            refCnt = -0xdead;
+#endif
+            delete static_cast<T*>(this);
+        }
+    }
+
+    // Compatibility with wtf::RefPtr.
+    void ref() { AddRef(); }
+    void deref() { Release(); }
+    int refCount() const { return refCnt; }
+    bool hasOneRef() const {
+        MOZ_ASSERT(refCnt > 0);
+        return refCnt == 1;
+    }
+
+private:
+    int refCnt;
+};
+
+/**
+ * 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>;
+
+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);
+    }
+
+    T* get() const { return ptr; }
+    operator T*() const { return ptr; }
+    T* operator->() const { return ptr; }
+    T& operator*() const { return *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>;
+
+public:
+    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) : ptr(t) {}
+
+    mutable T* ptr;
+
+    TemporaryRef();
+    TemporaryRef& operator=(const TemporaryRef&);
+};
+
+/**
+ * OutParamRef is a wrapper that tracks a refcounted pointer passed as
+ * an outparam argument to a function.  If OutParamRef holds a ref to
+ * an object that's reassigned during a function call in which the
+ * OutParamRef is an outparam, then the old object is unref'd and the
+ * new object is ref'd.
+ *
+ * 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 = tmp; }
+
+    operator T**() { return &tmp; }
+
+private:
+    OutParamRef(RefPtr<T>& p) : refPtr(p), tmp(p.get()) {}
+
+    RefPtr<T>& refPtr;
+    T* tmp;
+
+    OutParamRef();
+    OutParamRef& operator=(const OutParamRef&);
+};
+
+template<typename T>
+OutParamRef<T>
+byRef(RefPtr<T>& ptr)
+{
+    return OutParamRef<T>(ptr);
+}
+
+} // namespace mozilla
+
+#endif // mozilla_RefPtr_h_
+
+
+#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>
+{
+    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()
+{
+    RefPtr<Foo> f = new Foo();
+    return f.forget();
+}
+
+TemporaryRef<Foo>
+NewBar()
+{
+    RefPtr<Bar> b = new Bar();
+    return b.forget();
+}
+
+void
+GetNewFoo(Foo** f)
+{
+    *f = new Bar();
+}
+
+void
+GetPassedFoo(Foo** f)
+{}
+
+void
+GetNewFoo(RefPtr<Foo>* f)
+{
+    *f = new Bar();
+}
+
+void
+GetPassedFoo(RefPtr<Foo>* f)
+{}
+
+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);
+
+    return 0;
+}
+
+#endif