Move most of Ref's functionality in RefBase for reuse.

This will allow using the same logic for other kinds of smartpointers,
like NSRef<>

Bug: dawn:89
Change-Id: Idbe08208fdb38b236f52635bc913162e60baf0f0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/32160
Reviewed-by: Stephen White <senorblanco@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/common/BUILD.gn

@@ -169,6 +169,7 @@ if (is_win || is_linux || is_chromeos || is_mac || is_fuchsia || is_android) {
       "Math.h",
       "PlacementAllocated.h",
       "Platform.h",
+      "RefBase.h",
       "RefCounted.cpp",
       "RefCounted.h",
       "Result.cpp",

src/common/CMakeLists.txt

@@ -31,6 +31,7 @@ target_sources(dawn_common PRIVATE
     "Math.h"
     "PlacementAllocated.h"
     "Platform.h"
+    "RefBase.h"
     "RefCounted.cpp"
     "RefCounted.h"
     "Result.cpp"

src/common/RefBase.h

@@ -0,0 +1,189 @@
+// Copyright 2020 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef COMMON_REFBASE_H_
+#define COMMON_REFBASE_H_
+
+#include "common/Compiler.h"
+
+#include <type_traits>
+
+// A common class for various smart-pointers acting on referenceable/releasable pointer-like
+// objects. Logic for each specialization can be customized using a Traits type that looks
+// like the following:
+//
+//   struct {
+//      static constexpr T kNullValue = ...;
+//      static void Reference(T value) { ... }
+//      static void Release(T value) { ... }
+//   };
+//
+// RefBase supports
+template <typename T, typename Traits>
+class RefBase {
+  private:
+    static constexpr T kNullValue = Traits::kNullValue;
+
+  public:
+    // Default constructor and destructor.
+    RefBase() : mValue(kNullValue) {
+    }
+
+    ~RefBase() {
+        Release();
+        mValue = kNullValue;
+    }
+
+    // Constructors from nullptr.
+    constexpr RefBase(std::nullptr_t) : RefBase() {
+    }
+
+    RefBase<T, Traits>& operator=(std::nullptr_t) {
+        Release();
+        mValue = kNullValue;
+        return *this;
+    }
+
+    // Constructors from a value T.
+    RefBase(T value) : mValue(value) {
+        Reference();
+    }
+
+    RefBase<T, Traits>& operator=(const T& value) {
+        mValue = value;
+        Reference();
+        return *this;
+    }
+
+    // Constructors from a RefBase<T>
+    RefBase(const RefBase<T, Traits>& other) : mValue(other.mValue) {
+        Reference();
+    }
+
+    RefBase<T, Traits>& operator=(const RefBase<T, Traits>& other) {
+        if (&other != this) {
+            other.Reference();
+            Release();
+            mValue = other.mValue;
+        }
+
+        return *this;
+    }
+
+    RefBase(RefBase<T, Traits>&& other) {
+        mValue = other.mValue;
+        other.mValue = kNullValue;
+    }
+
+    RefBase<T, Traits>& operator=(RefBase<T, Traits>&& other) {
+        if (&other != this) {
+            Release();
+            mValue = other.mValue;
+            other.mValue = kNullValue;
+        }
+
+        return *this;
+    }
+
+    // Constructors from a RefBase<U>. Note that in the *-assignment operators this cannot be the
+    // same as `other` because overload resolution rules would have chosen the *-assignement
+    // operators defined with `other` == RefBase<T, Traits>.
+    template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
+    RefBase(const RefBase<U, UTraits>& other) : mValue(other.mValue) {
+        Reference();
+    }
+
+    template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
+    RefBase<T, Traits>& operator=(const RefBase<U, UTraits>& other) {
+        other.Reference();
+        Release();
+        mValue = other.mValue;
+        return *this;
+    }
+
+    template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
+    RefBase(RefBase<U, UTraits>&& other) {
+        mValue = other.Detach();
+    }
+
+    template <typename U, typename UTraits, typename = typename std::is_convertible<U, T>::type>
+    RefBase<T, Traits>& operator=(RefBase<U, UTraits>&& other) {
+        Release();
+        mValue = other.Detach();
+        return *this;
+    }
+
+    // Comparison operators.
+    bool operator==(const T& other) const {
+        return mValue == other;
+    }
+
+    bool operator!=(const T& other) const {
+        return mValue != other;
+    }
+
+    operator bool() {
+        return mValue != kNullValue;
+    }
+
+    // Operator * and -> to act like a pointer.
+    const typename Traits::PointedType& operator*() const {
+        return *mValue;
+    }
+    typename Traits::PointedType& operator*() {
+        return *mValue;
+    }
+
+    const T operator->() const {
+        return mValue;
+    }
+    T operator->() {
+        return mValue;
+    }
+
+    // Smart pointer methods.
+    const T& Get() const {
+        return mValue;
+    }
+    T& Get() {
+        return mValue;
+    }
+
+    T Detach() DAWN_NO_DISCARD {
+        T value = mValue;
+        mValue = kNullValue;
+        return value;
+    }
+
+  private:
+    // Friend is needed so that instances of RefBase<U> can call Reference and Release on
+    // RefBase<T>.
+    template <typename U, typename UTraits>
+    friend class RefBase;
+
+    void Reference() const {
+        if (mValue != kNullValue) {
+            Traits::Reference(mValue);
+        }
+    }
+    void Release() const {
+        if (mValue != kNullValue) {
+            Traits::Release(mValue);
+        }
+    }
+
+    T mValue;
+};
+
+#endif  // COMMON_REFBASE_H_

src/common/RefCounted.h

@@ -15,6 +15,8 @@
 #ifndef COMMON_REFCOUNTED_H_
 #define COMMON_REFCOUNTED_H_
 
+#include "common/RefBase.h"
+
 #include <atomic>
 #include <cstdint>
 
@@ -39,146 +41,21 @@ class RefCounted {
 };
 
 template <typename T>
-class Ref {
+struct RefCountedTraits {
+    using PointedType = T;
+    static constexpr T* kNullValue = nullptr;
+    static void Reference(T* value) {
+        value->Reference();
+    }
+    static void Release(T* value) {
+        value->Release();
+    }
+};
+
+template <typename T>
+class Ref : public RefBase<T*, RefCountedTraits<T>> {
   public:
-    Ref() = default;
-
-    constexpr Ref(std::nullptr_t) {
-    }
-
-    Ref& operator=(std::nullptr_t) {
-        Release();
-        mPointee = nullptr;
-        return *this;
-    }
-
-    template <typename U>
-    Ref(U* p) : mPointee(p) {
-        static_assert(std::is_convertible<U*, T*>::value, "");
-        Reference();
-    }
-
-    Ref(const Ref<T>& other) : mPointee(other.mPointee) {
-        Reference();
-    }
-    template <typename U>
-    Ref(const Ref<U>& other) : mPointee(other.mPointee) {
-        static_assert(std::is_convertible<U*, T*>::value, "");
-        Reference();
-    }
-
-    Ref<T>& operator=(const Ref<T>& other) {
-        if (&other == this)
-            return *this;
-
-        other.Reference();
-        Release();
-        mPointee = other.mPointee;
-
-        return *this;
-    }
-
-    template <typename U>
-    Ref<T>& operator=(const Ref<U>& other) {
-        static_assert(std::is_convertible<U*, T*>::value, "");
-
-        other.Reference();
-        Release();
-        mPointee = other.mPointee;
-
-        return *this;
-    }
-
-    template <typename U>
-    Ref(Ref<U>&& other) {
-        static_assert(std::is_convertible<U*, T*>::value, "");
-        mPointee = other.mPointee;
-        other.mPointee = nullptr;
-    }
-
-    Ref<T>& operator=(Ref<T>&& other) {
-        if (&other == this)
-            return *this;
-
-        Release();
-        mPointee = other.mPointee;
-        other.mPointee = nullptr;
-
-        return *this;
-    }
-    template <typename U>
-    Ref<T>& operator=(Ref<U>&& other) {
-        static_assert(std::is_convertible<U*, T*>::value, "");
-
-        Release();
-        mPointee = other.mPointee;
-        other.mPointee = nullptr;
-
-        return *this;
-    }
-
-    ~Ref() {
-        Release();
-        mPointee = nullptr;
-    }
-
-    bool operator==(const T* other) const {
-        return mPointee == other;
-    }
-
-    bool operator!=(const T* other) const {
-        return mPointee != other;
-    }
-
-    operator bool() {
-        return mPointee != nullptr;
-    }
-
-    const T& operator*() const {
-        return *mPointee;
-    }
-    T& operator*() {
-        return *mPointee;
-    }
-
-    const T* operator->() const {
-        return mPointee;
-    }
-    T* operator->() {
-        return mPointee;
-    }
-
-    const T* Get() const {
-        return mPointee;
-    }
-    T* Get() {
-        return mPointee;
-    }
-
-    T* Detach() {
-        T* pointee = mPointee;
-        mPointee = nullptr;
-        return pointee;
-    }
-
-  private:
-    // Friend is needed so that instances of Ref<U> can assign mPointee
-    // members of Ref<T>.
-    template <typename U>
-    friend class Ref;
-
-    void Reference() const {
-        if (mPointee != nullptr) {
-            mPointee->Reference();
-        }
-    }
-    void Release() const {
-        if (mPointee != nullptr) {
-            mPointee->Release();
-        }
-    }
-
-    T* mPointee = nullptr;
+    using RefBase<T*, RefCountedTraits<T>>::RefBase;
 };
 
 template <typename T>

src/dawn_native/vulkan/TextureVk.cpp

@@ -483,7 +483,7 @@ namespace dawn_native { namespace vulkan {
         Ref<Texture> texture =
             AcquireRef(new Texture(device, descriptor, TextureState::OwnedExternal));
         texture->InitializeForSwapChain(nativeImage);
-        return std::move(texture);
+        return texture;
     }
 
     MaybeError Texture::InitializeAsInternalTexture(VkImageUsageFlags extraUsages) {

src/tests/unittests/RefCountedTests.cpp

@@ -43,14 +43,7 @@ class RCTest : public RefCounted {
 };
 
 struct RCTestDerived : public RCTest {
-    RCTestDerived() : RCTest() {
-    }
-
-    RCTestDerived(uint64_t payload) : RCTest(payload) {
-    }
-
-    RCTestDerived(bool* deleted) : RCTest(deleted) {
-    }
+    using RCTest::RCTest;
 };
 
 // Test that RCs start with one ref, and removing it destroys the object.