Initial work

external/android-emugl/shared/emugl/common/smart_ptr.h

@@ -0,0 +1,150 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// 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 EMUGL_SMART_PTR_H
+#define EMUGL_SMART_PTR_H
+
+#include <stddef.h>
+
+namespace emugl {
+
+// Hidden atomic ref-counting implementation.
+class RefCount;
+
+// Base class for all templated SmartPtr<> instances. Reduces
+// template expansion and code. Consider this to be an implementation
+// detail of SmartPtr<>, so don't rely on anything here.
+class SmartPtrBase {
+public:
+    // Defrault constructor.
+    SmartPtrBase() : mPtr(NULL), mRefCount(NULL) {}
+
+    // Normal constructor. This takes ownership of |ptr|, though only
+    // template instances are capable of destroying the object.
+    explicit SmartPtrBase(void* ptr);
+
+    // Copy-constructor, this increments the reference count.
+    SmartPtrBase(const SmartPtrBase& other);
+
+    // Assignment operator, also increments the reference count.
+    SmartPtrBase& operator=(const SmartPtrBase& other);
+
+    // Nothing happens in this destructor, the real work must be performed
+    // in subclasses.
+    ~SmartPtrBase() {}
+
+
+    // Used to enable 'if (smart_ptr) { ... }' properly.
+    operator void*() const {
+        return mPtr;
+    }
+
+    // Return internal reference count value, only use for unit testing.
+    int getRefCount() const;
+
+protected:
+    // Used internally to increment the reference count.
+    void addRef();
+
+    // Copy the |other| into this instance, returns the old pointer value
+    // if it needs to be destroyed by the caller, or NULL otherwise.
+    void* copyFrom(const SmartPtrBase& other);
+
+    // Used internally to decrement the reference count, if it reaches 0,
+    // returns the pointer to be destroyed, NULL otherwise.
+    void* release();
+
+    void* mPtr;
+    RefCount* mRefCount;
+};
+
+
+// The real template class to be used for smart pointers.
+// Typical uses:
+//
+//     SmartPtr<Foo>  ptr(new Foo());   // takes ownership.
+//     SmartPtr<Foo>  ptr2;             // empty pointer.
+//     ptr2 = ptr;                      // copies pointer + increment reference count.
+//     Foo* obj = ptr.Ptr();            // access pointed object.
+//     ptr->DoStuff();                  // operate directly on pointed object.
+//     (*ptr)->DoStuff();               // same here.
+//
+// On scope exit, the internal reference count is decremented and the
+// object is deleted automatically when it reaches 0, indicating that
+// there are no more owners.
+//
+// IMPORTANT: You need to be sure that only one 'chain' of smart pointers
+// own a given object. I.e. the following is incorrect:
+//
+//     Foo* foo = new Foo();      // create new instance.
+//     SmartPtr<Foo>  ptr(foo);   // |ptr| takes ownership of |foo|.
+//     SmartPtr<Foo>  ptr2(foo);  // |ptr2| takes also ownership of |foo|.
+//
+// The problem is that |ptr| and |ptr2| don't know anything about each
+// other, and will not share the same reference count. Once a smart pointer
+// owns an object, only use other smart pointers that are copy-constructed
+// or assigned with the initial one to keep everything consistent.
+template <class T>
+class SmartPtr : public emugl::SmartPtrBase {
+public:
+    // Default constructor. The instance holds a NULL pointer.
+    SmartPtr() : SmartPtrBase() {}
+
+    // Regular constructor, takes ownership of |ptr|.
+    explicit SmartPtr(T* ptr) : SmartPtrBase(ptr) {}
+
+    // Copy-constructor, |this| and |other| will share the same internal
+    // reference count, which is incremented by 1.
+    SmartPtr(const SmartPtr& other)
+            : SmartPtrBase(reinterpret_cast<const SmartPtrBase&>(other)) {}
+
+    // Assignment operator, same semantics as copy-constructor.
+    SmartPtr& operator=(const SmartPtr& other) {
+      void* old_ptr = copyFrom(static_cast<const SmartPtrBase&>(other));
+      if (old_ptr)
+        delete reinterpret_cast<T*>(old_ptr);
+      return *this;
+    }
+
+    // Destructor, decrements reference count and destroys the object
+    // if it reaches 0 (indicating this was the last owning smart pointer).
+    ~SmartPtr() {
+        void* ptr = release();
+        if (ptr)
+          delete reinterpret_cast<T*>(ptr);
+    }
+
+    // Return owned object instance, or NULL.
+    T* Ptr() const {
+        return reinterpret_cast<T*>(mPtr);
+    }
+
+    // Return owned object instance, or NULL
+    const T* constPtr() const {
+        return reinterpret_cast<const T*>(mPtr);
+    }
+
+    // Operate directly on owned object.
+    T* operator->() const {
+        return Ptr();
+    }
+
+    // Return reference to owned object.
+    T& operator*() const {
+        return *Ptr();
+    }
+};
+
+}  // namespace emugl
+
+#endif // EMUGL_SMART_PTR_H