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// 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
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