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/*
* Copyright 2009, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
// An intrusive weak pointer implementation.
#ifndef O3D_CORE_CROSS_WEAK_PTR_H_
#define O3D_CORE_CROSS_WEAK_PTR_H_
#include "base/logging.h"
#include "core/cross/smart_ptr.h"
namespace o3d {
// A WeakPointer is a pointer that could go NULL if the object it is pointing
// to is freed/destroyed/released. That means every time you want to access the
// think the WeakPointer is pointing to you must call Get() and check for NULL.
//
// To use this WeakPointer, first, in the class you want it to point to add a
// WeakPointerManager field and initialize it in your constructor. Then provide
// a function GetWeakPointer() to get a WeakPointer to your class. Example.
//
// class MyClass {
// public:
// typedef WeakPointer<MyClass> WeakPointerType;
//
// MyClass() : weak_pointer_manager_(this) {
// }
//
// WeakPointerType GetWeakPointer() const {
// weak_pointer_manager_.GetWeakPointer();
// }
//
// private:
// WeakPointerType::WeakPointerManager weak_pointer_manager_;
// };
template <class C>
class WeakPointer {
public:
typedef C* Pointer;
typedef C& Reference;
typedef C ClassType;
WeakPointer() : handle_(typename WeakPointerHandle::Ref(NULL)) {
}
// This copy constructor is not marked explicit on purpose, so that
// we can copy weak pointers implicitly.
WeakPointer(const WeakPointer<C>& source) // NOLINT
: handle_(source.handle_) {
}
WeakPointer<C>& operator=(const WeakPointer<C>& rhs) {
if (this != &rhs) {
handle_ = rhs.handle_;
}
return *this;
}
// Gets the object this weak pointer is pointing to.
Pointer Get() const {
return handle_.IsNull() ? NULL : handle_->GetRaw();
}
// This class manages a WeakPointer for the object the WeakPointer is pointing
// to. If you forget to call Init you'll get an assert on destruction. It also
// enforces calling Reset on the weak pointer handle at destruction.
class WeakPointerManager {
public:
typedef C* Pointer;
typedef C& Reference;
typedef C ClassType;
typedef WeakPointer<C> WeakPointerType;
typedef typename WeakPointerType::WeakPointerHandle HandleType;
explicit WeakPointerManager(Pointer data)
: handle_(typename HandleType::Ref(new HandleType(data))) {
}
~WeakPointerManager() {
handle_->Reset();
}
WeakPointerType GetWeakPointer() const {
return handle_->GetWeakPointer();
}
private:
typename HandleType::Ref handle_;
};
private:
// This class holds the pointer to the actual object all weak pointers
// are pointing to. It is ref counted so when the last weak pointer
// goes away this handle will go away.
class WeakPointerHandle : public RefCounted {
public:
typedef SmartPointer<WeakPointerHandle> Ref;
explicit WeakPointerHandle(Pointer data)
: data_(data) {
}
void Reset() {
data_ = NULL;
}
Pointer GetRaw() const {
return data_;
}
WeakPointer<C> GetWeakPointer() const {
return WeakPointer<C>(this);
}
private:
Pointer data_;
DISALLOW_COPY_AND_ASSIGN(WeakPointerHandle);
};
explicit WeakPointer(const WeakPointerHandle* handle)
: handle_(typename WeakPointerHandle::Ref(
const_cast<WeakPointerHandle*>(handle))) {
}
typename WeakPointerHandle::Ref handle_;
};
// Provide a convenience equality test operator on SmartPointer objects.
template <class C>
inline bool operator==(const WeakPointer<C>& lhs, const WeakPointer<C>& rhs) {
return lhs.Get() == rhs.Get();
}
} // namespace o3d
#endif // O3D_CORE_CROSS_WEAK_PTR_H_
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