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// Copyright 2016 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
#ifndef CORE_FXCRT_SHARED_COPY_ON_WRITE_H_
#define CORE_FXCRT_SHARED_COPY_ON_WRITE_H_
#include "core/fxcrt/fx_system.h"
#include "core/fxcrt/retain_ptr.h"
namespace fxcrt {
// A shared object with Copy on Write semantics that makes it appear as
// if each one were independent.
template <class ObjClass>
class SharedCopyOnWrite {
public:
SharedCopyOnWrite() {}
SharedCopyOnWrite(const SharedCopyOnWrite& other)
: m_pObject(other.m_pObject) {}
~SharedCopyOnWrite() {}
template <typename... Args>
ObjClass* Emplace(Args... params) {
m_pObject.Reset(new CountedObj(params...));
return m_pObject.Get();
}
SharedCopyOnWrite& operator=(const SharedCopyOnWrite& that) {
if (*this != that)
m_pObject = that.m_pObject;
return *this;
}
void SetNull() { m_pObject.Reset(); }
const ObjClass* GetObject() const { return m_pObject.Get(); }
template <typename... Args>
ObjClass* GetPrivateCopy(Args... params) {
if (!m_pObject)
return Emplace(params...);
if (!m_pObject->HasOneRef())
m_pObject.Reset(new CountedObj(*m_pObject));
return m_pObject.Get();
}
bool operator==(const SharedCopyOnWrite& that) const {
return m_pObject == that.m_pObject;
}
bool operator!=(const SharedCopyOnWrite& that) const {
return !(*this == that);
}
explicit operator bool() const { return !!m_pObject; }
private:
class CountedObj : public ObjClass {
public:
template <typename... Args>
// NOLINTNEXTLINE(runtime/explicit)
CountedObj(Args... params) : ObjClass(params...), m_RefCount(0) {}
CountedObj(const CountedObj& src) : ObjClass(src), m_RefCount(0) {}
~CountedObj() { m_RefCount = 0; }
bool HasOneRef() const { return m_RefCount == 1; }
void Retain() { m_RefCount++; }
void Release() {
ASSERT(m_RefCount);
if (--m_RefCount == 0)
delete this;
}
private:
// To ensure ref counts do not overflow, consider the worst possible case:
// the entire address space contains nothing but pointers to this object.
// Since the count increments with each new pointer, the largest value is
// the number of pointers that can fit into the address space. The size of
// the address space itself is a good upper bound on it.
intptr_t m_RefCount;
};
RetainPtr<CountedObj> m_pObject;
};
} // namespace fxcrt
using fxcrt::SharedCopyOnWrite;
#endif // CORE_FXCRT_SHARED_COPY_ON_WRITE_H_
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