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Diffstat (limited to 'core/fxcrt/shared_copy_on_write.h')
-rw-r--r-- | core/fxcrt/shared_copy_on_write.h | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/core/fxcrt/shared_copy_on_write.h b/core/fxcrt/shared_copy_on_write.h new file mode 100644 index 0000000000..c04730d5e0 --- /dev/null +++ b/core/fxcrt/shared_copy_on_write.h @@ -0,0 +1,91 @@ +// 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_ |