1 files changed, 81 insertions, 0 deletions
diff --git a/core/fxcrt/cfx_count_ref.h b/core/fxcrt/cfx_count_ref.h
new file mode 100644
index 0000000000..3b9ccff8fe
--- /dev/null
+++ b/core/fxcrt/cfx_count_ref.h
@@ -0,0 +1,81 @@
+// 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_CFX_COUNT_REF_H_
+#define CORE_FXCRT_CFX_COUNT_REF_H_
+
+#include "core/fxcrt/cfx_retain_ptr.h"
+#include "core/fxcrt/fx_system.h"
+
+// A shared object with Copy on Write semantics that makes it appear as
+// if each one were independent.
+template <class ObjClass>
+class CFX_CountRef {
+ public:
+  CFX_CountRef() {}
+  CFX_CountRef(const CFX_CountRef& other) : m_pObject(other.m_pObject) {}
+  ~CFX_CountRef() {}
+
+  template <typename... Args>
+  ObjClass* Emplace(Args... params) {
+    m_pObject.Reset(new CountedObj(params...));
+    return m_pObject.Get();
+  }
+
+  CFX_CountRef& operator=(const CFX_CountRef& 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 CFX_CountRef& that) const {
+    return m_pObject == that.m_pObject;
+  }
+  bool operator!=(const CFX_CountRef& that) const { return !(*this == that); }
+  explicit operator bool() const { return !!m_pObject; }
+
+ private:
+  class CountedObj : public ObjClass {
+   public:
+    template <typename... Args>
+    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;
+  };
+
+  CFX_RetainPtr<CountedObj> m_pObject;
+};
+
+#endif  // CORE_FXCRT_CFX_COUNT_REF_H_