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src/include/ref_counted.h

Index: src/include/ref_counted.h
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+// Copyright (c) 2010 The Native Client Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_
+#define NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_
+
+namespace nacl {
+
+namespace subtle {
+
+class RefCountedBase {
+ public:
+  static bool ImplementsThreadSafeReferenceCounting() { return false; }
+
+  bool HasOneRef() const { return ref_count_ == 1; }
+
+ protected:
+  RefCountedBase() : ref_count_(0) { }
+  ~RefCountedBase() { }
+
+  void AddRef() const { ++ref_count_; }
+
+  // Returns true if the object should self-delete.
+  bool Release() const { return --ref_count_ == 0; }
+
+ private:
+  mutable int ref_count_;
+
+  RefCountedBase(const RefCountedBase&);
+  void operator=(const RefCountedBase&);
+};
+
+}  // namespace subtle
+
+//
+// A base class for reference counted classes.  Otherwise, known as a cheap
+// knock-off of WebKit's RefCounted<T> class.  To use this guy just extend your
+// class from it like so:
+//
+//   class MyFoo : public nacl::RefCounted<MyFoo> {
+//    ...
+//    private:
+//     friend class nacl::RefCounted<MyFoo>;
+//     ~MyFoo();
+//   };
+//
+// You should always make your destructor private, to avoid any code deleting
+// the object accidently while there are references to it.
+template <class T>
+class RefCounted : public subtle::RefCountedBase {
+ public:
+  RefCounted() { }
+  ~RefCounted() { }
+
+  void AddRef() const {
+    subtle::RefCountedBase::AddRef();
+  }
+
+  void Release() const {
+    if (subtle::RefCountedBase::Release()) {
+      delete static_cast<const T*>(this);
+    }
+  }
+
+ private:
+  RefCounted(const RefCounted<T>&);
+  void operator=(const RefCounted<T>&);
+};
+
+//
+// A wrapper for some piece of data so we can place other things in
+// scoped_refptrs<>.
+//
+template<typename T>
+class RefCountedData : public nacl::RefCounted< nacl::RefCountedData<T> > {
+ public:
+  RefCountedData() : data() {}
+  RefCountedData(const T& in_value) : data(in_value) {}
+
+  T data;
+};
+
+}  // namespace nacl
+
+//
+// A smart pointer class for reference counted objects.  Use this class instead
+// of calling AddRef and Release manually on a reference counted object to
+// avoid common memory leaks caused by forgetting to Release an object
+// reference.  Sample usage:
+//
+//   class MyFoo : public RefCounted<MyFoo> {
+//    ...
+//   };
+//
+//   void some_function() {
+//     scoped_refptr<MyFoo> foo = new MyFoo();
+//     foo->Method(param);
+//     // |foo| is released when this function returns
+//   }
+//
+//   void some_other_function() {
+//     scoped_refptr<MyFoo> foo = new MyFoo();
+//     ...
+//     foo = NULL;  // explicitly releases |foo|
+//     ...
+//     if (foo)
+//       foo->Method(param);
+//   }
+//
+// The above examples show how scoped_refptr<T> acts like a pointer to T.
+// Given two scoped_refptr<T> classes, it is also possible to exchange
+// references between the two objects, like so:
+//
+//   {
+//     scoped_refptr<MyFoo> a = new MyFoo();
+//     scoped_refptr<MyFoo> b;
+//
+//     b.swap(a);
+//     // now, |b| references the MyFoo object, and |a| references NULL.
+//   }
+//
+// To make both |a| and |b| in the above example reference the same MyFoo
+// object, simply use the assignment operator:
+//
+//   {
+//     scoped_refptr<MyFoo> a = new MyFoo();
+//     scoped_refptr<MyFoo> b;
+//
+//     b = a;
+//     // now, |a| and |b| each own a reference to the same MyFoo object.
+//   }
+//
+template <class T>
+class scoped_refptr {
+ public:
+  scoped_refptr() : ptr_((T*)0) {
+  }
+
+  scoped_refptr(T* p) : ptr_(p) {
+    if (ptr_)
+      ptr_->AddRef();
+  }
+
+  scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
+    if (ptr_)
+      ptr_->AddRef();
+  }
+
+  template <typename U>
+  scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
+    if (ptr_)
+      ptr_->AddRef();
+  }
+
+  ~scoped_refptr() {
+    if (ptr_)
+      ptr_->Release();
+  }
+
+  T* get() const { return ptr_; }
+  operator T*() const { return ptr_; }
+  T* operator->() const { return ptr_; }
+
+  // Release a pointer.
+  // The return value is the current pointer held by this object.
+  // If this object holds a NULL pointer, the return value is NULL.
+  // After this operation, this object will hold a NULL pointer,
+  // and will not own the object any more.
+  T* release() {
+    T* retVal = ptr_;
+    ptr_ = (void*)0;
+    return retVal;
+  }
+
+  scoped_refptr<T>& operator=(T* p) {
+    // AddRef first so that self assignment should work
+    if (p)
+      p->AddRef();
+    if (ptr_ )
+      ptr_ ->Release();
+    ptr_ = p;
+    return *this;
+  }
+
+  scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
+    return *this = r.ptr_;
+  }
+
+  template <typename U>
+  scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
+    return *this = r.get();
+  }
+
+  void swap(T** pp) {
+    T* p = ptr_;
+    ptr_ = *pp;
+    *pp = p;
+  }
+
+  void swap(scoped_refptr<T>& r) {
+    swap(&r.ptr_);
+  }
+
+ protected:
+  T* ptr_;
+};
+
+// Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
+// having to retype all the template arguments
+template <typename T>
+scoped_refptr<T> make_scoped_refptr(T* t) {
+  return scoped_refptr<T>(t);
+}
+
+#endif  // NATIVE_CLIENT_SRC_INCLUDE_REF_COUNTED_H_
+