Issue 4125 - [emscripten] Convert filter classes to C++

compiled/intrusive_ptr.h

+// Parts of this code have been copied from boost/smart_ptr/intrusive_ptr.hpp.
+//
+//  Copyright (c) 2001, 2002 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef ADBLOCK_PLUS_INTRUSIVE_PTR_H
+#define ADBLOCK_PLUS_INTRUSIVE_PTR_H
+
+#include <type_traits>
+
+class ref_counted
+{
+public:
+  void AddRef()
+  {
+    mRefCount++;
+  }
+
+  void ReleaseRef()
+  {
+    if (--mRefCount == 0)

[René Jeschke, 2016/02/02 11:11:23]

Nit: having a check on `0` here feels wrong and may lead to unwanted behaviour
if one tries to release a `0` ref. I suggest using `--mRefCount <= 0`.

[Wladimir Palant, 2016/02/02 17:55:19]

It's quite the opposite I think - if we are already in the destructor (mRefCount
is 0) and somebody releases the ref again by mistake we won't delete a second
time. Either way, ref count dropping below 0 is always a bug - not sure whether
we can do anything sane in that case, other than crashing maybe.

+      delete this;
+  }
+
+protected:
+  ref_counted()
+      : mRefCount(0)
+  {
+  }
+
+  // We need this virtual destructor, otherwise pointers to ref_counted and
+  // pointers to derived classes won't have the same value (e.g. converting from
+  // Filter* to ref_counted* decreases pointer value by 4).
+  virtual ~ref_counted()
+  {
+  }
+
+private:
+  int mRefCount;
+};
+
+template<class T,
+    class = typename std::enable_if<std::is_base_of<ref_counted,T>::value>::type>
+class intrusive_ptr
+{
+public:
+  intrusive_ptr()
+      : mPointer(nullptr)
+  {
+  }
+
+  intrusive_ptr(T* pointer)
+      : mPointer(pointer)
+  {
+    if (mPointer)
+      mPointer->AddRef();
+  }
+
+  intrusive_ptr(const intrusive_ptr& other)
+      : mPointer(other.mPointer)
+  {
+    if (mPointer)
+      mPointer->AddRef();
+  }
+
+  intrusive_ptr(intrusive_ptr&& other)
+      : mPointer(other.mPointer)
+  {
+    other.mPointer = nullptr;
+  }
+
+  ~intrusive_ptr()
+  {
+    if (mPointer)
+      mPointer->ReleaseRef();
+  }
+
+  intrusive_ptr& operator=(intrusive_ptr& other)
+  {
+    intrusive_ptr(other).swap(*this);
+    return *this;
+  }
+
+  intrusive_ptr& operator=(intrusive_ptr&& other)
+  {
+    intrusive_ptr(other).swap(*this);
+    return *this;
+  }
+
+  intrusive_ptr& operator=(T* other)
+  {
+    intrusive_ptr(other).swap(*this);
+  }
+
+  void reset()
+  {
+    intrusive_ptr().swap(*this);
+  }
+
+  void reset(T* other)
+  {
+    intrusive_ptr(other).swap(*this);
+  }
+
+  T* get() const
+  {
+    return mPointer;
+  }
+
+  T& operator*() const
+  {
+    return *mPointer;
+  }
+
+  T* operator->() const
+  {
+    return mPointer;
+  }
+
+  operator bool() const
+  {
+    return mPointer != nullptr;
+  }
+
+  operator T*() const
+  {
+    return mPointer;
+  }
+
+  bool operator!() const
+  {
+    return mPointer == nullptr;
+  }
+
+  void swap(intrusive_ptr& other)
+  {
+    T* tmp = mPointer;

[René Jeschke, 2016/02/02 11:11:24]

Nit: is there a specific reason why you're not using `std::swap` here?

[Wladimir Palant, 2016/02/02 17:55:19]

You have to ask Boost devs :)

I haven't heard about std::swap() before but I'll happily use it now.

+    mPointer = other.mPointer;
+    other.mPointer = tmp;
+  }
+
+private:
+  T* mPointer;
+};
+
+template<class T, class U>
+inline bool operator==(const intrusive_ptr<T>& a, const intrusive_ptr<U>& b)
+{
+  return a.get() == b.get();
+}
+
+template<class T, class U>
+inline bool operator!=(const intrusive_ptr<T>& a, const intrusive_ptr<U>& b)
+{
+  return a.get() != b.get();
+}
+
+template<class T, class U>
+inline bool operator==(const intrusive_ptr<T>& a, const U* b)
+{
+  return a.get() == b;
+}
+
+template<class T, class U>
+inline bool operator!=(const intrusive_ptr<T>& a, const U* b)
+{
+    return a.get() != b;
+}
+
+template<class T, class U>
+inline bool operator==(const T* a, const intrusive_ptr<U>& b)
+{
+  return a == b.get();
+}
+
+template<class T, class U>
+inline bool operator!=(const T* a, intrusive_ptr<U> const& b)
+{
+  return a != b.get();
+}
+
+#endif