EDK: Move ref counting classes to mojo/edk/util.

mojo/edk/system/ref_counted.h

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Provides a base class for reference-counted classes.
-
-#ifndef MOJO_EDK_SYSTEM_REF_COUNTED_H_
-#define MOJO_EDK_SYSTEM_REF_COUNTED_H_
-
-#include <assert.h>
-
-#include <cstddef>
-#include <utility>
-
-#include "mojo/edk/system/ref_counted_internal.h"
-#include "mojo/edk/system/ref_ptr.h"
-#include "mojo/public/cpp/system/macros.h"
-
-namespace mojo {
-namespace system {
-
-// A base class for (thread-safe) reference-counted classes. Use like:
-//
-//   class Foo : public RefCountedThreadSafe<Foo> {
-//     ...
-//   };
-//
-// |~Foo()| *may* be made private (e.g., to avoid accidental deletion of objects
-// while there are still references to them), |Foo| should friend
-// |RefCountedThreadSafe<Foo>|; use |FRIEND_REF_COUNTED_THREAD_SAFE()| for this:
-//
-//   class Foo : public RefCountedThreadSafe<Foo> {
-//     ...
-//    private:
-//     FRIEND_REF_COUNTED_THREAD_SAFE(Foo);
-//     ~Foo();
-//     ...
-//   };
-//
-// Similarly, |Foo(...)| may be made private. In this case, there should either
-// be a static factory method performing the requisite adoption:
-//
-//   class Foo : public RefCountedThreadSafe<Foo> {
-//     ...
-//    public:
-//     inline static RefPtr<Foo> Create() { return AdoptRef(new Foo()); }
-//     ...
-//    private:
-//     Foo();
-//     ...
-//   };
-//
-// Or, to allow |MakeRefCounted()| to be used, use |FRIEND_MAKE_REF_COUNTED()|:
-//
-//   class Foo : public RefCountedThreadSafe<Foo> {
-//     ...
-//    private:
-//     FRIEND_MAKE_REF_COUNTED(Foo);
-//     Foo();
-//     Foo(const Bar& bar, bool maybe);
-//     ...
-//   };
-//
-// For now, we only have thread-safe reference counting, since that's all we
-// need. It's easy enough to add thread-unsafe versions if necessary.
-template <typename T>
-class RefCountedThreadSafe : public internal::RefCountedThreadSafeBase {
- public:
-  // Adds a reference to this object.
-  // Inherited from the internal superclass:
-  //   void AddRef() const;
-
-  // Releases a reference to this object. This will destroy this object once the
-  // last reference is released.
-  void Release() const {
-    if (internal::RefCountedThreadSafeBase::Release())
-      delete static_cast<const T*>(this);
-  }
-
-  // Asserts that there is exactly one reference to this object; does nothing in
-  // Release builds (when |NDEBUG| is defined).
-  // Inherited from the internal superclass:
-  //   void AssertHasOneRef();
-
- protected:
-  // Constructor. Note that the object is constructed with a reference count of
-  // 1, and then must be adopted (see |AdoptRef()| in ref_ptr.h).
-  RefCountedThreadSafe() {}
-
-  // Destructor. Note that this object should only be destroyed via |Release()|
-  // (see above), or something that calls |Release()| (see, e.g., |RefPtr<>| in
-  // ref_ptr.h).
-  ~RefCountedThreadSafe() {}
-
- private:
-#ifndef NDEBUG
-  template <typename U>
-  friend RefPtr<U> AdoptRef(U*);
-  // Marks the initial reference (assumed on construction) as adopted. This is
-  // only required for Debug builds (when |NDEBUG| is not defined).
-  // TODO(vtl): Should this really be private? This makes manual ref-counting
-  // and also writing one's own ref pointer class impossible.
-  void Adopt() { internal::RefCountedThreadSafeBase::Adopt(); }
-#endif
-
-  MOJO_DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafe);
-};
-
-// If you subclass |RefCountedThreadSafe| and want to keep your destructor
-// private, use this. (See the example above |RefCountedThreadSafe|.)
-#define FRIEND_REF_COUNTED_THREAD_SAFE(T) \
-  friend class ::mojo::system::RefCountedThreadSafe<T>
-
-// If you want to keep your constructor(s) private and still want to use
-// |MakeRefCounted<T>()|, use this. (See the example above
-// |RefCountedThreadSafe|.)
-#define FRIEND_MAKE_REF_COUNTED(T) \
-  friend class ::mojo::system::internal::MakeRefCountedHelper<T>
-
-}  // namespace system
-}  // namespace mojo
-
-#endif  // MOJO_EDK_SYSTEM_REF_COUNTED_H_