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

mojo/edk/system/ref_counted_internal.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.
-
-// Internal implementation details for ref_counted.h.
-
-#ifndef MOJO_EDK_SYSTEM_REF_COUNTED_INTERNAL_H_
-#define MOJO_EDK_SYSTEM_REF_COUNTED_INTERNAL_H_
-
-#include <assert.h>
-
-#include <atomic>
-
-#include "mojo/public/cpp/system/macros.h"
-
-namespace mojo {
-namespace system {
-namespace internal {
-
-class RefCountedThreadSafeBase {
- public:
-  void AddRef() const {
-    assert(!adoption_required_);
-    assert(!destruction_started_);
-    ref_count_.fetch_add(1u, std::memory_order_relaxed);
-  }
-
-  void AssertHasOneRef() const {
-    assert(ref_count_.load(std::memory_order_acquire) == 1u);
-  }
-
- protected:
-  RefCountedThreadSafeBase();
-  ~RefCountedThreadSafeBase();
-
-  // Returns true if the object should self-delete.
-  bool Release() const {
-    assert(!adoption_required_);
-    assert(!destruction_started_);
-    assert(ref_count_.load(std::memory_order_acquire) != 0u);
-    // TODO(vtl): We could add the following:
-    //     if (ref_count_.load(std::memory_order_relaxed) == 1u) {
-    // #ifndef NDEBUG
-    //       destruction_started_= true;
-    // #endif
-    //       return true;
-    //     }
-    // This would be correct. On ARM (an Nexus 4), in *single-threaded* tests,
-    // this seems to make the destruction case marginally faster (barely
-    // measurable), and while the non-destruction case remains about the same
-    // (possibly marginally slower, but my measurements aren't good enough to
-    // have any confidence in that). I should try multithreaded/multicore tests.
-    if (ref_count_.fetch_sub(1u, std::memory_order_release) == 1u) {
-      std::atomic_thread_fence(std::memory_order_acquire);
-#ifndef NDEBUG
-      destruction_started_ = true;
-#endif
-      return true;
-    }
-    return false;
-  }
-
-#ifndef NDEBUG
-  void Adopt() {
-    assert(adoption_required_);
-    adoption_required_ = false;
-  }
-#endif
-
- private:
-  mutable std::atomic_uint_fast32_t ref_count_;
-
-#ifndef NDEBUG
-  mutable bool adoption_required_;
-  mutable bool destruction_started_;
-#endif
-
-  MOJO_DISALLOW_COPY_AND_ASSIGN(RefCountedThreadSafeBase);
-};
-
-inline RefCountedThreadSafeBase::RefCountedThreadSafeBase()
-    : ref_count_(1u)
-#ifndef NDEBUG
-      ,
-      adoption_required_(true),
-      destruction_started_(false)
-#endif
-{
-}
-
-inline RefCountedThreadSafeBase::~RefCountedThreadSafeBase() {
-  assert(!adoption_required_);
-  // Should only be destroyed as a result of |Release()|.
-  assert(destruction_started_);
-}
-
-}  // namespace internal
-}  // namespace system
-}  // namespace mojo
-
-#endif  // MOJO_EDK_SYSTEM_REF_COUNTED_INTERNAL_H_