any_ptr.h

/* Copyright 2016 Google Inc. All Rights Reserved.
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
    http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/
 
#ifndef TENSORFLOW_SERVING_UTIL_ANY_PTR_H_
#define TENSORFLOW_SERVING_UTIL_ANY_PTR_H_
 
#include <cstddef>
#include <memory>
 
namespace tensorflow {
namespace serving {
 
class AnyPtr {
 public:
  AnyPtr() : type_id_(FastTypeId<void>()), ptr_(nullptr) {}
 
  AnyPtr(std::nullptr_t) : AnyPtr() {}  // NOLINT
 
  template <typename T>
  AnyPtr(T* ptr)  // NOLINT
      : type_id_(FastTypeId<T>()),
        // We need a double cast here, first to drop the type, and second to
        // drop constness. We always cast back to the appropriate type and
        // constness in get<>(), since FastTypeId is different for a const and
        // non-const T.
        ptr_(const_cast<void*>(reinterpret_cast<const void*>(ptr))) {}
 
  template <typename T>
  T* get() const {
    if (type_id_ != FastTypeId<T>()) {
      return nullptr;
    }
    return reinterpret_cast<T*>(ptr_);
  }
 
 private:
  template <typename Type>
  static size_t FastTypeId() {
    // Use a static variable to get a unique per-type address.
    static int dummy;
    return reinterpret_cast<std::size_t>(&dummy);
  }
 
  // The code for the type of 'ptr_'.
  std::size_t type_id_;
 
  // The underlying pointer.
  void* ptr_;
};
 
class UniqueAnyPtr {
 public:
  UniqueAnyPtr() = default;
  UniqueAnyPtr(std::nullptr_t) : UniqueAnyPtr() {}  // NOLINT
 
  template <typename T>
  explicit UniqueAnyPtr(std::unique_ptr<T> ptr)
      : ptr_(ptr.release()), deleter_(DeleterForType<T>()) {}
 
  ~UniqueAnyPtr() { deleter_(ptr_); }
 
  // Disable copy.
  UniqueAnyPtr(const UniqueAnyPtr& other) = delete;
  UniqueAnyPtr& operator=(const UniqueAnyPtr& other) = delete;
 
  // Allow move.
  UniqueAnyPtr(UniqueAnyPtr&& other) { swap(other); }
 
  UniqueAnyPtr& operator=(UniqueAnyPtr&& other) {
    swap(other);
    return *this;
  }
 
  template <typename T>
  T* get() const {
    return ptr_.get<T>();
  }
 
  const AnyPtr& as_any_ptr() const { return ptr_; }
 
  void swap(UniqueAnyPtr& other) {
    using ::std::swap;
    swap(ptr_, other.ptr_);
    swap(deleter_, other.deleter_);
  }
 
 private:
  // We use a raw function pointer. This eliminates the copy and calling
  // overhead of std::function.
  using Deleter = void (*)(AnyPtr ptr);
 
  // Returns a 'Deleter' that will delete it's argument as an instance of 'T'.
  // Always returns the same value for the same 'T'.
  template <typename T>
  static Deleter DeleterForType() {
    return [](AnyPtr ptr) { delete ptr.get<T>(); };
  }
 
  static Deleter NoOpDeleter() {
    return [](AnyPtr ptr) {};
  }
 
  AnyPtr ptr_ = nullptr;
  Deleter deleter_ = NoOpDeleter();
};
 
}  // namespace serving
}  // namespace tensorflow
 
#endif  // TENSORFLOW_SERVING_UTIL_ANY_PTR_H_