/* Copyright 2021 The TensorFlow Authors. 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 XLA_TSL_PLATFORM_INTRUSIVE_PTR_H_
#define XLA_TSL_PLATFORM_INTRUSIVE_PTR_H_

#include <algorithm>
namespace tsl {
namespace core {

// A utility for managing the lifetime of ref-counted objects.
//
// Generally used for objects that derive from `tensorflow::RefCounted`.
template <class T>
class IntrusivePtr {
 public:
  // add_ref=false indicates that IntrusivePtr owns the underlying pointer.
  //
  // In most cases, we expect this to be called with add_ref=false, except in
  // special circumstances where the lifetime of the underlying RefCounted
  // object needs to be externally managed.
  IntrusivePtr(T* h, bool add_ref) { reset(h, add_ref); }
  IntrusivePtr(const IntrusivePtr& o) { reset(o.handle_, /*add_ref=*/true); }
  IntrusivePtr(IntrusivePtr&& o) noexcept { *this = std::move(o); }
  IntrusivePtr() {}
  void reset(T* h, bool add_ref) {
    if (h != handle_) {
      if (add_ref && h) h->Ref();
      if (handle_) handle_->Unref();
      handle_ = h;
    }
  }
  IntrusivePtr& operator=(const IntrusivePtr& o) {
    reset(o.handle_, /*add_ref=*/true);
    return *this;
  }
  IntrusivePtr& operator=(IntrusivePtr&& o) noexcept {
    if (handle_ != o.handle_) {
      // Must clear o.handle_ before calling reset to capture the case where
      // handle_->member == o. In this case, calling handle_->Unref first would
      // delete o.handle_ so we clear it out first.
      reset(o.detach(), /*add_ref=*/false);
    }
    return *this;
  }
  bool operator==(const IntrusivePtr& o) const { return handle_ == o.handle_; }
  T* operator->() const { return handle_; }
  T& operator*() const { return *handle_; }
  explicit operator bool() const noexcept { return get(); }
  T* get() const { return handle_; }
  // Releases ownership of the pointer without unreffing. Caller is responsible
  // for calling Unref on the returned pointer.
  T* detach() {
    T* handle = handle_;
    handle_ = nullptr;
    return handle;
  }

  ~IntrusivePtr() {
    if (handle_) handle_->Unref();
  }

 private:
  T* handle_ = nullptr;
};

}  // namespace core
}  // namespace tsl

#endif  // XLA_TSL_PLATFORM_INTRUSIVE_PTR_H_