lock_guard_ptr.h

// Copyright (c) 2018 PaddlePaddle 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.

#pragma once
#include <stdint.h>
#include <memory>
#include <mutex>  // NOLINT
namespace paddle {
namespace platform {

/**
 * LockGuard for std::unique_ptr<LockType>. It will do nothing when guarded ptr
 * is nullptr.
 *
 * The advantage of using `LockGuardPtr` instead of
 * std::unique<std::lock_guard<lock_type>> is this type is totally a stack
 * variable. There is no heap allocation at all.
 */
template <typename LockType>
class LockGuardPtr {
 public:
  explicit LockGuardPtr(std::unique_ptr<LockType>& lock_ptr)  // NOLINT
      : lock_(lock_ptr.get()) {
    if (lock_) {
      lock_->lock();
    }
  }
  ~LockGuardPtr() {
    if (lock_) {
      lock_->unlock();
    }
  }

  LockGuardPtr(const LockGuardPtr&) = delete;
  LockGuardPtr& operator=(const LockGuardPtr&) = delete;
  LockGuardPtr(LockGuardPtr&&) = delete;
  LockGuardPtr& operator=(LockGuardPtr&&) = delete;

 private:
  LockType* lock_;
};

}  // namespace platform
}  // namespace paddle