loaned_message.hpp

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// Copyright 2019 Open Source Robotics Foundation, Inc.
//
// 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 RCLCPP__LOANED_MESSAGE_HPP_
#define RCLCPP__LOANED_MESSAGE_HPP_

#include <memory>
#include <utility>

#include "rclcpp/allocator/allocator_common.hpp"
#include "rclcpp/logging.hpp"
#include "rclcpp/publisher_base.hpp"

#include "rcl/allocator.h"
#include "rcl/publisher.h"

namespace rclcpp
{

template<typename MessageT, typename AllocatorT = std::allocator<void>>
class LoanedMessage
{
  using MessageAllocatorTraits = rclcpp::allocator::AllocRebind<MessageT, AllocatorT>;
  using MessageAllocator = typename MessageAllocatorTraits::allocator_type;

public:

  LoanedMessage(
    const rclcpp::PublisherBase & pub,
    std::allocator<MessageT> allocator)
  : pub_(pub),
    message_(nullptr),
    message_allocator_(std::move(allocator))
  {
    if (pub_.can_loan_messages()) {
      void * message_ptr = nullptr;
      auto ret = rcl_borrow_loaned_message(
        pub_.get_publisher_handle(),
        rosidl_typesupport_cpp::get_message_type_support_handle<MessageT>(),
        &message_ptr);
      if (RCL_RET_OK != ret) {
        rclcpp::exceptions::throw_from_rcl_error(ret);
      }
      message_ = static_cast<MessageT *>(message_ptr);
    } else {
      RCLCPP_INFO_ONCE(
        rclcpp::get_logger("rclcpp"),
        "Currently used middleware can't loan messages. Local allocator will be used.");
      message_ = message_allocator_.allocate(1);
      new (message_) MessageT();
    }
  }


  LoanedMessage(
    const rclcpp::PublisherBase * pub,
    std::shared_ptr<std::allocator<MessageT>> allocator)
  : LoanedMessage(*pub, *allocator)
  {}

  LoanedMessage(LoanedMessage<MessageT> && other)
  : pub_(std::move(other.pub_)),
    message_(std::move(other.message_)),
    message_allocator_(std::move(other.message_allocator_))
  {}


  virtual ~LoanedMessage()
  {
    auto error_logger = rclcpp::get_logger("LoanedMessage");

    if (message_ == nullptr) {
      return;
    }

    if (pub_.can_loan_messages()) {
      // return allocated memory to the middleware
      auto ret =
        rcl_return_loaned_message_from_publisher(pub_.get_publisher_handle(), message_);
      if (ret != RCL_RET_OK) {
        RCLCPP_ERROR(
          error_logger, "rcl_deallocate_loaned_message failed: %s", rcl_get_error_string().str);
        rcl_reset_error();
      }
    } else {
      // call destructor before deallocating
      message_->~MessageT();
      message_allocator_.deallocate(message_, 1);
    }
    message_ = nullptr;
  }


  bool is_valid() const
  {
    return message_ != nullptr;
  }


  MessageT & get() const
  {
    return *message_;
  }


  MessageT * release()
  {
    auto msg = message_;
    message_ = nullptr;
    return msg;
  }

protected:
  const rclcpp::PublisherBase & pub_;

  MessageT * message_;

  MessageAllocator message_allocator_;

  LoanedMessage(const LoanedMessage<MessageT> & other) = delete;
};

}  // namespace rclcpp

#endif  // RCLCPP__LOANED_MESSAGE_HPP_