wait_result.hpp

// Copyright 2020 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__WAIT_RESULT_HPP_
#define RCLCPP__WAIT_RESULT_HPP_
 
#include <cassert>
#include <functional>
#include <stdexcept>
 
#include "rcl/wait.h"
 
#include "rclcpp/macros.hpp"
#include "rclcpp/wait_result_kind.hpp"
 
namespace rclcpp
{
 
// TODO(wjwwood): the union-like design of this class could be replaced with
//   std::variant, when we have access to that...
 
template<class WaitSetT>
class WaitResult final
{
public:
 
  static
  WaitResult
  from_ready_wait_result_kind(WaitSetT & wait_set)
  {
    return WaitResult(WaitResultKind::Ready, wait_set);
  }
 
  static
  WaitResult
  from_timeout_wait_result_kind()
  {
    return WaitResult(WaitResultKind::Timeout);
  }
 
  static
  WaitResult
  from_empty_wait_result_kind()
  {
    return WaitResult(WaitResultKind::Empty);
  }
 
  WaitResultKind
  kind() const
  {
    return wait_result_kind_;
  }
 
 
  const WaitSetT &
  get_wait_set() const
  {
    if (this->kind() != WaitResultKind::Ready) {
      throw std::runtime_error("cannot access wait set when the result was not ready");
    }
    // This should never happen, defensive (and debug mode) check only.
    assert(wait_set_pointer_);
    return *wait_set_pointer_;
  }
 
 
  WaitSetT &
  get_wait_set()
  {
    if (this->kind() != WaitResultKind::Ready) {
      throw std::runtime_error("cannot access wait set when the result was not ready");
    }
    // This should never happen, defensive (and debug mode) check only.
    assert(wait_set_pointer_);
    return *wait_set_pointer_;
  }
 
  WaitResult(WaitResult && other) noexcept
  : wait_result_kind_(other.wait_result_kind_),
    wait_set_pointer_(std::exchange(other.wait_set_pointer_, nullptr))
  {}
 
  ~WaitResult()
  {
    if (wait_set_pointer_) {
      wait_set_pointer_->wait_result_release();
    }
  }
 
private:
  RCLCPP_DISABLE_COPY(WaitResult)
 
  explicit WaitResult(WaitResultKind wait_result_kind)
  : wait_result_kind_(wait_result_kind)
  {
    // Should be enforced by the static factory methods on this class.
    assert(WaitResultKind::Ready != wait_result_kind);
  }
 
  WaitResult(WaitResultKind wait_result_kind, WaitSetT & wait_set)
  : wait_result_kind_(wait_result_kind),
    wait_set_pointer_(&wait_set)
  {
    // Should be enforced by the static factory methods on this class.
    assert(WaitResultKind::Ready == wait_result_kind);
    // Secure thread-safety (if provided) and shared ownership (if needed).
    wait_set_pointer_->wait_result_acquire();
  }
 
  const WaitResultKind wait_result_kind_;
 
  WaitSetT * wait_set_pointer_ = nullptr;
};
 
}  // namespace rclcpp
 
#endif  // RCLCPP__WAIT_RESULT_HPP_