status_monitor.hpp

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// Copyright 2015 TIER IV, 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 STATUS_MONITOR__STATUS_MONITOR_HPP_
#define STATUS_MONITOR__STATUS_MONITOR_HPP_
 
#include <cerrno>
#include <chrono>
#include <filesystem>
#include <fstream>
#include <mutex>
#include <thread>
#include <unordered_map>
#include <utility>
 
namespace common
{
class StatusMonitor
{
  struct Status
  {
    const std::string name;
 
    std::chrono::high_resolution_clock::time_point last_access;
 
    using duration = std::chrono::high_resolution_clock::duration;
 
    duration minimum_access_interval;
 
    duration maximum_access_interval;
 
    bool exited = false;
 
    template <typename Name>
    explicit Status(Name && name)
    : name(std::forward<decltype(name)>(name)),
      last_access(std::chrono::high_resolution_clock::now()),
      minimum_access_interval(duration::max()),
      maximum_access_interval(duration::min())
    {
    }
 
    auto since_last_access() const
    {
      return std::chrono::high_resolution_clock::now() - last_access;
    }
 
    auto good() const { return exited or since_last_access() < threshold; }
 
    explicit operator bool() const { return good(); }
  };
 
  static inline std::ofstream file;
 
  static inline std::unordered_map<std::thread::id, Status> statuses;
 
  static inline std::thread watchdog;
 
  static inline std::atomic_bool terminating;
 
  static inline std::chrono::seconds threshold = std::chrono::seconds(10);
 
  static inline std::mutex mutex;
 
public:
  explicit StatusMonitor();
 
  ~StatusMonitor();
 
  template <typename Name>
  auto touch(Name && name)
  {
    auto lock = std::scoped_lock<std::mutex>(mutex);
 
    if (auto iter = statuses.find(std::this_thread::get_id()); iter != std::end(statuses)) {
      [[maybe_unused]] auto && [id, status] = *iter;
 
      const auto now = std::chrono::high_resolution_clock::now();
 
      const auto this_access_interval = now - status.last_access;
 
      status.minimum_access_interval =
        std::min(status.minimum_access_interval, this_access_interval);
 
      status.maximum_access_interval =
        std::max(status.maximum_access_interval, this_access_interval);
 
      status.last_access = now;
    } else {
      statuses.emplace(std::this_thread::get_id(), std::forward<decltype(name)>(name));
    }
  }
 
  template <typename T>
  class ScopedExchanger
  {
    std::reference_wrapper<T> target;
 
    T value;
 
  public:
    template <typename... Ts>
    static auto locked_exchange(Ts &&... xs) -> decltype(auto)
    {
      auto lock = std::scoped_lock<std::mutex>(mutex);
      return std::exchange(std::forward<decltype(xs)>(xs)...);
    }
 
    template <typename U>
    explicit ScopedExchanger(T & x, U && y)
    : target(x), value(locked_exchange(target.get(), std::forward<decltype(y)>(y)))
    {
    }
 
    ~ScopedExchanger() { locked_exchange(target.get(), value); }
  };
 
  struct ScopedUpdater
  {
    StatusMonitor & monitor;
    explicit ScopedUpdater(StatusMonitor & m) : monitor(m) { monitor.touch(""); }
    ~ScopedUpdater() { monitor.touch(""); }
  };
 
  template <typename Thunk>
  auto overrideThreshold(const std::chrono::seconds & t, Thunk thunk) -> decltype(auto)
  {
    auto exchanger = ScopedExchanger(threshold, t);
    auto updater = ScopedUpdater(*this);
 
    return thunk();
  }
 
  auto write() const -> void;
} static status_monitor;
}  // namespace common
 
#endif  // STATUS_MONITOR__STATUS_MONITOR_HPP_