watchdog.h

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// Copyright (c) 2020-2021 Pilz GmbH & Co. KG
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
#ifndef PSEN_SCAN_V2_STANDALONE_WATCHDOG_H
#define PSEN_SCAN_V2_STANDALONE_WATCHDOG_H
 
#include <chrono>
#include <functional>
#include <thread>
#include <atomic>
#include <condition_variable>
 
#include "psen_scan_v2_standalone/util/async_barrier.h"
 
namespace psen_scan_v2_standalone
{
namespace util
{
class Watchdog
{
public:
  using Timeout = const std::chrono::high_resolution_clock::duration;
 
public:
  Watchdog(const Timeout& timeout, const std::function<void()>& timeout_callback);
  ~Watchdog();
 
public:
  void reset();
 
private:
  std::cv_status waitFor(const Timeout& timeout);
 
private:
  util::Barrier thread_startetd_barrier_;
  std::atomic_bool terminated_{ false };
  std::condition_variable cv_;
  std::mutex cv_m_;
  std::thread timer_thread_;
};
 
inline Watchdog::Watchdog(const Timeout& timeout, const std::function<void()>& timeout_callback)
  : timer_thread_([this, timeout, timeout_callback]() {
    thread_startetd_barrier_.release();
    while (!terminated_)
    {
      if ((this->waitFor(timeout) == std::cv_status::timeout) && !terminated_)
      {
        timeout_callback();
      }
    }
  })
{
  // The timer_thread does not always immediately start because the system schedules threads
  // "at a whim". To ensure that the thread is running after the completion of the constructor,
  // we wait until the first command of the thread is executed.
  if (!thread_startetd_barrier_.waitTillRelease(timeout))
  {
    // Difficult to test because this is a timing problem.
    // LCOV_EXCL_START
    throw std::runtime_error("Timeout while waiting for timer thread to start");
    // LCOV_EXCL_STOP
  }
}
 
inline std::cv_status Watchdog::waitFor(const Timeout& timeout)
{
  std::unique_lock<std::mutex> lk(cv_m_);
  return cv_.wait_for(lk, timeout);
}
 
inline void Watchdog::reset()
{
  cv_.notify_all();
}
 
inline Watchdog::~Watchdog()
{
  terminated_ = true;
  // Notify timeout thread to wake up and end execution
  cv_.notify_all();
  if (timer_thread_.joinable())
  {
    timer_thread_.join();
  }
}
 
}  // namespace util
}  // namespace psen_scan_v2_standalone
 
#endif  // PSEN_SCAN_V2_STANDALONE_WATCHDOG_H