threaded_event_scheduler.h

#pragma once

// This component provides a `class`, `ThreadedEventScheduler`, that implements
// the `EventScheduler` interface in terms of a dedicated event dispatching
// thread. It is the default implementation used if
// `DatadogAgent::event_scheduler` is not specified.

#include <datadog/event_scheduler.h>

#include <chrono>
#include <condition_variable>
#include <functional>
#include <memory>
#include <mutex>
#include <queue>
#include <thread>
#include <vector>

namespace datadog {
namespace tracing {

class ThreadedEventScheduler : public EventScheduler {
  struct EventConfig {
    std::function<void()> callback;
    std::chrono::steady_clock::duration interval;
    bool cancelled;

    EventConfig(std::function<void()> callback,
                std::chrono::steady_clock::duration interval);
  };

  struct ScheduledRun {
    std::chrono::steady_clock::time_point when;
    std::shared_ptr<const EventConfig> config;
  };

  struct GreaterThan {
    bool operator()(const ScheduledRun&, const ScheduledRun&) const;
  };

  std::mutex mutex_;
  ScheduledRun current_;
  std::condition_variable schedule_or_shutdown_;
  bool running_current_;
  std::condition_variable current_done_;
  std::priority_queue<ScheduledRun, std::vector<ScheduledRun>, GreaterThan>
      upcoming_;
  bool shutting_down_;
  std::thread dispatcher_;

  void run();

 public:
  ThreadedEventScheduler();
  ~ThreadedEventScheduler();

  Cancel schedule_recurring_event(std::chrono::steady_clock::duration interval,
                                  std::function<void()> callback) override;

  std::string config() const override;
};

}  // namespace tracing
}  // namespace datadog