drain.hh

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#ifndef __SIM_DRAIN_HH__
#define __SIM_DRAIN_HH__

#include <atomic>
#include <mutex>
#include <vector>

class Drainable;

enum class DrainState {
    Running,  
    Draining, 
    Drained,  
    Resuming, 
};

class DrainManager
{
  private:
    DrainManager();
    DrainManager(DrainManager &) = delete;
    ~DrainManager();

  public:
    static DrainManager &instance() { return _instance; }

    bool tryDrain();

    void resume();

    void preCheckpointRestore();

    bool isDrained() const { return _state == DrainState::Drained; }

    DrainState state() const { return _state; }

    void signalDrainDone();

  public:
    void registerDrainable(Drainable *obj);
    void unregisterDrainable(Drainable *obj);

  private:
    bool allInState(DrainState state) const;

    size_t drainableCount() const;

    mutable std::mutex globalLock;

    std::vector<Drainable *> _allDrainable;

    std::atomic_uint _count;

    DrainState _state;

    static DrainManager _instance;
};

class Drainable
{
    friend class DrainManager;

  protected:
    Drainable();
    virtual ~Drainable();

    virtual DrainState drain() = 0;

    virtual void drainResume() {};

    void signalDrainDone() const {
        switch (_drainState) {
          case DrainState::Running:
          case DrainState::Drained:
          case DrainState::Resuming:
            return;
          case DrainState::Draining:
            _drainState = DrainState::Drained;
            _drainManager.signalDrainDone();
            return;
        }
    }

  public:
    DrainState drainState() const { return _drainState; }

    virtual void notifyFork() {};

  private:
    DrainState dmDrain();
    void dmDrainResume();

    DrainManager &_drainManager;

    mutable DrainState _drainState;
};

#endif