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