control_plane_locks.h

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#pragma once
 
#include <condition_variable>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <mutex>
#include <semaphore>
#include <shared_mutex>
 
namespace mm::comm {
 
class BusLock {
 public:
  void lock();
  void unlock();
  void lock_shared();
  void unlock_shared();
 
 private:
  std::mutex mutex_;
  std::condition_variable readerCanEnter_;
  std::condition_variable writerCanEnter_;
  int readers_ = 0;
  int writersWaiting_ = 0;
  bool writer_ = false;
};
 
class FrameSlot {
 public:
  explicit FrameSlot(std::counting_semaphore<>& slots);
  ~FrameSlot();
  FrameSlot(FrameSlot&& other) noexcept;
  FrameSlot(const FrameSlot&) = delete;
  FrameSlot& operator=(const FrameSlot&) = delete;
  FrameSlot& operator=(FrameSlot&&) = delete;
 
 private:
  std::counting_semaphore<>* slots_;
};
 
struct DriveLock {
  std::shared_lock<BusLock> bus;
  std::unique_lock<std::mutex> drive;
  FrameSlot frame;
};
 
struct BusIoLock {
  std::shared_lock<BusLock> bus;
  FrameSlot frame;
};
 
class ControlPlaneLocks {
 public:
  static constexpr std::ptrdiff_t kFrameSlots = 8;
 
  explicit ControlPlaneLocks(std::size_t positions);
 
  [[nodiscard]] std::unique_lock<BusLock> lockBus();
 
  [[nodiscard]] std::shared_lock<BusLock> lockBusShared();
 
  [[nodiscard]] BusIoLock lockBusIo();
 
  [[nodiscard]] DriveLock lockDrive(uint16_t position);
 
 private:
  BusLock bus_;
  std::unique_ptr<std::mutex[]> drives_;
  std::counting_semaphore<> frameSlots_{kFrameSlots};
};
 
}  // namespace mm::comm