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amiro-os / include / amiro / util / rwlock.hpp @ 58fe0e0b

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1 58fe0e0b Thomas Schöpping
#ifndef AMIRO_RWLOCK_H_
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#define AMIRO_RWLOCK_H_
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#include <ch.hpp>
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namespace amiro {
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/**
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 * @brief An enhanced mutex with parallel read but exclusive write capabilities
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 */
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class RWLock
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{
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public:
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  /**
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   * @brief An enum to specify the favoritism of the RWLock
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   */
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  enum Favor : bool {
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    FAVOR_READERS = false, /**< Favors readers, even if writers are waiting */
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    FAVOR_WRITERS = true,  /**< Favors writers and holds new readers back */
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  };
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  /**
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   * @brief An enum to specify what to wait for in the tryLockReading() and tryLockWriting() methods.
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   */
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  enum WaitingType : uint8_t {
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    WAIT_FOR_NONE = 0,  /**< does not block at all */
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    WAIT_FOR_MUTEX = 1, /**< blocks at the mutex */
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    WAIT_FOR_QUEUE = 2, /**< waits for the queues */
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  };
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private:
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  /**
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   * @brief A status struct holding the current configuration of the RWLock.
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   */
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  struct AccessStatus {
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    uint8_t reader_count : 7; /**< The number of currently active readers (128 max) */
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    uint8_t favor        : 1; /**< The currently selected favoritism */
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  };
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  chibios_rt::Mutex mutex;             /**< A mutex lock used for synchronization */
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  chibios_rt::CondVar waiting_readers; /**< A condition variable for waiting readers */
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  chibios_rt::CondVar waiting_writers; /**< A condition variable for all waiting writers */
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  AccessStatus status;                 /**< The current status of the RWLock */
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public:
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  /**
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   * @brief Constructor of the RWLock class.
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   * @param[in] favor The initial favoritism (default: FAVOR_WRITERS)
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   */
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  explicit RWLock(const Favor favor = FAVOR_WRITERS);
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  /**
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   * @brief Destructor of the RWLock class.
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   */
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  virtual ~RWLock();
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  /**
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   * @brief Lock the RWLock as a reader (shared mode)
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   */
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  void lockReading();
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  /**
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   * @brief Lock the RWLock as a writer (exclusive mode)
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   */
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  void lockWriting();
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  /**
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   * @brief Try to lock the RWLock as a reader (shared mode) but do not block
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   * @param[in] wait Can be used to wait for the mutex to lock or the queue to be empty
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   * @return True if the RWLock was successfully locked; False if not
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   */
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  bool tryLockReading(const WaitingType wait = WAIT_FOR_NONE);
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  /**
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   * @brief Try to lock the RWLock as a writer (exclusive mode) but do not block
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   * @param[in] wait Can be used to wait for the mutex to lock or the queue to be empty
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   * @return True if the RWLock was successfully locked; False if not
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   */
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  bool tryLockWriting(const WaitingType wait = WAIT_FOR_NONE);
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  /**
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   * @brief Unlocks the RWLock.
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   * If it was locked in shared or exclusive mode is detected automatically.
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   */
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  void unlock();
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  /**
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   * @brief Set the favoritism of the RWLock
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   * @param[in] favor Either FAVOR_READERS or FAVOR_WRITERS
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   */
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  void setFavoritism(const Favor favor);
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  /**
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   * @brief Try to set the favoritism of the RWLock but do not block
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   * @param[in] favor Either FAVOR_READERS or FAVOR_WRITERS
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   * @return True if the favoritism was successfully set; False if not
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   */
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  bool trySetFavoritism(const Favor favor);
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};
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} // end of namespace amiro
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#endif // AMIRO_RWLOCK_H_