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 * Copyright (c) 2015 - 2018, Nordic Semiconductor ASA
 * 
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 * are permitted provided that the following conditions are met:
 * 
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 *    list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 * 
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 * 
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 * 
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 * 
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
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 */
/** @file
 * @defgroup nrf_mtx nRF Mutex
 * @{
 * @ingroup app_common
 * @brief Mutex used for protecting resources.
 *
 * This module provides a mutex that can be used to ensure only one context may enter a critical
 * section holding the lock.
 */
#ifndef NRF_MTX_H__
#define NRF_MTX_H__

#include <stdint.h>
#include <stdbool.h>
#include "nrf.h"
#include "nrf_atomic.h"
#include "nrf_assert.h"

#define NRF_MTX_LOCKED      1
#define NRF_MTX_UNLOCKED    0

/**
 * @brief Mutex data type.
 *
 * All fields in this struct are internal, and should never be modified outside of the nrf_mtx_*
 * functions.
 */
typedef nrf_atomic_u32_t nrf_mtx_t;

/**
 * @brief Initialize mutex.
 *
 * This function _must_ be called before nrf_mtx_trylock() and nrf_mtx_unlock() functions.
 *
 * @param[in, out] p_mtx The mutex to be initialized.
 */
__STATIC_INLINE void nrf_mtx_init(nrf_mtx_t * p_mtx);


/**
 * @brief Destroy mutex.
 *
 * This function can be used in abort scenarios or when the mutex is no longer to be used.
 *
 * @param[in] p_mtx The mutex to be destroy.
 */
__STATIC_INLINE void nrf_mtx_destroy(nrf_mtx_t * p_mtx);

/**
 * @brief Try to lock a mutex.
 *
 * If the mutex is already held by another context, this function will return immediately.
 *
 * @param[in, out] p_mtx The mutex to be locked.
 * @return true if lock was acquired, false if not
 */
__STATIC_INLINE bool nrf_mtx_trylock(nrf_mtx_t * p_mtx);

/**
 * @brief Unlock a mutex.
 *
 * This function _must_ only be called when holding the lock. Unlocking a mutex which you do not
 * hold will give undefined behavior.
 *
 * @note Unlock must happen from the same context as the one used to lock the mutex.
 *
 * @param[in, out] p_mtx The mutex to be unlocked.
 */
__STATIC_INLINE void nrf_mtx_unlock(nrf_mtx_t * p_mtx);

#ifndef SUPPRESS_INLINE_IMPLEMENTATION

__STATIC_INLINE void nrf_mtx_init(nrf_mtx_t * p_mtx)
{
    ASSERT(p_mtx  != NULL);

    *p_mtx = NRF_MTX_UNLOCKED;
    __DMB();
}

__STATIC_INLINE void nrf_mtx_destroy(nrf_mtx_t * p_mtx)
{
    ASSERT(p_mtx  != NULL);

    // Add memory barrier to ensure that any memory operations protected by the mutex complete
    // before the mutex is destroyed.
    __DMB();

    *p_mtx = NRF_MTX_UNLOCKED;
}

__STATIC_INLINE bool nrf_mtx_trylock(nrf_mtx_t * p_mtx)
{
    ASSERT(p_mtx  != NULL);

    uint32_t old_val = nrf_atomic_u32_fetch_store(p_mtx, NRF_MTX_LOCKED);

    // Add memory barrier to ensure that the mutex is locked before any memory operations protected
    // by the mutex are started.
    __DMB();

    return (old_val == NRF_MTX_UNLOCKED);
}

__STATIC_INLINE void nrf_mtx_unlock(nrf_mtx_t * p_mtx)
{
    ASSERT(p_mtx  != NULL);
    ASSERT(*p_mtx == NRF_MTX_LOCKED);

    // Add memory barrier to ensure that any memory operations protected by the mutex complete
    // before the mutex is unlocked.
    __DMB();

    *p_mtx = NRF_MTX_UNLOCKED;
}

#endif //SUPPRESS_INLINE_IMPLEMENTATION

#endif // NRF_MTX_H__
/** @} */