Function _futex_cmpxchg_value

components/lwp/lwp_futex.c:500–519

* @brief Compare and exchange futex value atomically * * @param[out] curval Pointer to store the current value if exchange fails * @param[in] uaddr User-space address of the futex value * @param[in] uval Expected value to compare against * @param[in] newval New value to set if comparison succeeds * * @return int Returns 0 on success, -EFAULT if address is inaccessible, * or -EAGAIN

 * @note Checks user address accessibility before operation
 */
rt_inline int _futex_cmpxchg_value(int *curval, int *uaddr, int uval,
                                   int newval)
{
    int err = 0;

    if (!lwp_user_accessable((void *)uaddr, sizeof(*uaddr)))
    {
        err = -EFAULT;
        goto exit;
    }

    if (!atomic_compare_exchange_strong(uaddr, &uval, newval))
    {
        *curval = uval;
        err = -EAGAIN;
    }

exit:
    return err;
}

/**
 * @brief Wait on a futex if its value matches the expected value.