Function _rt_sem_take

src/ipc.c:558–643

* @brief This function will take a semaphore, if the semaphore is unavailable, the thread shall wait for * the semaphore up to a specified time. * * @note When this function is called, the count value of the sem->value will decrease 1 until it is equal to 0. * When the sem->value is 0, it means that the semaphore is unavailable. At this time, it will suspend the *

 * @warning  This function can ONLY be called in the thread context. It MUST NOT BE called in interrupt context.
 */
static rt_err_t _rt_sem_take(rt_sem_t sem, rt_int32_t timeout, int suspend_flag)
{
    rt_base_t level;
    struct rt_thread *thread;
    rt_err_t ret;

    /* parameter check */
    RT_ASSERT(sem != RT_NULL);
    RT_ASSERT(rt_object_get_type(&sem->parent.parent) == RT_Object_Class_Semaphore);

    RT_OBJECT_HOOK_CALL(rt_object_trytake_hook, (&(sem->parent.parent)));

    /* current context checking */
    RT_DEBUG_SCHEDULER_AVAILABLE(1);

    level = rt_spin_lock_irqsave(&(sem->spinlock));

    LOG_D("thread %s take sem:%s, which value is: %d",
          rt_thread_self()->parent.name,
          sem->parent.parent.name,
          sem->value);

    if (sem->value > 0)
    {
        /* semaphore is available */
        sem->value --;
        rt_spin_unlock_irqrestore(&(sem->spinlock), level);
    }
    else
    {
        /* no waiting, return with timeout */
        if (timeout == 0)
        {
            rt_spin_unlock_irqrestore(&(sem->spinlock), level);
            return -RT_ETIMEOUT;
        }
        else
        {
            /* semaphore is unavailable, push to suspend list */
            /* get current thread */
            thread = rt_thread_self();

            /* reset thread error number */
            thread->error = RT_EINTR;

            LOG_D("sem take: suspend thread - %s", thread->parent.name);

            /* suspend thread */
            ret = rt_thread_suspend_to_list(thread, &(sem->parent.suspend_thread),
                                            sem->parent.parent.flag, suspend_flag);
            if (ret != RT_EOK)
            {
                rt_spin_unlock_irqrestore(&(sem->spinlock), level);
                return ret;
            }

            /* has waiting time, start thread timer */
            if (timeout > 0)