Function _futex_requeue

components/lwp/lwp_futex.c:666–731

* @brief Requeue threads from one futex waiting list to another * * @param[in] futex1 Source futex containing threads to wake/requeue * @param[in] futex2 Destination futex for requeued threads * @param[in] lwp Lightweight process structure * @param[in] nr_wake Maximum number of threads to wake from futex1 * @param[in] nr_requeue Maximum number of threads to requeue to futex2 * @param[in] op

 *       on futex1 into the waiting queue of futex2.
 */
static long _futex_requeue(rt_futex_t futex1, rt_futex_t futex2,
                           struct rt_lwp *lwp, int nr_wake, int nr_requeue,
                           int opflags)
{
    long rtn;
    long woken_cnt = 0;
    int is_empty = 0;
    rt_thread_t thread;

    if (futex1 == futex2)
    {
        return -EINVAL;
    }

    /**
     * Brief: Wakeup a suspended thread on the futex waiting thread list
     *
     * Note: Critical Section
     * - the futex waiting_thread list (RW)
     */
    while (nr_wake && !is_empty)
    {
        if (rt_susp_list_dequeue(&futex1->waiting_thread, RT_EOK))
        {
            nr_wake--;
            woken_cnt++;
            is_empty = RT_FALSE;
        }
        else
        {
            is_empty = RT_TRUE;
        }
    }
    rtn = woken_cnt;

    /**
     * Brief: Requeue
     *
     * Note: Critical Section
     * - the futex waiting_thread list (RW)
     */
    while (!is_empty && nr_requeue)
    {
        rt_sched_lock_level_t slvl;
        rt_sched_lock(&slvl);

        /* moving from one susp list to another */
        is_empty = rt_list_isempty(&(futex1->waiting_thread));

        if (!is_empty)
        {
            thread = RT_THREAD_LIST_NODE_ENTRY(futex1->waiting_thread.next);
            rt_list_remove(&RT_THREAD_LIST_NODE(thread));
            rt_list_insert_before(&(futex2->waiting_thread),
                                  &RT_THREAD_LIST_NODE(thread));
            nr_requeue--;
            rtn++;
        }