Function _wait_for_event

components/lwp/lwp_pid.c:1460–1509

* @brief Wait for a child process status change event * * @param[in] cur_thr Current thread context that will be suspended * @param[in] self_lwp Lightweight process (parent) waiting for the event * @param[in,out] handle Waitpid handle containing filter criteria and wait queue node * @param[in] destiny Process ID or process group to wait for (-1 for any child, -pgid for process group) * * @r

 *       event that matches the specified criteria (process ID or process group).
 */
static rt_err_t _wait_for_event(rt_thread_t cur_thr, rt_lwp_t self_lwp,
                                struct waitpid_handle *handle, pid_t destiny)
{
    rt_err_t ret;

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

    handle->wq_node.polling_thread = cur_thr;
    handle->wq_node.key = destiny;
    handle->wq_node.wakeup = _waitq_filter;
    handle->wq_node.wqueue = &self_lwp->waitpid_waiters;
    rt_list_init(&handle->wq_node.list);

    cur_thr->error = RT_EOK;

    LOG_D("%s(self_lwp=%d) wait for event", __func__, self_lwp->pid);

    rt_enter_critical();
    ret = rt_thread_suspend_with_flag(cur_thr, RT_INTERRUPTIBLE);
    if (ret == RT_EOK)
    {
        rt_wqueue_add(handle->wq_node.wqueue, &handle->wq_node);
        rt_exit_critical();

        rt_schedule();

        ret = cur_thr->error;

        /**
         * cur_thr error is a positive value, but some legacy implementation
         * use a negative one. So we check to avoid errors
         */
        ret = ret > 0 ? -ret : ret;

        /**
         * we dont rely on this actually, but we cleanup it since wakeup API
         * set this up durint operation, and this will cause some messy condition
         */
        handle->wq_node.wqueue->flag = RT_WQ_FLAG_CLEAN;
        rt_wqueue_remove(&handle->wq_node);
    }
    else
    {
        /* failed to suspend, return immediately with failure */
        rt_exit_critical();
    }

    return ret;
}

/**
 * @brief Wait for and reap a child process status change