rtos：zephyr同步alerts（通知）

alert可以同linux平臺下的signal。
alert的初始化：

方法1：

extern int my_alert_handler(struct k_alert *alert);

struct k_alert my_alert;

k_alert_init(&my_alert, my_alert_handler, 10);

方法2：

extern int my_alert_handler(struct k_alert *alert);

K_ALERT_DEFINE(my_alert, my_alert_handler, 10);

發出一個alert：

extern int my_alert_handler(struct k_alert *alert);

K_ALERT_DEFINE(my_alert, my_alert_handler, 10);

void keypress_interrupt_handler(void *arg)
{
    ...
    k_alert_send(&my_alert);
    ...
}

處理一個alert：

int <function_name>(struct k_alert *alert)
{
    /* catch the alert signal; return zero if the signal is consumed, */
    /* or non-zero to let the alert pend                              */
    ...
}
int my_alert_handler(struct k_alert *alert_id_is_unused)
{
    /* determine what key was pressed */
    char c = get_keypress();

    /* do complex processing of the keystroke */
    ...

    /* signaled alert has been consumed */
    return 0;
}

接收一個alert：

int my_alert_handler(struct k_alert *alert_id_is_unused)
{
    /* determine what key was pressed */
    char c = get_keypress();

    /* signal thread only if key pressed was a digit */
    if ((c >= '0') && (c <= '9')) {
        /* save key press information */
        ...
        /* signaled alert should be pended */
        return 1;
    } else {
        /* signaled alert has been consumed */
        return 0;
    }
}

void keypress_thread(void *unused1, void *unused2, void *unused3)
{
    /* consume numeric key presses */
    while (1) {

        /* wait for a key press alert to pend */
        k_alert_recv(&my_alert, K_FOREVER);

        /* process saved key press, which must be a digit */
        ...
    }
}

一個掛起的的alter可以通過另一個線程調用k_alert_recv()接口接收這個alter。