Operating system and interrupts

Operating system and interrupts

LVGL is not thread-safe by default.

However, in the following conditions it’s valid to call LVGL related functions:

• In events. Learn more in Events.
• In lv_timer. Learn more in Timers.

Tasks and threads

If you need to use real tasks or threads, you need a mutex which should be invoked before the call of lv_timer_handler and released after it. Also, you have to use the same mutex in other tasks and threads around every LVGL (lv_...) related function call and code. This way you can use LVGL in a real multitasking environment. Just make use of a mutex to avoid the concurrent calling of LVGL functions.

Here is some pseudocode to illustrate the concept:

static mutex_t lvgl_mutex;

void lvgl_thread(void)
{
    while(1) {
        mutex_lock(&lvgl_mutex);
        lv_task_handler();
        mutex_unlock(&lvgl_mutex);
        thread_sleep(10); /* sleep for 10 ms */
    }
}

void other_thread(void)
{
    /* You must always hold the mutex while using LVGL APIs */
    mutex_lock(&lvgl_mutex);
    lv_obj_t *img = lv_img_create(lv_scr_act());
    mutex_unlock(&lvgl_mutex);
    
    while(1) {
        mutex_lock(&lvgl_mutex);
        /* change to the next image */
        lv_img_set_src(img, next_image);
        mutex_unlock(&lvgl_mutex);
        thread_sleep(2000);
    }
}

Interrupts

Try to avoid calling LVGL functions from interrupt handlers (except lv_tick_inc() and lv_disp_flush_ready()). But if you need to do this you have to disable the interrupt which uses LVGL functions while lv_timer_handler is running.

It’s a better approach to simply set a flag or some value in the interrupt, and periodically check it in an LVGL timer (which is run by lv_timer_handler).