st_thread_yield主动切换协程—SRS对StateThreads的改进与完善

作者：罗上文，微信：Loken1，公众号：FFmpeg弦外之音

待写，下面是草稿。

void st_thread_yield()
{
    _st_thread_t *me = _ST_CURRENT_THREAD();

    #if defined(DEBUG) && defined(DEBUG_STATS)
    ++_st_stat_thread_yield;
    #endif

    /* Check sleep queue for expired threads */
    _st_vp_check_clock();

    // If not thread in RunQ to yield to, ignore and continue to run.
    if (_ST_RUNQ.next == &_ST_RUNQ) {
        return;
    }

    #if defined(DEBUG) && defined(DEBUG_STATS)
    ++_st_stat_thread_yield2;
    #endif

    // Append thread to the tail of RunQ, we will back after all threads executed.
    me->state = _ST_ST_RUNNABLE;
    _ST_ADD_RUNQ(me);

    // Yield to other threads in the RunQ.
    _ST_SWITCH_CONTEXT(me);
}