Function start_from_non_worker

src/bthread/bthread.cpp:268–294

__thread TaskGroup* tls_task_group_nosignal = NULL;

BUTIL_FORCE_INLINE int
start_from_non_worker(bthread_t* __restrict tid,
                      const bthread_attr_t* __restrict attr,
                      void* (*fn)(void*),
                      void* __restrict arg) {
    TaskControl* c = get_or_new_task_control();
    if (NULL == c) {
        return ENOMEM;
    }
    auto tag = BTHREAD_TAG_DEFAULT;
    if (attr != NULL && attr->tag != BTHREAD_TAG_INVALID) {
        tag = attr->tag;
    }
    if (attr != NULL && (attr->flags & BTHREAD_NOSIGNAL)) {
        // Remember the TaskGroup to insert NOSIGNAL tasks for 2 reasons:
        // 1. NOSIGNAL is often for creating many bthreads in batch,
        //    inserting into the same TaskGroup maximizes the batch.
        // 2. bthread_flush() needs to know which TaskGroup to flush.
        auto g = tls_task_group_nosignal;
        if (NULL == g) {
            g = c->choose_one_group(tag);
            tls_task_group_nosignal = g;
        }
        return g->start_background<true>(tid, attr, fn, arg);
    }
    return c->choose_one_group(tag)->start_background<true>(tid, attr, fn, arg);
}

// Meet one of the three conditions, can run in thread local
// attr is nullptr