Method _more_tasks

src/bthread/execution_queue_inl.h:483–527

---------------------ExecutionQueueBase--------------------

// ---------------------ExecutionQueueBase--------------------
inline bool ExecutionQueueBase::_more_tasks(
        TaskNode* old_head, TaskNode** new_tail, 
        bool has_uniterated) {

    CHECK(old_head->next == NULL);
    // Try to set _head to NULL to mark that the execute is done.
    TaskNode* new_head = old_head;
    TaskNode* desired = NULL;
    bool return_when_no_more = false;
    if (has_uniterated) {
        desired = old_head;
        return_when_no_more = true;
    }
    if (_head.compare_exchange_strong(
                new_head, desired, butil::memory_order_acquire)) {
        // No one added new tasks.
        return return_when_no_more;
    }
    CHECK_NE(new_head, old_head);
    // Above acquire fence pairs release fence of exchange in Write() to make
    // sure that we see all fields of requests set.

    // Someone added new requests.
    // Reverse the list until old_head.
    TaskNode* tail = NULL;
    if (new_tail) {
        *new_tail = new_head;
    }
    TaskNode* p = new_head;
    do {
        while (p->next == TaskNode::UNCONNECTED) {
            // TODO(gejun): elaborate this
            sched_yield();
        }
        TaskNode* const saved_next = p->next;
        p->next = tail;
        tail = p;
        p = saved_next;
        CHECK(p != NULL);
    } while (p != old_head);

    // Link old list with new list.
    old_head->next = tail;
    return true;
}

inline int ExecutionQueueBase::dereference() {
    const uint64_t vref = _versioned_ref.fetch_sub(