Function butex_requeue

src/bthread/butex.cpp:461–499

}

int butex_requeue(void* arg, void* arg2) {
    Butex* b = container_of(static_cast<butil::atomic<int>*>(arg), Butex, value);
    Butex* m = container_of(static_cast<butil::atomic<int>*>(arg2), Butex, value);

    ButexWaiter* front = NULL;
    {
        std::unique_lock<FastPthreadMutex> lck1(b->waiter_lock, std::defer_lock);
        std::unique_lock<FastPthreadMutex> lck2(m->waiter_lock, std::defer_lock);
        butil::double_lock(lck1, lck2);
        if (b->waiters.empty()) {
            return 0;
        }

        front = b->waiters.head()->value();
        front->RemoveFromList();
        front->container.store(NULL, butil::memory_order_relaxed);

        while (!b->waiters.empty()) {
            ButexWaiter* bw = b->waiters.head()->value();
            bw->RemoveFromList();
            m->waiters.Append(bw);
            bw->container.store(m, butil::memory_order_relaxed);
        }
    }

    if (front->tid == 0) {  // which is a pthread
        wakeup_pthread(static_cast<ButexPthreadWaiter*>(front));
        return 1;
    }
    ButexBthreadWaiter* bbw = static_cast<ButexBthreadWaiter*>(front);
    unsleep_if_necessary(bbw, get_global_timer_thread());
    auto g = is_same_tag(bbw->tag) ? tls_task_group : NULL;
    if (g) {
        TaskGroup::exchange(&g, bbw->task_meta);
    } else {
        bbw->control->choose_one_group(bbw->tag)->ready_to_run_remote(bbw->task_meta);
    }
    return 1;
}

// Callable from multiple threads, at most one thread may wake up the waiter.
static void erase_from_butex_and_wakeup(void* arg) {