Function wait_for_butex

src/bthread/butex.cpp:549–610

};

void wait_for_butex(void* arg) {
    auto args = static_cast<WaitForButexArgs*>(arg);
    ButexBthreadWaiter* const bw = args->bw;
    Butex* const b = bw->initial_butex;
    // 1: waiter with timeout should have waiter_state == WAITER_STATE_READY
    //    before they're queued, otherwise the waiter is already timedout
    //    and removed by TimerThread, in which case we should stop queueing.
    //
    // Visibility of waiter_state:
    //    [bthread]                         [TimerThread]
    //    waiter_state = TIMED
    //    tt_lock { add task }
    //                                      tt_lock { get task }
    //                                      waiter_lock { waiter_state=TIMEDOUT }
    //    waiter_lock { use waiter_state }
    // tt_lock represents TimerThread::_mutex. Visibility of waiter_state is
    // sequenced by two locks, both threads are guaranteed to see the correct
    // value.
    {
        BAIDU_SCOPED_LOCK(b->waiter_lock);
        if (b->value.load(butil::memory_order_relaxed) != bw->expected_value) {
            bw->waiter_state = WAITER_STATE_UNMATCHEDVALUE;
        } else if (bw->waiter_state == WAITER_STATE_READY/*1*/ &&
                   !bw->task_meta->interrupted) {
            if (args->prepend) {
                b->waiters.Prepend(bw);
            } else {
                b->waiters.Append(bw);
            }
            bw->container.store(b, butil::memory_order_relaxed);
#ifdef BRPC_BTHREAD_TRACER
            bw->control->_task_tracer.set_status(TASK_STATUS_SUSPENDED, bw->task_meta);
#endif // BRPC_BTHREAD_TRACER
            if (bw->abstime != NULL) {
                bw->sleep_id = get_global_timer_thread()->schedule(
                    erase_from_butex_and_wakeup, bw, *bw->abstime);
                if (!bw->sleep_id) {  // TimerThread stopped.
                    errno = ESTOP;
                    erase_from_butex_and_wakeup(bw);
                }
            }
            return;
        }
    }
    
    // b->container is NULL which makes erase_from_butex_and_wakeup() and
    // TaskGroup::interrupt() no-op, there's no race between following code and
    // the two functions. The on-stack ButexBthreadWaiter is safe to use and
    // bw->waiter_state will not change again.
    // unsleep_if_necessary(bw, get_global_timer_thread());
    tls_task_group->ready_to_run(bw->task_meta);
    // FIXME: jump back to original thread is buggy.
    
    // // Value unmatched or waiter is already woken up by TimerThread, jump
    // // back to original bthread.
    // TaskGroup* g = tls_task_group;
    // ReadyToRunArgs args = { g->current_tid(), false };
    // g->set_remained(TaskGroup::ready_to_run_in_worker, &args);