void io_uring_context::update_timers()

in source/linux/io_uring_context.cpp [695:766]

• 52 lines of code
• 14 McCabe index (conditional complexity)

void io_uring_context::update_timers() noexcept {
  LOG("update_timers()");

  // Reap any elapsed timers.
  if (!timers_.empty()) {
    time_point now = monotonic_clock::now();
    while (!timers_.empty() && timers_.top()->dueTime_ <= now) {
      schedule_at_operation* item = timers_.pop();

      LOGX("dequeued elapsed timer %p\n", (void*)item);

      if (item->canBeCancelled_) {
        auto oldState = item->state_.fetch_add(
            schedule_at_operation::timer_elapsed_flag,
            std::memory_order_acq_rel);
        if ((oldState & schedule_at_operation::cancel_pending_flag) != 0) {
          LOGX("timer already cancelled\n");

          // Timer has been cancelled by a remote thread.
          // The other thread is responsible for enqueueing is operation onto
          // the remoteQueue_.
          continue;
        }
      }

      // Otherwise, we are responsible for enqueuing the timer onto the
      // ready-to-run queue.
      schedule_local(item);
    }
  }

  // Check if we need to cancel or start some new OS timers.
  if (timers_.empty()) {
    if (currentDueTime_.has_value()) {
      LOG("no more schedule_at requests, cancelling timer");

      // Cancel the outstanding timer.
      if (try_submit_timer_io_cancel()) {
        currentDueTime_.reset();
        timersAreDirty_ = false;
      }
    }
  } else {
    const auto earliestDueTime = timers_.top()->dueTime_;

    if (currentDueTime_) {
      constexpr auto threshold = std::chrono::microseconds(1);
      if (earliestDueTime < (*currentDueTime_ - threshold)) {
        LOG("active timer, need to cancel and submit an earlier one");

        // An earlier time has been scheduled.
        // Cancel the old timer before submitting a new one.
        if (try_submit_timer_io_cancel()) {
          currentDueTime_.reset();
          if (try_submit_timer_io(earliestDueTime)) {
            currentDueTime_ = earliestDueTime;
            timersAreDirty_ = false;
          }
        }
      } else {
        timersAreDirty_ = false;
      }
    } else {
      // No active timer, submit a new timer
      LOG("no active timer, trying to submit a new one");
      if (try_submit_timer_io(earliestDueTime)) {
        currentDueTime_ = earliestDueTime;
        timersAreDirty_ = false;
      }
    }
  }
}