pubsub如何知道某个时间点发布了多少条消息?

在此处发布消息的代码:

Code for publishing the messages here:

async function publishMessage(topicName) {
  console.log(`[${new Date().toISOString()}] publishing messages`);
  const pubsub = new PubSub({ projectId: PUBSUB_PROJECT_ID });
  const topic = pubsub.topic(topicName, {
    batching: {
      maxMessages: 10,
      maxMilliseconds: 10 * 1000,
    },
  });

  const n = 5;
  const dataBufs: Buffer[] = [];
  for (let i = 0; i < n; i++) {
    const data = `message payload ${i}`;
    const dataBuffer = Buffer.from(data);
    dataBufs.push(dataBuffer);
  }

  const results = await Promise.all(
    dataBufs.map((dataBuf, idx) =>
      topic.publish(dataBuf).then((messageId) => {
        console.log(`[${new Date().toISOString()}] Message ${messageId} published. index: ${idx}`);
        return messageId;
      })
    )
  );
  console.log('results:', results.toString());
}

如您所见，我将发布5条消息.发布时间是await Promise.all(...)，对于用户来说，这时我们可以说发送消息，但是对于pubsub库内部而言，可能不是.我将maxMessages设置为10，因此pubsub将等待10秒(maxMilliseconds)，然后发布这5条消息.

As you can see, I am going to publish 5 messages. The time to publish is await Promise.all(...), I mean, for users, We can say send messages at this moment, but for internal of pubsub library maybe not. I set maxMessages to 10, so pubsub will wait for 10 seconds(maxMilliseconds), then publish these 5 messages.

抽烟结果符合我的期望:

The exuection result meets my expectations:

[2020-05-05T09:53:32.078Z] publishing messages
[2020-05-05T09:53:42.209Z] Message 36854 published. index: 0
[2020-05-05T09:53:42.209Z] Message 36855 published. index: 1
[2020-05-05T09:53:42.209Z] Message 36856 published. index: 2
[2020-05-05T09:53:42.209Z] Message 36857 published. index: 3
[2020-05-05T09:53:42.209Z] Message 36858 published. index: 4
results: 36854,36855,36856,36857,36858

实际上，我认为topic.publish不会直接调用远程pubsub服务，而是将消息推送到内存队列中.而且有一个窗口时间可以计算邮件的数量，可能是打勾或类似的时间:

In fact, I think topic.publish does not directly call the remote pubsub service, but pushes the message into the memory queue. And there is a window time to calculate the count of the messages, maybe in a tick or something like:

// internal logic of @google/pubsub library
setTimeout(() => {
  // if user messages to be published gte maxMessages, then, publish them immediately
  if(getLength(messageQueue) >= maxMessages) {
    callRemotePubsubService(messageQueue)
  }
}, /* window time = */ 100);

还是使用setImmediate()，process.nextTick()?