javascript - 等待永远不会解决，之后的下一行从未执行

Question

我正在使用 async await 并且我的 await 从未解析，所以下一行根本没有执行。我的意思是这一行:

result = await IndexingStatusResult(req, res);

在下面的代码中:

router.post(
  "/api/result-store/v1/indexing-analyzer/:searchID/:id",
  async (req, res) => {
    console.log("Indexing started");
    var hrstart = process.hrtime();
    let result = null;

    result = await IndexingStatusResult(req, res);
    console.log("result is: ", result.data);
    hrend = process.hrtime(hrstart);
    console.info("Execution time (hr): %ds %dms", hrend[0], hrend[1] / 1000000);

    res.status(200).send({
      indexingTimeSec: hrend[0],
      indexingTimeMillSec: hrend[1] / 1000000
    });
  }
);

但是正如您在 IndexingStatusResult 中看到的那样，当一切都完成时我返回一个 promise :

const IndexingStatusResult = async (req, res) => {
  const docID = parseInt(req.params.id) * 1000;
  const dbName = "test_" + req.params.searchID;
  let result = null;
  try {
    result = await axios(
      `${params.HOST_NAME_WITH_PROTOCOL}/${dbName}/_design/searchAll/_search_info/searchAll`
    );
    result = result.data;
    console.log(
      "Number of docs indexed:",
      result.search_index.doc_count,
      "Total Docs needs to be indexed:",
      docID
    );
  } catch (e) {
    console.log(e);
  }
  console.log(`result returned is : ${JSON.stringify(result)}`);
  if (!result || parseInt(result.search_index.doc_count) < docID) {
return Promise.resolve(
  setTimeout(() => {
    console.log("WWWWWAAAAIIIIIITING");
    IndexingStatusResult(req, res);
  }, 5000)
);
  } else {
    console.log("YAAAAAAYYYYYYYYYYYYY");
    return Promise.resolve(result);
  }
};

这是我看到的:

Example app listening on port 3005!
Indexing started
Number of docs indexed: 0 Total Docs needs to be indexed: 5000
result returned is : {"name":"_design/searchAll/searchAll","search_index":{"pending_seq":0,"doc_del_count":0,"doc_count":0,"disk_size":0,"committed_seq":0}}
result is:  undefined
Execution time (hr): 0s 314.964402ms
WWWWWAAAAIIIIIITING
Number of docs indexed: 0 Total Docs needs to be indexed: 5000
result returned is : {"name":"_design/searchAll/searchAll","search_index":{"pending_seq":0,"doc_del_count":0,"doc_count":0,"disk_size":0,"committed_seq":0}}
WWWWWAAAAIIIIIITING
Number of docs indexed: 5001 Total Docs needs to be indexed: 5000
result returned is : {"name":"_design/searchAll/searchAll","search_index":{"pending_seq":5001,"doc_del_count":0,"doc_count":5001,"disk_size":797698,"committed_seq":0}}
YAAAAAAYYYYYYYYYYYYY

所以下面这行永远不会被执行:

console.log("result is: ", result.data);

我做错了什么吗？

Answer 1

几个问题:

• 你写“但是正如你在IndexingStatusResult中看到的那样，当一切都完成时，我会做出 promise ”。此声明显示了一个误解:An async函数返回一个 promise 同步，而不是在“一切”(异步)完成时。
• “我的 await 永远不会解决 [s]”:它会解决，而且比您想象的要快。声明console.log("result is: ", result.date) 确实被执行，但它是触发错误的那个。
• 来电setTimeout在IndexingStatusResult不会延迟它返回的 promise 的解决时刻。在调用 setTimeout 之后您什么都不做(在编辑中，您在此处显式返回)， promise 以 undefined 实现. 现阶段setTimeout回调尚未执行。 undefined分辨率值解释了您遇到的错误。
• 还应注意，您已经拥有 result = result.data ，所以即使您将其作为分辨率值返回，result.data不会存在。
• 而不是 setTimeout打电话，做await delay(5000) , 其中delay返回超时后解决的 promise 。
• 在async函数，您不需要将返回值包装为 promise 。如上所述，promise 对象已经返回，实际的 return语句应指示该 promise 现在应解决的值。

所以(没有测试)，我会说这段代码会做得更好:

router.post(
  "/api/result-store/v1/indexing-analyzer/:searchID/:id",
  async (req, res) => {
    console.log("Indexing started");
    var hrstart = process.hrtime();
    let result = null;

    result = await IndexingStatusResult(req, res);
    console.log("result is: ", result); // not .data
    hrend = process.hrtime(hrstart);
    console.info("Execution time (hr): %ds %dms", hrend[0], hrend[1] / 1000000);

    res.status(200).send({
      indexingTimeSec: hrend[0],
      indexingTimeMillSec: hrend[1] / 1000000
    });
  }
);

// Helper function that's very useful in async functions:
const delay = ms => new Promise(resolve => setTimeout(resolve, ms));

const IndexingStatusResult = async (req, res) => {
  const docID = parseInt(req.params.id) * 1000;
  const dbName = "test_" + req.params.searchID;
  let result = null;
  while (true) {
    try {
      result = await axios(
        `${params.HOST_NAME_WITH_PROTOCOL}/${dbName}/_design/searchAll/_search_info/searchAll`
      );
      result = result.data;
      console.log(
         "Number of docs indexed:",
        result.search_index.doc_count,
        "Total Docs needs to be indexed:",
        docID
      );
    } catch (e) {
      console.log(e);
      return e; // ?? determine what you want to happen...
    } 
    console.log(`result returned is : ${JSON.stringify(result)}`);
    if (result && parseInt(result.search_index.doc_count) >= docID) break;
    await delay(5000); // delay and keep looping
  }
  console.log("YAAAAAAYYYYYYYYYYYYY");
  return result;
};