如何在 nodejs 应用程序中使用 async-lock 来锁定 /get 资源功能

Question

我一直在尝试使用 async-lock npm 模块来锁定 /get 资源执行。

import cors from "cors";
import express from "express";
import AsyncLock from "async-lock";
import _ from "lodash";

const app = express();
const port = process.env.port || 3001;

app.use(cors());
app.use(express.json());

let synchonizationKey: string = "";
let lock = new AsyncLock();

app.get("/pckg", (req, res) => {
  let id = _.uniqueId();
  console.log("--------------Request ", id, " arrived");

  lock.acquire(
    synchonizationKey,
    function () {
      console.log("--------------Request ", id, " lockAquired");

      setTimeout(function () {
        console.log("--------------Request ", id, " Done");
      }, 3000);
    },
    function (err, ret) {
      console.log("--------------Request ", id, " lockReleased");
      res.send({ id: id });
    },
    {}
  );
});

app.listen(port, () => console.log("Running on port#" + port));

输出：我从浏览器发出的 4 个获取请求。

--------------Request  1  arrived
--------------Request  1  lockAquired
--------------Request  1  lockReleased
--------------Request  2  arrived
--------------Request  2  lockAquired
--------------Request  2  lockReleased
--------------Request  3  arrived
--------------Request  3  lockAquired
--------------Request  3  lockReleased
--------------Request  4  arrived
--------------Request  4  lockAquired
--------------Request  4  lockReleased
--------------Request  1  Done
--------------Request  2  Done
--------------Request  3  Done
--------------Request  4  Done

我期待得到与question 中回答的类似行的结果

看起来，一旦回调中的所有同步部分执行完毕，锁就会被释放。

有人可以帮我解决这个问题吗？

Answer 1

如果您查看async-lock 包的docs，您会注意到acquire 函数具有以下签名

acquire(
  key,
  executeFunction,
  callbackFunction,
  options);

executeFunction 本身有签名的地方

function(done) {...}

而done是一个回调函数，用于在你的临界区工作完成后调用callbackFunction，并且可以释放锁。您省略了 done 参数，因此没有手动调用 callbackFunction。因此，一旦executeFunction 完成，就会调用它（因此释放锁）。而且由于你的执行函数中的setTimeout当然也是异步的，它不会延迟executionFunction。

所以正确的使用方法，如下

lock.acquire(
  synchonizationKey,
  function (done) {  // <----- new parameter for the function
    console.log("--------------Request ", id, " lockAquired");

    setTimeout(function () {
      console.log("--------------Request ", id, " Done");
      done();  // <---- call the callback, once the lock can be released 
    }, 3000);
  },
  function (err, ret) {
    console.log("--------------Request ", id, " lockReleased");
    res.send({ id: id });
  },
  {});

这导致以下输出

--------------Request  1  arrived
--------------Request  1  lockAquired
--------------Request  2  arrived
--------------Request  3  arrived
--------------Request  4  arrived
--------------Request  1  Done
--------------Request  1  lockReleased
--------------Request  2  lockAquired
--------------Request  2  Done
--------------Request  2  lockReleased
--------------Request  3  lockAquired
--------------Request  3  Done
--------------Request  3  lockReleased
--------------Request  4  lockAquired
--------------Request  4  Done
--------------Request  4  lockReleased