如何等待多个异步函数完成？

Question

I've devloped a class that has few function that run and update data inside of a database. I want to run 10 threads of my class at a time , and start new run everytime one of them is done (so there always be 10 operations running or less) How can I accomplish it?

Example of the code:

const classobj = require("data.js");
    let class1 = new Data();
    let class2 = new Data();
    ... //(8 more)

    class1.run();
    class2.run();
    ... // (8 more)

    // one one of the class1-10 is done i want it to start again

Thank you!

Answer 1

You can make the function call itself when the promise resolves

 const randomDelay = () => (Math.floor(Math.random() * 5) + 2) * 1000 const fakePromise = id => new Promise(res => setTimeout(() => { console.log(`class ${id} finished work`) res() }, randomDelay())) class MyClass { constructor(id) { this.id = id } run = () => { console.log(`class ${this.id} starting work`) fakePromise(this.id).then(this.run) } } // create 3 instances and call .run() on every one [...new Array(3)] .map((_, i) => new MyClass(i + 1)) .forEach(classInstance => { classInstance.run() })

Answer 2

If the Data.run function returns a Promise, you could do something like this:

const classobj = require("data.js");

const restartingPromise = (promise) => {
  promise().then(() => {
    restartingPromise();
  });
};

let class1 = new Data();
let class2 = new Data();
... //(8 more)

restartingPromise(class1.run);
restartingPromise(class2.run);
...