I have a function with a promises which must be executed n times with different params each time. I want to chain the promises in a way that the script is always working on 3-4 promises at the time.
I made it with promise.all, this executes 3 concurrently and when all the promises resolves it goes on with the next 3.
How to make it work that when one of 3 resolves it starts immediatly with another but always working on max 3 at the time?
for( var i = 0; i < tasks.length; i++){
if( i > 0 && i%3 == 0 ){
await Promise.all([
doTaskFunction(tasks[i]),
doTaskFunction(tasks[i-1]),
doTaskFunction(tasks[i-2]),
]);
}
}
You can achieve this fairly easy using es6-promise-pool:
const tasks = [
(param) => new Promise(function(resolve, reject) {
setTimeout(resolve, 2000, 'foo');
}),
() => new Promise(function(resolve, reject) {
setTimeout(resolve, 2000, 'foo');
}),
() => new Promise(function(resolve, reject) {
setTimeout(resolve, 2000, 'foo');
}),
() => Promise.resolve(1),
() => Promise.resolve(2),
() => Promise.resolve(3)
];
let count = 1;
const promiseProducer = () => {
while(tasks.length) {
console.log('processing ' + count++);
const task = tasks.shift();
return task(); // optionally you could pass a parameter here
}
return null;
}
const pool = new PromisePool(promiseProducer, 3); // concurrent Promises set to 3
const poolPromise = pool.start();
poolPromise.then(() => { console.log('done!'); })
<script src="https://cdn.jsdelivr.net/npm/[email protected]/es6-promise-pool.min.js"></script>