Is it possible to limit async tasks in node?

Question

I have the following section of async code:

async.forEach(list, function(file, loopCallback) {
    console.log("file");
    loopCallback();
}, {
    console.log("all done!");
});

It prints the name of all my files in my list, great. Now, I want to limit the amount of files I am processing in parallel. What if I only want to handle one file at a time?

I have heard of async.ParallelLimit, and async.Queue, and would like to know how to adapt this code to fit one of them, specifically parallelLimit.

Any ideas?

so... you know that async has options that do what you want, but you want us to convert your code to one of those other options.. — Kevin B, Jan 18 '16 at 22:17
You didn't even take a look at [the docs](https://github.com/caolan/async#documentation), did you? Just use `async.eachLimit`. — Bergi, Jan 18 '16 at 22:17
Possible duplicate of [Limiting asynchronous calls in Node.js](http://stackoverflow.com/questions/9539886/limiting-asynchronous-calls-in-node-js) — Andreas, Jan 18 '16 at 22:17

score 5 · Answer 1 · answered Jan 18 '16 at 22:27

5

I think what you need is eachLimit, not parallelLimit. Here is an example:

async.each(
    list,
    1, // limit
    function(file, callback) {
        console.log('Processing file ' + file);
        callback();
    },
    function(err){
        if( err ) {
          console.log('Failed to process');
        } else {
          console.log('All files have been processed successfully');
        }
    }
);

answered Jan 18 '16 at 22:27

Ionut

1,729
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Thanks! that was perfect! – MickeyThreeSheds Jan 20 '16 at 22:54
2

@MickeyThreeSheds you are supposed to upvote when someone provides a good answer :) At this point, I upvoted for you. – Alexander Mills Nov 08 '16 at 19:23

score 0 · Answer 2 · answered Jan 18 '16 at 22:19

0

You could try using (every) instead of foreach

var count = 0;
var totalcount = 5;
async.every(function() {
// Do something.
count++;
if (count == 5)
   return false;
   else return true;
});

answered Jan 18 '16 at 22:19

Rosenumber14

165
12

score 0 · Answer 3 · answered Jan 18 '16 at 22:25

0

I think that async.mapLimit is what you need:

async.mapLimit([1,2,3,4,5], 3, function(value, loopCallback) {
    // will process by 3 items at time
    console.log(value);
    loopCallback(value);
}

It is mentioned in the map description.

answered Jan 18 '16 at 22:25

Borys Serebrov

15,636
2
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Is it possible to limit async tasks in node?

3 Answers3