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?

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?

• javascript
• node.js
• asynchronous

Share Improve this question Follow edited Dec 5, 2019 at 22:04 Max 1,06011 gold badge1212 silver badges2020 bronze badges asked Jan 18, 2016 at 22:13 MickeyThreeShedsMickeyThreeSheds 7322 silver badges99 bronze badges 3

• 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 Commented Jan 18, 2016 at 22:17
• You didn't even take a look at the docs, did you? Just use async.eachLimit. – Bergi Commented Jan 18, 2016 at 22:17
• Possible duplicate of Limiting asynchronous calls in Node.js – Andreas Commented Jan 18, 2016 at 22:17

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3 Answers 3

Sorted by: Reset to default 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');
        }
    }
);

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;
});

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.