Call variable number of functions in parallel?

Question

Using async.parallel or custom control flow,

arr = [1, 2, 3, 4, 5, 3, 2, 3, 4, 5] //arr could be any length

get_something = function(num, cb){
  async_io(num, function (err, results){
        cb()
  });

}

I want to run get_something() on each member of the array in "parallel". When they're all finished I'd like the callback to get called with the results.

Really in parallel ? Or just the external asynchronous part in parallel ? — Denys Séguret
– Denys Séguret, Commented Sep 3, 2013 at 15:47
and does get_something takes a callback and call it ? If not it will be hard... — Denys Séguret
– Denys Séguret, Commented Sep 3, 2013 at 15:48

Denys Séguret · Accepted Answer · 2013-09-03 16:06:34Z

1

Without async :

var n = arr.length, results = new Array(n), oneIsDone = function(index, result){
   results[index] = result;
   if (--n===0) callback(results);
}
arr.forEach(function(val i){ 
    get_something(val, function(result){
       oneIsDone(i, result);
    });
});

With async :

Using async supposes your asynchronous function accepts a callback returning an error as first argument and the result as second, just like your final callback :

async.parallel(arr, get_something, callback);

If your functions don't follow this norm, you'll have to make some ugly wrappings.

edited Sep 3, 2013 at 16:06

answered Sep 3, 2013 at 15:49

Denys Séguret

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3 Comments

boom Over a year ago

Trying to get the results passed into the callback sorted by index. results = [{results from 0}, {results from 1}] Similar to how async.parallel works.

Denys Séguret Over a year ago

Is result given to the callback you give to get_something ?

boom Over a year ago

so then get_something should get passed arr[i] not i? Is i the index or the value?

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