How to correctly perform async I/O in map iterator in node.js?

Question

How to correctly perform async I/O in map iterator in node.js?

Possible Duplicate:
Cannot use “map” function within async module

I've got a problem like this:

    var paths = ['path1', 'path2', 'path3', ...]; //Some arbitrary array of paths

    var results; //I need to collect an array of results collected from these paths

results = paths.map(function(path){
  var tempResult;

  GetData(path, function(data){ //Third-party async I/O function which reads data from path
    tempResult = data;
  });

  return tempResult;
});

console.log(results); //returns something like [nothing, nothing, nothing, ...]

I can imagine why it happens (return tempResult fires before the async function returned any data - it's slow after all), but can't quite see how to make it right.

My guess is async.map might help, but I fail to see how right away.

Maybe someone more experienced in asynchronous programming might explain the way?

node.js
asynchronous
map

Answer 1

You could try something like:

async.map(paths,function(path,callback){
    GetData(path,function(data){ callback(null,data); });
},function(error,results){
    if(error){ console.log('Error!'); return; }
    console.log(results);
    // do stuff with results
});

As you can see, you'll need to shift the code that processes the results into the function to be passed into async.map.