CODEWITHSUNDEEP
javascriptnode.jsasynchronousnpmsynchronization
E.S.
E.S.

Reputation: 2841

How to ensure blocking during a loop in Node.JS

Although I usually enjoy the callback-soup that is Node.JS, I found that a certain part of my code needs to be run in a blocking manner because of an SQLite issue. (Yes, I know I could try and address the SQLite part, it actually makes more sense to ensure blocking.)

I like using the async module, and though I have a feeling that module has a feature which can be used here, I can't seem to find it. Or, maybe there is a better module out there. Anyway, without further ado:

func = function(callback) {
    let i = 0;
    arr.forEach(val => {
        if (val.trim().length > 0) {
            console.log(`Starting for user ${val}.`);
            let mylc = new lcapp(val);
            ////// TODO this needs to be made sycnronous. /////
            async.series({
                getMyDetails: callback => getMyDetails(mylc, callback)
            }, (err, results) => handleResults(err, results, mylc, callback));
            /////////////
        }
    });
};

The section of code surrounded by //// I would like to block until the handleResults function returns. I understand it will require reprogramming the callback in handleResults, or maybe I need to write a parent function around func but I'd like to see if StackOverflow people have some good ideas.

Upvotes: 1

Views: 393

Answers (2)

Chris
Chris

Reputation: 2806

You could turn it into a function that recursively calls itself when the handleResults callback is hit.

You can do this by following the example below.

fun()

function fun() {
  console.time("fun")
  var arr = [1, 2, 3, 4, 5]
  var i = arr.length - 1;
  doStuff(doStuffCallback)

  function doStuffCallback() {
    if (i > 0) {
      i--
      doStuff(doStuffCallback)
    } else {
      console.timeEnd("fun")
    }
  }

  function doStuff(callback) {
    setTimeout(function() {
      logIt()
      callback()
    }, 25)
  }

  function logIt() {
    console.log(arr[i])
  }
}

// Output:
// 5
// 4
// 3
// 2
// 1
// fun: about 160ms

PS: I'm assuming you only need to be synchronous within this method and the loop therein. Other code might still be running elsewhere in your application while this runs.

Upvotes: 1

idbehold
idbehold

Reputation: 17168

Yes, I know I could try and address the SQLite part, it actually makes more sense to ensure blocking.

No it doesn't, because you can't. You need to resolve whatever issue you have with it being async because there is no way to turn asynchronous code into synchronous code.

Upvotes: 0

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