CODEWITHSUNDEEP
node.jsasynchronous
user1598585
user1598585

Reputation:

Asynchronous wait for an condition to be met

In my code I have three variables whose value depend on an external function call, they can be set to true in any moment and in any order, so, they are more like flags.

I need a function to be only once these three variables are set to true.

How can I perform a wait for these three variables to be true, without blocking my server, in an asynchronous way?

(I do not want to be refered to external libraries)

Upvotes: 3

Views: 11846

Answers (3)

Andi Giga
Andi Giga

Reputation: 4162

It can be also done with event emitter. I n the example I watch a folder and wait for the following file. One could also use setTimeout for demo purposes.

const counterEmitter = new EventEmitter();

// wait for the second file before processing the first file
let globalCounter = 0;
chokidar.watch(process.env.WATCH).on('add', (filePath) => {

     globalCounter++;
     const counter = globalCounter;        
     counterEmitter.once('counterEvent', (counterEvent) => {
         console.log('counterEvent', counterEvent);
         if (counter < counterEvent) {
              console.log("I waited", counter)
         }
     });
     counterEmitter.emit('counterEvent', globalCounter)
     ...

Upvotes: 0

Anatoliy
Anatoliy

Reputation: 30073

If you control state of these variables - why not trigger some event when you set this variables? Even better - have some object that incapsulates this logic. Something like:

function StateChecker(callback) {
    var obj = this;
    ['a', 'b', 'c'].forEach(function (variable) {
        Object.defineProperty(obj, variable, {
            get: function () { return a; }
            set: function (v) { values[variable] = v; check(); }
        });
    });
    function check() {
        if (a && b && c) callback();
    }
}

var checker = new StateChecker(function () {
    console.log('all true');
});

checker.a = true;
checker.b = true;
checker.c = true;
> 'all true'

Upvotes: 2

Julian Lannigan
Julian Lannigan

Reputation: 6522

I generally like to use the async library for doing things like this, but since you don't want to be referred to external libraries for this. I will write a simple function that checks it at an interval to see if the variables have been set.

Interval Check Method

var _flagCheck = setInterval(function() {
    if (flag1 === true && flag2 === true && flag3 === true) {
        clearInterval(_flagCheck);
        theCallback(); // the function to run once all flags are true
    }
}, 100); // interval set at 100 milliseconds

Async Library Parallel Method

var async = require('async');

async.parallel([
    function(callback) {
        // handle flag 1 processing
        callback(null);
    },

    function(callback) {
        // handle flag 2 processing
        callback(null);
    },

    function(callback) {
        // handle flag 3 processing
        callback(null);
    },
], function(err) {
    // all tasks have completed, run any post-processing.
});

Upvotes: 8

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