CODEWITHSUNDEEP
javascriptnode.js
8bitAlex
8bitAlex

Reputation: 96

node.js setInterval not working in custom module

I am developing a web application in node.js to collect data from devices on a network using snmp. This is my first real encounter with node.js and javascript. In the app each device will be manipulated through a module I named SnmpMonitor.js. This module will maintain basic device data as well as the snmp and database connection.

One of the features of the app is the ability to constantly monitor data from smart metering devices. To do this I created the following code to start and stop the monitoring of the device. It uses setInterval to constantly send a snmp get request to the device. Then the event listener picks it up and will add the collected data to a database. Right now the listener just prints to show it was successful.

var dataOIDs = ["1.3.6.1.2.1.1.1.0","1.3.6.1.2.1.1.2.0"];
var intervalDuration = 500;
var monitorIntervalID;
var dataCollectionEvent = "dataCollectionComplete";
var emitter = events.EventEmitter(); // Uses native Event Module

//...

function startMonitor(){
    if(monitorIntervalID !== undefined){
        console.log("Device monitor has already started");
    } else {
        monitorIntervalID = setInterval(getSnmp,intervalDuration,dataOIDs,dataCollectionEvent);
        emitter.on(dataCollectionEvent,dataCallback);
    }
 }

function dataCallback(recievedData){
    // receivedData is returned from getSnmp completion event
    // TODO put data in database
    console.log("Event happened");
}

function stopMonitor(){
    if(monitorIntervalID !== undefined){
        clearInterval(monitorIntervalID);
        emitter.removeListener(dataCollectionEvent,dataCallback);
    } else {
        console.log("Must start collecting data before it can be stopped");
    }
}

//...

I also have a test file, test.js, that requires the module, starts monitoring, waits 10 seconds, then stops it.

var test = require("./SnmpMonitor");

test.startMonitor();
setTimeout(test.stopMonitor,10000);

My problem is that the setInterval function in startMonitor() is not being run. I have tried placing console.log("test"); before, inside, and after it to test it. The inside test output never executes. The monitorIntervalID variable is also returned as undefined. I have tested setInterval(function(){ console.log("test"); },500); in my test.js file and it runs fine with no issues. I feel like this is a noobie mistake but I just can't seem to figure out why it won't execute.

Here is a link to the entire module: SnmpMonitor.js

Upvotes: 2

Views: 1590

Answers (1)

8bitAlex
8bitAlex

Reputation: 96

I not sure exactly what was wrong but I got it to work by overhauling the whole class/module. I thought the way I had it was going to allow me to create new monitors objects but I was wrong. Instead I created two functions inside the monitor file that do the same thing. I changed the start function to the following.

SnmpMonitor.prototype.start = function() {
    var snmpSession = new SNMP(this.deviceInfo.ipaddress,this.emitter);
    var oids = this.deviceInfo.oids;
    var emit = this.emitter;
    var duration = this.intervalDuration;

    this.intervalID = setInterval(function(){
        snmpSession.get(dataCollectionEvent,emit,oids);
    },duration);
};

The setInterval function seems to work best when the callback function is set inside an anonymous function, even though technically you can pass it directly. Using the this. notation I created some class/module/function variables (whatever its called in js) that are in scope of the whole class. For some reason the variables accessed through this. do not work so well when directly in a function or expression so I created temp variables for them. In my other version all the variables were global and js doesn't seem to like that.

Upvotes: 1

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