High CPU load when using XMLHttpRequest

[PhilipT]

Hello!

In my QML application I am using multiple instances of a custom Item, which uses XMLHttpRequest to get and put data (Strings) from and to a REST API. The App is working fine and the CPU load rarely passes the 10% mark. However, since I added the REST interface the CPU load increased dramatically, somtimes even over 90%..

The QML Item:

import QtQuick 2.0

Item {
    id:ohi

    property string itemname: ""
    property int port: 8080
    property var state
    property var lastReceivedJson
    property var step
    property var min
    property var max
    property var inc_val
    property var dec_val
    property bool polling: false
    property string ip_addr: (Qt.platform.os == "windows") ? "192.168.2.55" : "127.0.0.1"
    property bool receivedData: false
    property var json
    onJsonChanged: {
        //lagFix.stop();
        if(json.state !== undefined) {
            receivedData = true;
        } else {
            receivedData = false;
        }
        lastReceivedJson = json;
        state = json.state;
    }

    function mylog( val ) {
        console.log( val );
    }

    function setValue( value ) {
        var url = "http://" + ip_addr + ":" + String(port) + "/rest/items/" + itemname;
        setWorker.sendMessage( {"url": url, "value": value } );
    }

    Timer {
        id: updateTimer
        interval: 5000
        running: polling; repeat: true
        onTriggered: {
            var url = "http://" + ip_addr + ":" + String(port) + "/rest/items/" + itemname;
            getWorker.sendMessage( {"url": url, "parameter": null } );
        }
    }

    WorkerScript {
        id: getWorker
        source: "workerscript_get.js"

        onMessage: {
            json = messageObject.json;
        }
    }

    WorkerScript {
        id: setWorker
        source: "workerscript_post.js"
    }
}

The JS for the WorkerScripts (workerscript_get):

function request(url, arguments, callback) {
    var myurl = url;
    // todo: add arguments
    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.onreadystatechange = function() {
            if(xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {
                callback(xhr);
            }
    }
    xhr.send();
}

WorkerScript.onMessage = function(message) {
    request(message.url, message.parameter, mycallback );
}

function mycallback( o ) {
    var json = JSON.parse(o.responseText);
    WorkerScript.sendMessage({ json: json });
}

and workerscript_post:

function sendVal(url, value) {
    var myurl = url;
    // todo: add arguments
    var xhr = new XMLHttpRequest();
    xhr.open('POST', url, true);
    xhr.onreadystatechange = function() {
            if(xhr.readyState === XMLHttpRequest.DONE && xhr.status === 200) {}
            else { console.log("Error sending state " + value + " !!"); }
    }
    xhr.send( value );
}

WorkerScript.onMessage = function( message ) {
    sendVal(message.url, message.value);
}

Could anyone lead me to the reason of the high CPU load?

Thanks a lot!!

HW: Allwinner A20