function getResource(uri, data_callback, error_callback, timeout) {
    var tryAgain = function () {
      getResource(uri, data_callback, error_callback, timeout);
    }
    //var r = (XMLHttpRequest)?new XMLHttpRequest():new ActiveXObject('Microsoft.XMLHTTP');
    var r = new XMLHttpRequest();
	var timer = setTimeout(
        function() {
            r.abort();
            r.onreadystatechange = null;
            setTimeout(tryAgain, timeout);
        },
        timeout);
    r.open("GET", uri, true);
    r.onreadystatechange = function() {
        if (r.readyState != 4) {
            return;
        }
        clearTimeout(timer);  // readyState==4, borramos timer
        if (r.status==200) {  // "OK status"
              data_callback(r.responseText);
        }
        else if (r.status==304) {
            // "Not Modified": No modificamos la salida
        }
        else if (r.status >= 400 && r.status < 500) {
            // Posible error, posible URI erronea
            error_callback(r)
        }
        else if (r.status >= 500 && r.status < 600) {
            // Server error, volvemos a lanzar con un poco de demora
            setTimeout(tryAgain, timeout);
        }
        else {
            error_callback(r);
        }
    }
    r.send(null);
    return r;
}



var other_data = null;
function processData(this_data) {
    var delay = 1000;     // Esperamos 1 segundo
    if (other_data == null) {
        setTimeout(function() { processData(this_data); }, delay);
        return;
    }
    // Tenemos this_data y other_data
    displayThisAndThat(this_data, other_data);
    // Reseteamos other_data, ya la hemos usado
    other_data = null;
}