Develop Reference

Ajax calls DURING another Ajax call to receive server's task calculation status and display it to the client as a progression bar

I'm trying to figure out if there's any chance to receive the status of completion of a task (triggered via an ajax call), via multiple (time intervalled) ajax calls.
Basically, during the execution of something that could take long, I want to populate some variable and return it's value when asked.
Server code looks like this:
function setTask($total,$current){
$this->task['total'] = $total;
$this->task['current'] = $current;
}
function setEmptyTask(){
$this->task = [];
}
function getTaskPercentage(){
return ($this->task['current'] * 100) / $this->task['total'];
}
function actionGetTask(){
if (Yii::$app->request->isAjax) {
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
return [
'percentage' => $this->getTaskPercentage(),
];
}
}
Let's say I'm in a for loop, and I know how many times I iterate over:
function actionExportAll(){
$size = sizeof($array);
$c = 0;
foreach($array as $a){
// do something that takes relatively long
$this->setTask($size,$c++);
}
}
While in the client side i have this:
function exportAll(){
var intervalId = setInterval(function(){
$.ajax({
url: '/get-task',
type: 'post',
success: function(data){
console.log(data);
}
});
},3000);
$.ajax({
url: '/export-all',
type: 'post',
success: function(data){
clearInterval(intervalId); // cancel setInterval
// ..
}
});
}
This looks like it could work, besides the fact that ajax calls done in the setInterval function are completed after "export-all" is done and goes in the success callback.
There's surely something that I'm missing in this logic.
Thanks

The problem is probably in sessions.
Let's take a look what is going on.
The request to /export-all is send by browser.
App on server calls session_start() that opens the session file and locks access to it.
The app begins the expensive operations.
In browser the set interval passes and browser send request to /get-task.
App on server tries to handle the /get-task request and calls session_start(). It is blocked and has to wait for /export-all request to finish.
The expensive operations of /export-all are finished and the response is send to browser.
The session file is unlocked and /get-task request can finally continue past session_start(). Meanwhile browser have recieved /export-all response and executes the success callback for it.
The /get-task request is finished and response is send to browser.
The browser recieves /get-task response and executes its success callback.
The best way to deal with it is avoid running the expensive tasks directly from requests executed by user's browser.
Your export-all action should only plan the task for execution. Then the task itself can be executed by some cron action or some worker in background. And the /get-task can check its progress and trigger the final actions when the task is finished.
You should take look at yiisoft/yii2-queue extension. This extension allows you to create jobs, enqueue them and run the jobs from queue by cron task or by running a daemon that will listen for tasks and execute them as they come.

Without trying to dive into your code, which I don't have time to do, I'll say that the essential process looks like this:
Your first AJAX call is "to schedule the unit of work ... somehow." The result of this call is to indicate success and to hand back some kind of nonce, or token, which uniquely identifies the request. This does not necessarily indicate that processing has begun, only that the request to start it has been accepted.
Your next calls request "progress," and provide the nonce given in step #1 as the means to refer to it. The immediate response is the status at this time.
Presumably, you also have some kind of call to retrieve (and remove) the completed request. The same nonce is once again used to refer to it. The immediate response is that the results are returned to you and the nonce is cancelled.
Obviously, you must have some client-side way to remember the nonce(s). "Sessions" are the most-common way to do that. "Local storage," in a suitably-recent web browser, can also be used.
Also note ... as an important clarification ... that the title to your post does not match what's happening: one AJAX call isn't happening "during" another AJAX call. All of the AJAX calls return immediately. But, all of them refer (by means of nonces) to a long-running unit of work that is being carried out by some other appropriate means.
(By the way, there are many existing "workflow managers" and "batch processing systems" out there, open-source on Github, Sourceforge, and other such places. Be sure that you're not re-inventing what someone else has already perfected! "Actum Ne Agas: Do Not Do A Thing Already Done." Take a few minutes to look around and see if there's something already out there that you can just steal.)

So basically I found the solution for this very problem by myself.
What you need to do is to replace the above server side's code into this:
function setTask($total,$current){
$_SESSION['task']['total'] = $total;
$_SESSION['task']['current'] = $current;
session_write_close();
}
function setEmptyTask(){
$_SESSION['task'] = [];
session_write_close();
}
function getTaskPercentage(){
return ($_SESSION['task']['current'] * 100) / $_SESSION['task']['total'];
}
function actionGetTask(){
if (Yii::$app->request->isAjax) {
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
return [
'percentage' => $this->getTaskPercentage(),
];
}
}
This works, but I'm not completely sure if is a good practice.
From what I can tell, it seems like it frees access to the $_SESSION variable and makes it readable by another session (ence my actionGetTask()) during the execution of the actionExportAll() session.
Maybe somebody could integrate this answer and tell more about it.
Thanks for the answers, I will certainly dig more in those approaches and maybe try to make this same task in a better, more elegant and logic way.

How to handle multiple requests being sent in JavaScript?

Working on a platform, to enable auto-ticketing functionality. For which a REST API request is used for ticket creation. Unfortunately, there are 2 requests popping simultaneously, which results in creating duplicated tickets.
How to handle such case and send only one of these requests?
Tried adding the 2nd request in the response callback of the first, though this does not seem to work.
if (flag == 1){
logger.debug("Node-down alarm-Request raised - +sitn_id);
clearTimeout(mouseoverTimer);
mouseoverTimer = setTimeout(function(){
logger.debug("Inside Call back function - ");
//function call for ticket creation
incidentRequest(sitn_id,confUtil.config.mule_url);
}, 10);

You really should show more of the code that makes the request, though it seems as if you are doing some ajax inside your 'incidentRequest', so I will presume that (if that isn't what you are doing, then please, show your code....) - and since you tags say javascript and jquery - well, here goes...
To stop the 'double send' in an AJAX call, it is simple:
function incidentRequest(sitn_id,confUtil.config.mule_url){
// stop the double by clearing the cache
$.ajaxSetup({cache: false});
// continue on with the AJAX call
// presuming the url you want is confUtil.config.mule_url
// and the data you want to send is sitn_id
$.post(confUtil.config.mule_url, 'sitn_id=' + sitn_id, function (data) {
// do cool stuff
});
}
Hopefully that will help you get moving. If not, then we will need more code of what is going on around all this.

retrieve value from mysql database with php/javascript in refreshing window

i have script that works as follows:
there is main page with 'start' button that initializes javascript function which loads a php page into a div frame, then via setTimeout it calls a 'refresh' function thats supposed to work indefinitelly and refresh the page inside frame
the refreesh timer is in database and is forwarded to java like this:
var min_refresh_time = ;
$min_refresh_time_sec is taken from database earlier in the code
what i wanted to modify is so the refresh min_refresh_time would be taken each time a refresh function is run, to my surprise this worked (or at least i thought so):
var min_refresh_time = ;
(custom sql functions are defined in separate php file included in main.php which is my main page)
unfortunatelly it seems that it 'worked' only due to some strange caching on java part and my pseudo-php code to take value from database is just a hoax - it looks like it is run only initially and then stores output somehow
simplified code of what is done and what i want to do:
function refresh_code(){
refresh_time = <?php Print(sql_result(sql_execute("SELECT value FROM settings WHERE setting='min_refresh_time'", $connection), 0, 0)); ?>;
refresh_time = 5;
alert(refresh_time);
$.post("index.php",{refresh_time:refresh_time_post, account_group: "1"},
function(data)
{
$.ajaxSetup ({
cache: false,
});
$("#frame_1").html(data);
});
setTimeout(function(){refresh_code()}, refresh_time);}
lets say min_refresh_time is 1 in database, i run it, it alerts 1 then 5 each time it self-refreshes, now if i go to database and change 1 to 3 i would want it to alert 3 then 5 obvious, it still does 1 then 5 tho...
i need a way to execute a dummy php file that only takes value from database, then sends it via post back to java and it gets intercepted there, any simple way to do that?
or do i need to use entirely different method for retrieving database value without js...
thx in advance
update:
i actually came back to it and analyzed potential solutions with fresh mind
first of all, i dont think my initial code had chance to work, java cant execute serverside code by itself, i took some of my aax code from other script and reworked it to launch php file that grabs the value from database, then i intercept output data and put into variable
looks like that:
$.ajax({
method: "POST",
url: "retrieve_refresh.php",
data: { retrieve_data: "max"},
cache: false,
timeout: 5000,
async: false,
cache: false,
error: function(){
return true;
},
success: function(msg){
if (parseFloat(msg)){
return false;
}
else {
return true;
}
}
}).done(function(php_output2) {
max_refresh_time = php_output2;
});
retrieve_refresh.php returns only the variable i want but the solution is unelegant to say the least, i havent searched yet but could use a way of sending variables as post back to ajax...

How to refresh a location w. javascript when the location has a target?

This is similar to, but not the same as How can I refresh a page with jQuery?:
I bring up a modal form that collects some stuff from the user and passes it off to the server via a $.ajax() call. The server sends back a path that should become the new window.location of the browser. So the ajax call wants to be something like:
$.ajax({
// stuff
success: function (destination) {
// other stuff
window.location = destination;
}),
// still more stuff
});
This works fine as long as destination is a pure path, like /some_path and if the browser is not currently on that page. However, if the path is the page that I'm currently on and also includes a target -- /some_path#some_target, I lose: the browser simply repositions the page at the specified target, but does not hit the server for a fresh view of the page, which I need (since the server has done some stuff during the ajax call).
So, maybe I just add a location.reload() after the window.location call? That would work when the code is running on the page to which it's being returned, I think. But if I'm on another page, I get hit by a race condition, where the reload is called before the browser has finished making the window.location change, and I get the old page reloaded, not the new destination.
Blurgh. Is there any way around this?

One approach would be to check if window.location.pathname (which is the path without # or ?) is the same as destination within your success callback:
success: function (destination) {
// other stuff
if (destination === window.location.pathname) {
window.location.reload(); // reload if we are on the same page
} else {
window.location = destination; // otherwise, navigate to "other" page
}
}),

window.location.reload() reloads the current page with POST data, while window.location.href=window.location.href does not include the POST data.

jquery ajax async false is not working

I have a python script that's doing around 8 or 9 specific steps. These steps are being logged in a file. For web GUI to display status change, or error messages, I am using the script belowjquery PeriodicalUpdater plugin.
I need the program to run simultaneously so that as the value in the file changes,it gets polled and displayed.
Please find my jquery code below.
Note the url "/primary_call/" takes around 2 and half minutes to execute. Problem is async :false is not working. The browser waits for 2.5 minutes, and then gets into the next level.
I tried in Firefox and Chrome and it gives the same result.
When I call the URL of another browser tab, it works perfectly, but I am unable to run both script components simultaneously, when I try calling from the same page.
What should I do so that the browser initiates "/primary_call/", which runs a Python script in the background, at the same time moving ahead to the portion called PeriodicUpdate.
$(document).ready(function()
$.ajax({
type: 'GET', // Or any other HTTP Verb (Method)
url: '/primary_call/',
async: false,
success: function(r){
return false;
},
error: function(e){
}
});
$.PeriodicalUpdater({
url : '/static/12.txt',
method: 'post',
maxTimeout: 6000,
},
function(data){
var myHtml = data + ' <br />';
$('#results').append(myHtml);
});
})

Setting async:false means you are making the process synchronous, so the browser will hang on it until it is finished -- it can't move on to your other method. Removing that option will make the call asynchronous (which it is by default, as it should be) at which point the browser will initialize each ajax call in a separate thread.
In short, remove async:false.