I am simulating push notifications using PHP the following way:
A jQuery ajax call calls a script on the server.
The script is being delayed using a for loop and a sleep after each iteration.
If something happens - the loop is being breaked and the information returned to the jQuery.
If the script runs for more than one minute - the script returns an empty value.
When the jQuery receives an answer from the server it parses the information and starts the same procedure again.
That's a procedure, used by facebook and it works like a charm on their website. On my server I have the following problem:
For example if the script is being delayed for 60 seconds and I click on another link on my website on the 30-th second we still have 30 seconds left to generate the output. So my webserver is waiting those 30 seconds and my click request is being processed after those seconds, making my website almost impossible to use. I have doublechecked facebook and I found that, when you click on a link the page is never refreshed and the requests keep flowing on the same page. The adressbar however changes. What is the way to achieve the same thing on my website? Is there a way to force my server to process more then one PHP request at a time or we have to do this using javascript only. What am I missing?
P.S as far as I know there is no way to change the adressbar using javascript.
Actually there is in HTML 5. It's called History API.
You could find a quick demo with the source code on GitHub here:
http://html5demos.com/history
The complete chapter about it in Dive Into HTML5:
http://diveintohtml5.info/history.html
Related
I'm trying to force to reload a (second) page if a criteria is met in php
But if the criteria is met, i want the page to force reload everywhere, even if 10 people have it open at once for example.
for simplicty lets say the code is like this:
in /filelocation/script.php:
if {$data == "ok"}{
reload/refresh "reload.php" if it's open somewhere;
}
I came across a software that basicly does this, and i want to understand how this is done.
(it works cross device somehow, so i asume its done through php somehow)
Well, in your PHP code, you cannot simply reload/refresh something for all the users connected. This is simply because the PHP code is only executed when your browser requests a page on the server so it's only executed to build the HTML response and then it stops executing. Once the browser has the HTML response it will render the page and then it waits for an action from the user to do something else (such as clicking on a link or posting a form).
I imagine that you would like that when a specific user does something, like posting a comment or buying a product, you would like all the other visitors to be notified that a new comment has been posted or that the number of products available has been reduced.
To do that, you need to implement some JavaScript which is executed in the browser of each visitor. The idea is to keep a connection with the server with the help of web sockets. This way, you can inform the browser that something has changed.
You could google to find some examples of PHP apps using web sockets. The first example I found:
https://www.twilio.com/blog/create-php-websocket-server-build-real-time-even-driven-application
Another solution could be to have some JavaScript doing some pooling, meaning that every N seconds, it executes an Ajax request to the server to ask if something has changed. This can be done with the help of setTimeout(yourFunction, 10000) to call a JavaScript function every 10 seconds. This function will do the Ajax request and then update the part of your page that needs to change. Just be carefull that if you get a lot of users on your site then you'll produce quite a lot of load on your server. So this wouldn't be a good solution, but it could be an alternative to the web sockets.
I would like to find a way to have my user not having to wait for the output of a php script and being redirected to a page while the script is running on the server.
Basically the user submits a form which takes quite long to process and I would like to redirect the user to a page notifying him that the form is being processed and that its output will be later available (I thought about opening a tab when the output is ready).
Basically I would like something like this, which I tried without success, the
if ($form_valid) {
process_form(); // this would need not to be running on the current page so that the user don't have to wait for it to be ready (timeout problems)
header('Location: http://example.com/form_submitted_output_coming_soon.html');
}
I hope that it is not too vague.
Thank you in advance for any help / advice on how I could do that.
It really depends on the time the script takes to execute if it's seconds, under 10 I would do an ajax request and have a modal progress message
If they take extended amounts of time my approach would be to create or use an existing task scheduler/ report generator
a single system scheduled task entry calling a central management script ( probably not optimal )
You mark a task/report for execution
Concurrency. Count, limit the number currently executing ( so you don't over load the server)
users pool via ajax for their tasks / reports or push to the clients with web sockets
Example on how to fork php to background
Update
I think you would get better performance out of a bot continuously check a database or file for work to do and submitting results back to the database. Alerting users via ajax, web sockets and or email when the work that they need is done / updated.
Here is a good introduction on how to build a web crawler in php
The best approach for solving this kind of problem is to use AJAX to make the request to the server in the background and then update the user once it has finished processing.
You may submit the form with an asynchronous request (ajax) and handle the page forward also with javascript. This way your form is handled asynchronously - you may even wait for the response to tell the user once you have an answer. This asynchronous request will not block the UI.
Just for completeness if you really really want to use php only for this:
Run PHP Task Asynchronously
Here is the scenario:
I have a page that is logging data to MYSQL. I have another page that reads that data and allows it to be viewed. When a new piece of data is logged I would like to have the first script check and see if the viewing page is open in the browser, and if so append the newest data to the end of the view. Also - could anyone point to some info giving an overview of how PHP and the browser interact? I think I have the concept of the DOM down for javascript...but as far as PHP it just appears that once the page is sent, that's it...
You're correct in that once the PHP is sent, that's it.
There is no way to send data to a PHP page once the page is loaded. There is another slightly nastier method, but the easiest way of doing this is going to be polling the page via Ajax.
So, have a script that every 20 seconds, sends a message to another PHP script that contains the timestamp of the last MySQL log you received, then get the script to return all the data that has been set by that time.
I'm unsure how new you are to JavaScript, but the easiest way of doing that is probably using JQuery's $.ajax and encoding the new MySQL records as JSON.
No this isn't possible as you describe. The viewing page will have to poll the server for changes, either by periodically reloading itself, or by javascript / AJAX.
You are right that once the page is sent by PHP it can have no further influence. In fact the PHP execution thread on the server is killed as soon as output is complete, so the thing that generated the page no longer even exists.
To expand on Dolondro's suggestion, rather than periodically polling the server for updates, you could use Server-Sent-Events (newly supported in modern browsers).
With these, you basically just send 1 ajax request to the server, and the connection is held open. Then, the server can send updates whenever it wants. When the browser receives an event, it can add the data to the screen. Even still, the connection is held open, and the server can send additional events/updates as they occur.
W3C page:
http://dev.w3.org/html5/eventsource/
Wikipedia:
http://en.wikipedia.org/wiki/Server-sent_events
More Info:
https://www.google.com/search?ix=hcb&sourceid=chrome&ie=UTF-8&q=server+sent+events
I've looked all over for any answer on this and haven't been able to find one, hopefully someone can point me in the right direction, I think I'm close
I have two hosts let's call them host1.mydomain.com and host2.mydomain.com (to get around the 2 concurrent connections per host/per browser issue), so they both point to the same content one is just an alias of the other
User goes to host1.mydomain.com, enters some information to register, clicks Go, which loads an iframe on the same page pointing to a page on host2.mydomain.com which calls a php script via exec("curl") sending the request to the background to start a website scraper, the process ID is then stored in the database for the user. After the iframe has successfully loaded (only takes 1 second since it's creating a background process) I have an AJAX request set on an interval to check the status periodically of the cURL process (by it's process ID in the database) so that I can display the current step of the scraper (there are 6 steps in total). All good so far.
The problem is that the AJAX requests are timing out after step 4 of the scraper (browser default timeout is 115/120 seconds) even though it shouldn't be because I'm working with two different hosts...meaning to say that it's almost as if I'm clogging both connections on host1.mydomain.com when I'm not because I initiated the scraper from host2
The iframe loads this URL: http://host2.mydomain.com/page.php
The contents of the PHP script calls:
exec("curl -o /dev/null 'http://host2.mydomain.com/page.php?method=process' > /dev/null & echo $!", $op);
Then my ajax request is polling http://host1.mydomain.com/status.php?pid=x which looks up in the database to check the status by the process ID
and once the scraper gets to step 4, my ajax requests are timing out
I think I confused myself explaining this, but hopefully someone can help me
Turns out I was successfully getting around the 2 connections per server/browser limitation...however in doing some research I found the reason why my ajax request was hanging is because I was trying to access and write to the session data from both of the requests. Digging a little deeper I found a session_write_close() which closes the session for reading/writing, I basically have to call this after each page request of the scraper and then reinitialize the session, this allows my ajax requests to go through and stops the blocking of the request.
Hopefully someone else finds this useful if you stumble across the same issue
Cheers!
Jeff
Instead of waiting for the request to finish, you should spawn new process which runs in the background on server. And use javascript to "check back" each few seconds to see when the execution has finished. Then all you have to do is pick up the result and display it.
Additionally you might want to make sure that only one php process is spawned.
I have a request to provide the following solution:
Two web pages with 1 form on them. This form is submitted and inserted into a database. Another web page is used to display the results of the form inputs in a tag cloud solution. My question is what exact workflow would people use for this? My thoughts were like so:
1 MySQL database, 1 html page running AJAX and jQuery for the tag cloud/polling. 1 PHP processing script which grabs new data from the database and serves it out to the html page. Now, what is the effect of this being ran for say 24 hours, constantly updating via AJAX ie, every 10 seconds or should i use a different method. The results from the form need to be saved for offline viewing after the 24 hour period, so i cant just stream the form results straight to the page.
All advice welcome using any technologies...
Should add, there's a possibility that it may be on a LAN with no internet access, possibly thinking of a local XAMPP installation...
given that there is 3 clients, and they poll every 10 sec, that means
approx 25k requests per day to keep the page updated. which is hardly any load for a xampp install, especially on a local network.
i would suggest testing the polling and see if it still works after 24hours.
are there any limitations in the browser that stop the script from working after x amount of time. (i have never tried that long before sorry)
an alternative approach is,
does it need to poll continuously, or can you just have a refresh button