Is it possible to run a php script after every 100ms ? This script will check a database for changes and then the changes will be reflected into some other database. I am already doing it using Triggers. But I want to know if there is any other way to do it without using Cron and Triggers. I will be using Linux for this purpose.
Thanks
Running something every 100ms almost means that it runs all the time , might as well create a daemon that continuously loops and executes
or use triggers. Essentially on every database change it will copy to another table/db.
http://codespatter.com/2008/05/06/how-to-use-triggers-to-track-changes-in-mysql/
It is not possible to do this with cron (it has a max frequency of one minute) and this is a really bad idea. You will be running a whole new php interpreter ten times per second, not to mention doing database connection too.
Far better perhaps would be to run one program that re-uses it's connection and checks every second or so.
Sounds a little like you are trying to make your own database replication or sync between two databases.
You could write a daemon to do it, essentially a script which continually runs in memory somewhere to then run whatever code you want to.
So that daemon would then do the database processing for you, and you wouldn't have to call a script over and over again.
Use your favorite programming language and set up a permanent loop to run it every 100ms, then put the script into inittab with 'respawn' (man inittab for complete syntax). Finally, init q to reload init.
It's best if you write a little daemon for that. Use the pcntl functions to do so. In your case you might get away with:
<?php
while (1) {
usleep(100000);
if (pcntl_fork() == 0) {
include("/lib/100ms-script.php");
exit;
}
// else pcntl_wait(); eventually
}
I'm assuming that this is in reference to some type of web page to be created. If so, this sounds like this is a job for Ajax, not PHP. As you may already know PHP processing is done on the server side. Once processing is complete the page is served up to the client.
With Ajax/JavaScript processing can continue via the browser. You can setup a timer that can then be used to communicate with the server. Depending on the output of the response the page may be updated to reflect the necessary changes.
Related
I am developing an web application using php and mysql along with AJAX. In one of my script there is a provision to fetch data from mysql table. But what if I want to cancel the execution of the php script which I am calling to get the data, in the middle of the execution? Let me clear it more. Like if it takes say 30 minutes to complete an AJAX call due to the heavy loop and I want to exit from that call before completion by clicking some button. How can I achieve that goal. Otherwise, my script is running well except that it hangs if I don't want to wait for the final AJAX response text and try to switch to other page of the web application.
You can create script like this:
$someStorage->set($sessionId . '_someFuncStop', true);
Call it through AJAX, when button STOP pressed.
In your script with loop check that var from storage
while(1) {
if ($someStorage->get($sessionId . '_someFuncStop') === true ) break;
}
To my best knowledge, PHP doesn't support some sort of event listeners that can interrupt running script by an external cause.
There are 2 paths you might want to consider (if you don't want to write shell scripts on the server that would terminate system processes that execute the script):
ignore_user_abort function, thoug it is not 100% reliable
http://php.net/manual/en/function.ignore-user-abort.php
Inside the loop you wish to terminate, create a database call (or read from a file), where you can set some kind of flag and if that flag is set, run a break/return/die command inside the script. The button you mentioned can then write to database/file and set the interrupt flag.
(In general this is not really useful for script interruptions, since most scripts run in tens of milliseconds and the flag would not be set fast enough to terminate the script, in tens of minutes however, this is a viable solution.)
I'm pretty new to PHP. This is my first time actually, so I apologize in advance if the question sounds dumb.
I have a php script which fetches data from an external API and updates my database regularly. I know that the best way to do this is to use a cron job. However, I am using an infinite loop which sleeps for a particular time between each update.
Now, I need to allow the user (admin) to start / stop the script and also allow them to change the time interval between each update. The admin does this through a UI. What is the best way to do this? How do I execute the script in the background when the user clicks start and how do I stop the script?
Thanks.
I think the ideal solution would be the following:
Have the background job run as a cronjob every minute (instead of a loop which can cause memory leaks). PHP was not designed to be a daemon.
Set a DB flag in the cronjob for on/off, everytime it runs it checks if its on or off, if off it exists if on it continue.
In the UI you turn that flag on or off depending on what the admin needs.
I think that is the best way to go (and easiest).
You might want to take a look at Threading in PHP -> http://www.php.net/manual/en/class.thread.php
An other option is to either set a SESSION (which is a little tricky, since you won't catch it in the same call) or you generate a file wich tells the script to stop/exit/fail/what ever if that file exists.
How can I make a scheduler in PHP without writing a cron script? Is there any standard solution?
Feature [For example]: sent remainder to all subscriber 24hrs b4 the subscription expires.
The standard solution is to use cron on Unix-like operating systems and Scheduled Tasks on Windows.
If you don't want to use cron, I suppose you could try to rig something up using at. But it is difficult to imagine a situation where cron is a problem but at is A-OK.
The solution I see is a loop (for or while) and a sleep(3600*24);
Execute it through a sending ajax call every set interval of yours through javascript
Please read my final opinion at the bottom before rushing to implement.
Cron really is the best way to schedule things. It's simple, effective and widely available.
Having said that, if cron is not available or you absolutely don't want to use it, two general approaches for a non-cron, Apache/PHP pseudo cron running on a traditional web server, is as follows.
Check using a loadable resource
Embed an image/script/stylesheet/other somewhere on each web page. Images are probably the best supported by browsers (if javascript is turned off there's no guarantee that the browser will even load .js source files). This page will send headers and empty data back to the browser (a 1x1 clear .gif is fine - look at fpassthru)
from the php manual notes
<?php
header("Content-Length: 0");
header("Connection: close");
flush();
// browser should be disconnected at this point
// and you can do your "cron" work here
?>
Check on each page load
For each task you want to automate, you would create some sort of callable API - static OOP, function calls - whatever. On each request you check to see if there is any work to do for a given task. This is similar to the above except you don't use a separate URL for the script. This could mean that the page takes a long time to load while the work is being performed.
This would involve a select query to your database on either a task table that records the last time a task has run, or simply directly on the data in question, in your example, perhaps on a subscription table.
Final opinion
You really shouldn't reinvent the wheel on this if possible. Cron is very easy to set up.
However, even if you decide that, in your opinion, cron is not easy to set up, consider this: for each and every page load on your site, you will be incurring the overhead of checking to see what needs to be done. True cron, on the other hand, will execute command line PHP on the schedule you set up (hourly, etc) which means your server is running the task checking code much less frequently.
Biggest potential problem without true cron
You run the risk of not having enough traffic to your site to actually get updates happening frequently enough.
Create a table of cronjob. In which keep the dates of cron job. Keep a condition, if today date is equal to the date in the creonjob table. then call for a method to execute. This works fine like CRON job.
Say I want a php script the run the function itstime() every hour. Other than setting up a cron job on the server how can I do this?
Or is this not possible because php scripts need to be opened to be ran?
Thanks.
EDIT: I want to write some information to a log file and depending on some variables send it in an email.
Well, I definitely recommend the cron job for the purpose. But theoretically, you could have a PHP script run itstime(), sleep for an hour, and loop. This is pretty crazy, though.
The script would look like:
<?php
include('whatever.php');
while(true) {
itstime();
sleep(3600);
}
?>
One would probably run it with nohup php mycrazyscript.php & to detach it from your terminal and make it keep running, and using pkill -f mycrazyscript to terminate it.
The reason this is crazy is that now you've got a sleeping PHP process hanging around doing nothing for 59 minutes out of every hour, and you have to make sure it's both running and running at the right time, both of which cron would take care of for you.
Only appending to chaos' answer, so give him credit.
mrlanrat - see this
If you don't have access to cron, but do have access to a moderately busy webserver, you can use it to trigger your function every hour. This is how WordPress gets around needing cron. Here's how you might do it:
<?php
$lastrun = get_last_run_time(); // get value from database or filesystem
if( time()-$lastrun > 60*60 ) {
itstime();
set_last_run_time(time()); // write value back to database or filesystem
}
// The rest of your page
?>
Of course, there's a pretty serious race condition in this code as is. Solving that is left as an exercise to the reader.
https://www.setcronjob.com/ and various other sites, provide a web based solution for this. You can set it up to call a php script with your code in it every hour or whatever you want
<?php
itstime();
?>
Basically I need to get around max execution time.
I need to scrape pages for info at varying intervals, which means calling the bot at those intervals, to load a link form the database and scrap the page the link points to.
The problem is, loading the bot. If I load it with javascript (like an Ajax call) the browser will throw up an error saying that the page is taking too long to respond yadda yadda yadda, plus I will have to keep the page open.
If I do it from within PHP I could probably extend the execution time to however long is needed but then if it does throw an error I don't have the access to kill the process, and nothing is displayed in the browser until the PHP execute is completed right?
I was wondering if anyone had any tricks to get around this? The scraper executing by itself at various intervals without me needing to watch it the whole time.
Cheers :)
Use set_time_limit() as such:
set_time_limit(0);
// Do Time Consuming Operations Here
"nothing is displayed in the browser until the PHP execute is completed"
You can use flush() to work around this:
flush()
(PHP 4, PHP 5)
Flushes the output buffers of PHP and whatever backend PHP is using (CGI, a web server, etc). This effectively tries to push all the output so far to the user's browser.
take a look at how Sphider (PHP Search Engine) does this.
Basically you will just process some part of the sites you need, do your thing, and go on to the next request if there's a continue=true parameter set.
run via CRON and split spider into chunks, so it will only do few chunks at once. call from CRON with different parameteres to process only few chunks.