I was wondering if is is possible to send output from application ran by php to client.
For example i have application that outputs:
Hello world
And after 10 seconds it outputs
10 seconds passed
I'd like to know if it is possible to send "Hello word" and "10 seconds passed" to client without waiting until whole program finishes its job. Client would receive "Hello world" first and after 10 seconds second output.
Thank you.
Your title says "Asynchronous external aplication execution". By this, you would mean something that will execute a program from your PHP script, yet continue on its own process and not hang PHP page load. You may want passthru() specifically setting the command to output to a local file rather than your script (personally not tested, though the PHP manual says you can), or pcntl_fork() to split off your script into a separate process which will handle the program execution on the side. However, double-sending to a browser after it had already disconnected from your server and expecting it to display your uninvited message is impossible unless you install a trojan on the client which will auto-accept your second, new tcp forced connection.
But, if you want a progress message for your page load, simply echo "still loading..." anywhere along a number of for or while loops. File download progress bars on the other hand cannot be dealt with in PHP. Echoing "still loading..." in the middle of the download will corrupt the file. At the moment, I'm not aware of any facility to do this using any PHP, Javascript, or VB method, except in the browsers own API (if documented) if the client allows it by installing a plugin you authored. But why, when browsers already have built-in progress bars?
I think you should do this with javascript. It's totally unnecessary to use cpu-cycles on the server until all of your requirements are that show time passed.
Usually, a client pulls content from the server. If you want to push from the server to the client, you need to look into push technologies like Comet. There is not too much available for PHP though. Periodically pushing with the PHP script terminating inbetween requires a Message Queue.
I don't understand your application, but for batch processing this comes to mind:
php hello-world.php | php client.php
To scale it, use Hadoop.
Related
I'm making a app for my website for visitors to look at the camera.
I own a PT( pan-tilt) camera which can be operated by using url's.
I want my camera to move randomly at prefixed times ( like every 5 seconds a different position) and in the background, so i will move without any operator but i can't seem to figure out how to make it movable automatically.
The manufacturer works with CGI commands like:
myip:myport/decoder_control.cgi?command=39&user=user&pwd=password
(this code makes it go to preset 1).
How can i make the camera move with this command using serverside php, making it move after 5 seconds?
Running the CGI script from PHP.
You can perform an HTTP request from PHP, that would load the URL corresponding to the command, causing the camera to change position. Some ways of achieving this:
Using the function http_get: PHP: http_get – Manual.
Using cURL.
Using file_get_contents for very basic requests: question on SO.
If you just need to perform a GET request, and the response is empty (e.g. you just need to check the +200 OK code) or contains some very simple data (e.g. a string), then file_get_contents is more than enough.
If you don't have any background on how HTTP requests work, Wikipedia could be a good introduction; especially if later on you have more complex CGI commands to send to your PT Cam.
Make the camera move every 5 sec.
This is a completely different matter. The problem here is run PHP code periodically and automatically.
You can schedule the PHP script to be executed, using a Cron job (Cron, crontab) and this questions explains you how. BUT Cron's minimal time resolution is one minute; also moving a camera every 5 seconds doesn't really sound like schedule a job, sounds more like it should be handled by a system service.
What you could do, is moving the camera from the PHP script users use to watch: store the last update time on a file/database, and if the elapsed time is >5s, run the CGI script.
This would keep your camera still unless someone is actually watching. Other problems might arise, for example what if many users are visiting the same page and your server serves the request simultaneously? You might get several consecutive commands sent to the camera. Moreover, while the users are watching, staying on your PHP page, you must again find a way of moving the camera every 5".
A possible solution.
Create a PHP script that, when loaded, runs the CGI command only if at least 5s have passed since the last call (by storing the time of the last call).
Create a client page for your users, that, via JavaScript, loads the PHP script every 5s. Look for JavaScript GET request, you will find enough information to fill a book.
Again, this would generate a lot of traffic on your webserver, just for those five seconds of panning. My suggestion is that the movement should be handled by some server side program, not script.
Why in Chrome, when I hit "STOP" button when PHP script is executing, it does not stop execution? Even closing TAB doesn't stop it. ignore_user_abort() is false. Any ideas on how to force PHP to stop? Got large script, that makes some big files and executes for like 10 minutes...
There is no way for a user to stop a PHP script. Since PHP is run on the server when a page is called, you cannot stop it unless you have a condition in your script that will quit to your liking.
As I mentioned in a comment, this answer to a previous question has a lot of info on this.
But one takeaway that may be your issue: PHP may not know it's disconnected until it tries to send data and is refused, see this bit in the docs:
the next time your script tries to output something PHP will detect that the connection has been aborted
So depending on your required output, you may be able to send some sort of "heartbeat" data to the browser that will trigger the abort if the user disconnects. If it doesn't seem to be sending, try doing some explicit buffer-clearing with flush(). If you (or your framework) are using output buffering, you may have to work around it.
If you can't do that (if you're generating an output file or some such), you'll likely have to rearrange things, since there's no way PHP can know the connection is closed. My suggestion is to use a queueing system to offload the generation of things to a separate script that you can then cancel/kill manually - here's a good overview of queueing systems, I personally use beanstalkd with PHP - it's simple, easy, works splendidly, and has some good PHP libraries (I've used pheanstalk and davidpersson's beanstalk). Any time you're generating large files like that, you should probably be using a queueing system anyway.
I'm trying to find a solution to my problem with sending data to client with PHP. The biggest issue is - what I'm trying to do is to keep sending data inside a single connection with PHP script. I'm sure there are other ways but currently I don't know how to solve this.
What I'm trying to do is: A client connects to a web server and keeps the connection opened, so the TCP connection is "established". He will keep making for example GET requests every X seconds to keep this connection alive.
Inside of this connection on certain event I want to send the client some data without him making the request! So it means the event is triggered on the server side, not on the client side.
There is no possibility of using any JavaScript or any client-side technique as my client is Arduino module. I can keep the connection opened but I need to pass data to the client by using HTTP.
I have a database set up on the server and PHP will send data to the client when something changes inside the database.
I was trying to play with php flush() running in loop in the PHP script; but that doesn't do it the way I want.
So any advices appreciated.
Thank you.
edit: would be perfect it the solution would also work on Windows machine!
edit2: There will be multiple clients, not just one (eg hundreds)
As long as you don’t have lots of clients, Server-side Events sounds like it could work for you.
http://dsheiko.com/weblog/html5-and-server-sent-events
Just read that you will have hundreds of clients, in that case you probably won't want to use PHP but use node.js instead.
How about CRON jobs?
http://en.wikipedia.org/wiki/Cron
http://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/
I think that might be the solution for your project. If i undrestand CRON's correctly, what thy do is execute a given script at given intervals. So that is basicly what u want, scripts to execute for every X seconds. And inside your script u have your function working with the database.
I think what you are looking for is IPC - Inter Process Communication. In your case I would suggest a message queue (or multiple of those)
(On the client)
Open connection to foo.php
When receiving a new line, process it.
If connection times out, re-open it
(On the server - foo.php)
Open a Message Queue (You will have to register a message queue for each user!)
Register it so that your bar.php knows about it.
Start a blocking receive.
When a message is received, send whatever you want to send, FLUSH OUTPUT BUFFERS, go back to 2.
If anything times out, back to 2.
(On the server - bar.php)
When the database changes, send message to all active queues
There are a few problems with this approach:
The server side only really works on Linux / Unix (that includes Macs)
There is a limited number of message queues
You may have to do some housekeeping, removing old queues, etc.
The benefits:
This is application independent. Message queues are an operating system feature, thus your bar.php could really be say a java application.
Ok, so I think I found the way I want it to work. The problem why flush() wasn't working is that I didn't reach the flush buffer limit before flushing. Also I'm using Nginx server and I disabled gzip (just in case).
My test code which absolutely works looks like this:
<?
ob_implicit_flush(1);
for($i=0; $i<10; $i++){
echo $i;
//this is for the buffer achieve the minimum size in order to flush data
echo str_repeat(' ',1024*64);
sleep(1);
}
?>
Found my answer here: PHP Flush that works... even in Nginx
I will test it with my Arduinos if it can accept such output. Thanks all for your help.
I created a script that gets data from some web services and our database, formats a report, then zips it and makes it available for download. When I first started I made it a command line script to see the output as it came out and to get around the script timeout limit you get when viewing in a browser. But because I don't want my user to have to use it from the command line or have to run php on their computer, I want to make this run from our webserver instead.
Because this script could take minutes to run, I need a way to let it process in the background and then start the download once the file has been created successfully. What's the best way to let this script run without triggering the timeout? I've attempted this before (using the backticks to run the script separately and such) but gave up, so I'm asking here. Ideally, the user would click the submit button on the form to start the request, then be returned to the page instead of making them stare at a blank browser window. When the zip file they exists (meaning the process has finished), it should notify them (via AJAX? reloaded page? I don't know yet).
This is on windows server 2007.
You should run it in a different process. Make a daemon that runs continuously, hits a database and looks for a flag, like "ShouldProcessData". Then when you hit that website switch the flag to true. Your daemon process will see the flag on it's next iteration and begin the processing. Stick the results in to the database. Use the database as the communication mechanism between the website and the long running process.
In PHP you have to tell what time-out you want for your process
See PHP manual set_time_limit()
You may have another problem: the time-out of the browser itself (could be around 1~2 minutes). While that time-out should be changeable within the browser (for each browser), you can usually prevent the time-out user side to be triggered by sending some data to the browser every 20 seconds for instance (like the header for download, you can then send other headers, like encoding etc...).
Gearman is very handy for it (create a background task, let javascript poll for progress). It does of course require having gearman installed & workers created. See: http://www.php.net/gearman
Why don't you make an ajax call from the page where you want to offer the download and then just wait for the ajax call to return and also set_time_limit(0) on the other page.
I've written in PHP a script that takes a long time to execute [Image processing for thousands of pictures]. It's a meter of hours - maybe 5.
After 15 minutes of processing, I get the error:
ERROR
The requested URL could not be retrieved
The following error was encountered while trying to retrieve the URL: The URL which I clicked
Read Timeout
The system returned: [No Error]
A Timeout occurred while waiting to read data from the network. The network or server may be down or congested. Please retry your request.
Your cache administrator is webmaster.
What I need is to enable that script to run for much longer.
Now, here are all the technical info:
I'm writing in PHP and using the Zend Framework. I'm using Firefox. The long script that is processed is done after clicking a link. Obviously, since the script is not over I see the web page on which the link was and the web browser writes "waiting for ...".
After 15 minutes the error occurs.
I tried to make changes to Firefox threw about:config but without any success. I don't know, but the changes might be needed somewhere else.
So, any ideas?
Thanks ahead.
set_time_limit(0) will only affect the server-side running of the script. The error you're receiving is purely browser-side. You have to send SOMETHING to keep the browser from deciding the connection's dead - even a single character of output (followed by a flush() to make sure it actually get sent out over the wire) will do. Maybe once every image that's processed, or on a fixed time interval (if last char sent more than 5 minutes ago, output another one).
If you don't want any intermediate output, you could do ignore_user_abort(TRUE), which will allow the script to keep running even if the connection gets shut down from the client side.
If the process runs for hours then you should probably look into batch processing. So you just store a request for image processing (in a file, database or whatever works for you) instead of starting the image processing. This request is then picked up by a scheduled (cron) process running on the server, which will do the actual processing (this can be a PHP script, which calls set_time_limit(0)). And when processing is finished you could signal the user (by mail or any other way that works for you) that the processing is finished.
use set_time_limit
documentation here
http://nl.php.net/manual/en/function.set-time-limit.php
If you can split your work in batches, after processing X images display the page with some javascript (or META redirects) on it to open the link http://server/controller/action/nextbatch/next_batch_id.
Rinse and repeat.
batching the entire process also has the added benefit that once something goes wrong, you don't have to start out the entire thing anew.
If you're running on a server of your own and can get out of safe_mode, then you could also fork background processes to do the actual heavy lifting, independent of your browser view of things. If you're in a multicore or multiprocessor environment, you can even schedule more than one running process at any time.
We've done something like that for large computation scripts; synchronization of the processes happened over a shared database---but luckily enough, they processes were so independent that the only thing we needed to see was their completion or termination.