Possible methods to send the output of a PHP-invoked .exe program (that runs as a separate process, not in PHP) back to the iPhone client

Question

My iPhone client app uploads a data to the server, which runs on PHP. There is a code to invoke a .exe program on the server side on PHP. The .exe program will take the uploaded data and run on a process on its own. That means the PHP execution will end without waiting for the .exe program to finish. After the .exe program finished processing the uploaded data and have an output, I want this output to be sent back to the iPhone.

Normally, if we call the .exe program to be run inside the php without making it a seperate process, we have to wait for the program to finish and we can send the output back to the iPhone client.

By running the .exe program as a seperate process, it is impossible to send the data back via PHP that invokes the .exe program. The question is, if we have the .exe program running on a seperate process rather than on the PHP script, what are the possible methods to send the output back to the iPhone client?

Answer 1

I would say this is a perfect case for an AJAX snippet frequently polling data from, say, a text file the .exe writes its status in.

The upload script you call could return a unique identifier of some sort to the uploading client. Using that identifier, the client would poll the exe's status (e.g. "does the output file xyz already exist?") until it gets positive feedback.

Answer 2

You're going to have a hard time reconnecting with the iPhone once you've severed the connection. It may be out of coverage, it may have changed IP address, ......

Your best bet is to have the iPhone reconnect back to the server and poll for it's information.

Answer 3

That's a need problem you've outlined. Let me explain a couple of ideas.

First of all, if you terminate the initial upload request, the only resonable way to check for it being done is to poll every few seconds from the iPhone. Send a request to "get-update.php" every 5 seconds to see if you have data.

By using $_SESSION, you should be able to store a token that will identify the data when it has finished processing.

Regarding the actually process, you may be able to accomplish that in a number of ways. One is to do a fairly standard double-fork, detaching the child process from the parent, so it will continue after the parent exits.

Another (recommended) would be to author a backend server process that would watch your database for requests, fetch them, process them, and update the database. So when the inital upload script actually uploads the data, have PHP put it in the database, store the record ID in $_SESSION, and return to the user.

The back end process will notice that there is a record to process, read the data, call the executable, and update the database with the result.

The get-update.php script will read $_SESSION for the record id, and check the database if the data has been processed (or what the status is).

If you do not have the ability to run a background process, and you are constrained to using PHP, you could do the double-fork magic, and fork of another PHP process to do the database read / exe / database update.

Feel free to comment with questions.

You need (a) a good way to pass the data to the program, and (b) a good way to get the data back.

Answer 4

You could do this by using Apple's Push Notification service, but that's probably overkill, unless you think the data processing is going to take a long time, and/or you want to update the app icon when the processing is done, even if the app isn't running.

Do you expect the user to just be patiently waiting for the result, or are they going to fire off the data, and check back later? If it's only going to take a couple of seconds, you could just have the iPhone app poll for the result after waiting a little while (while displaying a progress indicator).