SimpleXML lock file

[keben]

Hey dudes,

 

I have an application that must access a jnlp file (xml, java web start), and change it with the choices of a user with simpleXML. The problem is that there's a probability that this happens with simultaneously users. How do i lock the file for the user that gets there in first place?

 

Cheers n Beers

[mikr]

I grabbed this from the php documentation:

<?php

$fp = fopen("/tmp/lock.txt", "w+");

if (flock($fp, LOCK_EX)) { // do an exclusive lock
    fwrite($fp, "Write something here\n");
    flock($fp, LOCK_UN); // release the lock
} else {
    echo "Couldn't lock the file !";
}

fclose($fp);

?>

[keben]

Hey,

 

I know the existence of flock, the problem is that $f1 = fopen() and $f2 = simplexml_load_file() are different things, so if i open the file  with $f1 i can't change it with $f2.

[mikr]

Since simplexml_load_file() is read only, that shouldn't be a problem, should it? However, just for fun, supposing you still want to lock it, you don't have to lock the file itself. Let's say your file is whatever.xml. Then, if you want to be sure you are the only one reading whatever.xml (but you can't use fopen/flock), you can use fopen/flock on whatever.xml.lock. Essentially, you are creating your own lock system using filenames.

So, when you are about to read the xml file, you first attempt to fopen/flock the xml file with a ".lock" extension. If you can do that, then you go ahead. If not, then someone else has a lock.

There are two downsides. If a process dies before the lock file is deleted, you are stuck having to ftp in (or whatever) and delete it by hand. Also, you have to police your own locking and unlocking.

[keben]

hey,

 

Thanks for the suggestion, i think i have an idea what to do know

 

Gracias pal 

[keben]

Hey,

 

I follow your suggestion, i created a dummy.lock file to open and lock and then manage the other file, well it didn't work. I tried with two users acessing at the same time, and both did the code in the supposed locked part (just some echo's).

 

Ciao.