It's important to understand that LOCK_EX will not prevent reading the file unless you also explicitly acquire a read lock (shared locked) with the PHP 'flock' function.
i.e. in concurrent scenarios file_get_contents may return empty if you don't wrap it like this:
<?php
$myfile=fopen('test.txt','rt');
flock($myfile,LOCK_SH);
$read=file_get_contents('test.txt');
fclose($myfile);
?>
If you have code that does a file_get_contents on a file, changes the string, then re-saves using file_put_contents, you better be sure to do this correctly or your file will randomly wipe itself out.
