php flock behaviour when file is locked by one process

Question

Let\'s consider a sample php script which deletes a line by user input:

$DELETE_LINE = $_GET[\'line\'];
$out = array();
$data = @file(\"foo.txt\");
if($data)         


        

Answer 1

If you try to acquire an exclusive lock while another process has the file locked, your attempt will wait until the file is unlocked. This is the whole point of locking.

See the Linux documentation of flock(), which describes how it works in general across operating systems. PHP uses fcntl() under the hood so NFS shares are generally supported.

There's no timeout. If you want to implement a timeout yourself, you can do something like this:

$count = 0;
$timeout_secs = 10; //number of seconds of timeout
$got_lock = true;
while (!flock($fp, LOCK_EX | LOCK_NB, $wouldblock)) {
    if ($wouldblock && $count++ < $timeout_secs) {
        sleep(1);
    } else {
        $got_lock = false;
        break;
    }
}
if ($got_lock) {
    // Do stuff with file
}