php: exclusive lock on file never obtained

Question

On my php script, after parse a string, i need to write some data into a file (after create it if doesn't exist). Before write file, i need exclusive lock for avoid problems. This is my code:

foreach ($elements[0] as $current) {
    $file_handler = fopen($my_folder . "/" . $current . ".txt", "a");
    $locked = flock($file_handler, "LOCK_EX");
    while (!$locked) {
        usleep(500000);
        $locked = flock($file_handler, "LOCK_EX");
    }
    //got lock
    fwrite($file_handler, $mystring . "\n");
    //release lock
    flock($file_handler, LOCK_UN);
    fclose($file_handler);
}
return;

Now, something seems not work. fopen create file, but my code seems go in loop inside while (file is created, but nothing was write inside). What's wrong?

Answer 1

You are passing the argument for locking as a string instead of a constant.

Try:

$locked = flock($file_handler, LOCK_EX);

Notice the missing double quotes around LOCK_EX