PHP Simultaneous File Writes

Question

I have two different PHP files that both write to the same file. Each PHP script is called by a user action of two different HTML pages. I know it will be possible for the t

Answer 1

The usual way of addressing this is to have both scripts use flock() for locking:

$f = fopen('some_file', 'a');
flock($f, LOCK_EX);
fwrite($f, "some_line\n");
flock($f, LOCK_UN);
fclose($f);

This will cause the scripts to wait for each other to get done with the file before writing to it. If you like, the "less important" script can do:

$f = fopen('some_file', 'a');
if(flock($f, LOCK_EX | LOCK_NB)) {
    fwrite($f, "some_line\n");
    flock($f, LOCK_UN);
}
fclose($f);

so that it will just not do anything if it finds that something is busy with the file.