besides from what the manual says about locking a file opendend in w or w+ and using a special lock file for these cases, you should simply truncate the file yourself with ftruncate() after writing:
<?php
$data='some data';
$handle=fopen('file','r+');
flock($handle,LOCK_EX);
fwrite($handle,$data);
ftruncate($handle,ftell($handle));
flock($handle,LOCK_UN);
fclose($handle);
?>
now the file will have the size of $data without opening the file in w mode but with a lock on the file.
to the previous writers jpriebe and mallory:
of course the lock is lost in this case, but thats simply because the file is closed by PHP. and closing the file means unlocking it (same as when you use fclose() yourself).
