|
|
|
|
Bookmark this on Delicious
Share on Facebook
 Slashdot It!
Digg  ftok
Convert a pathname and a project identifier to a System V IPC key
(PHP 4 >= 4.2.0, PHP 5)
Code Examples / Notes » ftokkimaz
You dont have to use ftok() for specifying an System V IPC identifier, though its a good thing to do so. Passing a regular int to, e.g. msg_get_queue, will have the same effect aslong as you use that value when reading/writing. I use it for some minor tasks generating small queue's. andreykeinspam
This function is not part neither of ext/sysvsem nor ext/sysvshm but comes with the core functions of PHP (from ext/standard).
abk
Thanks to daniele_dll@yahoo.it who got this in turn from linux glibc 2.3.2: http://www.php.net/manual/en/function.shmop-open.php -- I'm putting this here because it might be helpful to others. function ftok($pathname, $proj_id) { $st = @stat($pathname); if (!$st) { return -1; } $key = sprintf("%u", (($st['ino'] & 0xffff) | (($st['dev'] & 0xff) << 16) | (($proj_id & 0xff) << 24))); return $key; } david dot rech
Missing ftok() on Windows? Here's my little workaround: <?php if( !function_exists('ftok') ) { function ftok($filename = "", $proj = "") { if( empty($filename) || !file_exists($filename) ) { return -1; } else { $filename = $filename . (string) $proj; for($key = array(); sizeof($key) < strlen($filename); $key[] = ord(substr($filename, sizeof($key), 1))); return dechex(array_sum($key)); } } }?> NOTE: There *may* be duplicate keys, even if probability is low. The key's were NOT computed like the original UNIX ftok() because i.e. fileinode() is also missing on windows. Normally ftok() computes a key based on the file inode and the system minor id of the harddrive the file resides. Behaviour is like PHPs ftok(), -1 is returned if file is missing or $filename is empty, computed int as hex on success. -- Regards, David Rech peter molnar
mbowie at buzmo dot com wrote: "The result of this is that if you're using "1" as the id on the PHP side, you'll need to use 49 elsewhere." You can always use chr() as an alternative. mbowie
If you're planning to use ftok() to generate an IPC identifier to share with other applications, note that PHP uses the ASCII value of the proj parameter to generate the key, not the proj (aka id) parameter itself. The result of this is that if you're using "1" as the id on the PHP side, you'll need to use 49 elsewhere. This may not be the case under all OS's, but certainly is for FreeBSD which requires the id parameter passed to ftok to be an int. Also of note, ipcs and ipcrm are extremely useful for debugging SysV queues etc. References: http://www.freebsd.org/cgi/man.cgi?query=ftok http://www.asciitable.com marco
As ftok uses only the last 16 bits of the inode of the file, you can get collisions on large filesystems. Unfortunately, on large filesystems you can get collisions rather quickly: if you have a collection of 350-400 files, odds are that two of them have inodes with the same last 16 bits. So I've taken to using fileinode instead of ftok with functions like shmop_open.
|
