ftok

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

ftok — Convert a pathname and a project identifier to a System V IPC key

说明

ftok ( string $filename , string $project_id ) : int

The function converts the filename of an existing accessible file and a project identifier into an integer for use with for example shmop_open() and other System V IPC keys.

参数

filename

Path to an accessible file.

project_id

Project identifier. This must be a one character string.

返回值

On success the return value will be the created key value, otherwise -1 is returned.

参见

User Contributed Notes

seelts at gmail dot com 13-Jan-2015 12:17
[email protected] has copied the code of [email protected]
But it is not correct.
The right version is here:
<?php
function ftok ($filePath, $projectId) {
    $fileStats = stat($filePath);
    if (!$fileStats) {
        return -1;
    }

    return sprintf('%u',
        ($fileStats['ino'] & 0xffff) | (($fileStats['dev'] & 0xff) << 16) | ((ord($projectId) & 0xff) << 24)
    );
}
?>

The difference is that $projectId string should be used as ASCII value via ord() function. Otherwise it will be interpreted as 0.
vlatko dot surlan at evorion dot hr 22-Apr-2013 10:09
The rather unintuitive usage of ftok with shm related functions like shmop_open and shm_attach could simply be explained as a need to avoid shm key collisions. Using ftok with a file that belongs to your project is likely to generate a unique key. Additionally, using ftok with a file from your project avoids the need to store the key so that other processes can access the segment because ftok will always give you the same key if you pass the same file.
Peter MOLNAR 18-May-2007 05:38
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.
marco at greenlightsolutions dot nl 17-Apr-2007 08:08
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.
mbowie at buzmo dot com 20-Oct-2004 02:41
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
abk at avatartechnology dot com 17-Jun-2004 01:17
Thanks to  [email protected] 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 at virusmedia dot de 26-May-2004 07:50
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
kimaz at swecom dot org 02-May-2004 06:35
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 at php dot net 24-Apr-2004 09:43
This function is not part neither of ext/sysvsem nor ext/sysvshm but comes with the core functions of PHP (from ext/standard).