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 $key;
}
ftok
(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
ftok — Преобразовывает путь и идентификатор проекта в ключ System V IPC
Описание
Функция преобразовывает путь filename существующего
доступного файла и идентификатор проекта в целое число для вызова,
например, в функции shmop_open() и других ключах System V IPC.
Список параметров
-
filename -
Путь к файлу
-
project_id -
Идентификатор проекта. Это должен быть один символ.
Возвращаемые значения
В случае успешного выполнения возвращает созданное значение ключа, и -1 в случае возникновения ошибки.
Смотрите также
- shmop_open() - Резервирование или использование блока разделяемой памяти
- sem_get() - Получение идентификатора семафора
add a note
User Contributed Notes 9 notes
abk at avatartechnology dot com ¶
20 years ago
vlatko dot surlan at evorion dot hr ¶
11 years ago
The rather unintuitive usage of ftok with shm related functions like shmop_open and shm_attach could simply be explained as a need to avoid shm key collisions. Using ftok with a file that belongs to your project is likely to generate a unique key. Additionally, using ftok with a file from your project avoids the need to store the key so that other processes can access the segment because ftok will always give you the same key if you pass the same file.
david dot rech at virusmedia dot de ¶
20 years ago
Missing ftok() on Windows? Here's my little workaround:
<?php
if( !function_exists('ftok') )
{
function ftok($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 $filename is empty, computed int as hex on success.
--
Regards,
David Rech
mbowie at buzmo dot com ¶
20 years ago
If you're planning to use ftok() to generate an IPC identifier to share with other applications, note that PHP uses the ASCII value of the proj parameter to generate the key, not the proj (aka id) parameter itself.
The result of this is that if you're using "1" as the id on the PHP side, you'll need to use 49 elsewhere.
This may not be the case under all OS's, but certainly is for FreeBSD which requires the id parameter passed to ftok to be an int.
Also of note, ipcs and ipcrm are extremely useful for debugging SysV queues etc.
References:
http://www.freebsd.org/cgi/man.cgi?query=ftok
http://www.asciitable.com
seelts at gmail dot com ¶
9 years ago
abk@avatartechnology.com has copied the code of daniele_dll@yahoo.it
But it is not correct.
The right version is here:
<?php
function ftok ($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.
marco at greenlightsolutions dot nl ¶
17 years ago
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.
kimaz at swecom dot org ¶
20 years ago
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 ¶
20 years ago
This function is not part neither of ext/sysvsem nor ext/sysvshm but comes with the core functions of PHP (from ext/standard).
Peter MOLNAR ¶
17 years ago
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.
