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ftok

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

ftokパス名とプロジェクト ID を、System V IPC キーに変換する

説明

ftok ( string $pathname , string $proj ) : int

この関数は、pathname で表される既存のアクセス可能なファイルおよびプロジェクト ID (proj) を、shmop_open() やその他で使用する System V IPC キーに変換します。

パラメータ

pathname

アクセ宇可能なファイルへのパス。

proj

プロジェクト ID。一文字からなる文字列でなければなりません。

返り値

成功した場合には作成されたキーの値を、それ以外の場合には -1 を返します。

参考

  • shmop_open() - 共有メモリブロックを作成またはオープンする
  • sem_get() - セマフォ ID を得る

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User Contributed Notes 9 notes

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9
abk at avatartechnology dot com
15 years ago
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;
}
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4
vlatko dot surlan at evorion dot hr
6 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.
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6
david dot rech at virusmedia dot de
15 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
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1
mbowie at buzmo dot com
14 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
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1
seelts at gmail dot com
4 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.
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1
marco at greenlightsolutions dot nl
12 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.
up
-1
kimaz at swecom dot org
15 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.
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-2
andreyKEINSPAM at php dot net
15 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).
up
-2
Peter MOLNAR
12 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.
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