shmop_open

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

shmop_open — Crea o abre un bloque de memoria compartida

Descripción

shmop_open(
    int $key,
    string $mode,
    int $permissions,
    int $size
): Shmop|false

shmop_open() puede crear o abrir un bloque de memoria compartida.

Parámetros

key

Identificador del sistema para el bloque de memoria compartida. Este argumento puede ser pasado como un decimal o un hexadecimal.

mode

Se pueden utilizar:

"a" para acceso (utiliza SHM_RDONLY para shmat) utilice esta opción para abrir un bloque ya existente en modo solo lectura.
"c" para creación (utiliza IPC_CREATE) utilice esta opción para crear un nuevo bloque, o, si un segmento con el mismo identificador existe, intentar acceder a él en modo lectura y escritura.
"w" para acceso en lectura y escritura. Utilice esta opción cuando se deba acceder en lectura y escritura a un segmento de memoria compartida. Este es el caso más común.
"n" crea un nuevo segmento de memoria compartida (utiliza IPC_CREATE|IPC_EXCL). Utilice esta opción cuando se quiera crear un nuevo segmento de memoria compartida a menos que ya exista uno corrupto con la misma opción. Esto es muy útil por razones de seguridad, para evitar agujeros de seguridad que exploten la carrera por los recursos.

permissions

Los permisos que se otorgan a este bloque. Son los mismos que para los archivos. Estos permisos deben ser pasados en formato octal (i.e. 0644).

size

El tamaño del bloque de memoria compartida que se quiere crear, en bytes

Nota:
Nota: Los tercer y cuarto argumentos deben ser pasados a 0 si se quiere abrir un bloque de memoria compartida ya existente.

Valores devueltos

En caso de éxito, shmop_open() devuelve una instancia de Shmop que puede ser utilizada para acceder a la memoria que se acaba de crear. false será devuelto en caso de fallo.

Errores/Excepciones

Si mode es inválido, o si size es inferior o igual a cero, se lanza una ValueError. En otros casos de fallo, se emite un E_WARNING.

Historial de cambios

Versión	Descripción
8.0.0	`shmop` ahora espera una instancia de Shmop anteriormente se esperaba un resource.
8.0.0	Si `mode` es inválido, o si `size` es inferior o igual a cero, se lanza una ValueError; anteriormente, se emitía un `E_WARNING` en su lugar, y la función devolvía `false`.

Ejemplos

Ejemplo #1 Crear un nuevo bloque de memoria compartida Shmop

<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shmop_open($shm_key, "c", 0644, 100);
?>

Este ejemplo abre un nuevo bloque de memoria compartida, cuyo identificador es devuelto por ftok().

Ver también

shmop_close() - Cierra un bloque de memoria compartida
shmop_delete() - Destruye un bloque de memoria compartida

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User Contributed Notes 9 notes

down

kakkau at grr dot la ¶

9 years ago

On *nix systems shmop_open is able to create an "infinite" amount of segments when setting $key = 0.

After executing the following command twice in an interactive shell
php > $res = shmop_open(0,"n",0600,1024);

list the memory segments currently present 
$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 2293762    user       600        1024       0
0x00000000 2326531    user       600        1024       0

For any integer <> 0 in conjunction with the flag "n" shmop_open works like documented. It fails.

down

daniele_dll at yahoo dot it ¶

21 years ago

There is a little ftok function. This function isn't included into php for windows so i've grabbed it directly from linux glibc 2.3.2 source code. I hope that this can be useful.
There is the code:

<?php
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;
}

echo ftok($_SERVER["SCRIPT_FILENAME"], 250);
?>

sorry for my english :)

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Craig Manley ¶

20 years ago

To: macmaster at pobox dot com:

To clear up some new confusion: you said the shm key is 8 bytes long. As far as I know it's 4 bytes (32bits).
Check out the output of ipcs on Linux below to see what I mean.

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status      
0x6e6a694d 65538      mijnbel   644        65536      0                       
0x326e794d 98307      mijnbel   644        65536      0                       
0x62417347 131076     smsklap   644        65536      0

down

kakkau at grr dot la ¶

7 years ago

One is not able to reconnect to a segment with key 0. For any other key (e.g. 1) the flags just work fine.

php > $soid = shmop_open(0,"n",0600,10);
php > $soid = shmop_open(0,"w",0600,10);
PHP Warning:  shmop_open(): unable to attach or create shared memory segment 'Invalid argument' in php shell code on line 1
PHP Stack trace:
PHP   1. {main}() php shell code:0
PHP   2. shmop_open(0, 'w', 384, 10) php shell code:1

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Filippo Fadda ¶

10 years ago

I'm having the same issue affecting XP and described below, on Mac OS X Lion.

To solve it, use before 'a' flag, then 'n'. Avoid 'c' flag.

<?php
$str = 'Hello World';

shm_key = ftok($_SERVER['PHP_SELF']);

if (@$shm_id = shmop_open($shm_key, 'a', 0644, 0))
  shmop_delete($shm_id);

$shm_id = shmop_open($shm_key, 'n', 0644, strlen($str));

if ($shmId) {
  shmop_write($shmId, $str, 0);
  shmop_close($shmId);
}
else
  throw new RuntimeException("Couldn't create shared memory segment.");
?>

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thanks at forthefish dot com ¶

11 years ago

These shared memory functions are kind of silly on Windows where sem_get() and friends nor any sort of synchronization object is available (as of PHP 5.5.5) to perform proper locking prior to access.  A core PHP dev needs to write some wrappers for sem_get() for Windows as they did for shmop to really round out this feature.

The implementation of shmop for Windows is pretty slick - the author basically ported variations of POSIX functions to Windows equivalent prototypes.

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erelsgl at gmail dot com ¶

17 years ago

=== Checking if a shared memory exists ===
The solution provided by Mitchell_Shnier at ieee dot orgZ doesn't work on my computer - I get a warning "Invalid flag ac".

In order to check if a shared-memory exists, you just have to open it with the "a" or "w" flag, while hiding the warnings using the "@" operator:
<?php
@$shid = shmop_open($systemId, "a", 0666, 0);
if (!empty($shid)) {
            ... shared memory exists
} else {
            ... shared memory doesn't exist
}
?>

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Chris Petersen ¶

21 years ago

Be warned that if you try to shmop_open with a key set to zero, shmop_open will seemingly work, and you can write to it, but you will not be able to read from it or delete it.  If you're not careful, you can continue doing this - creating more and more shared memory blocks at "zero" until eventually you WILL start getting errors saying that php can't access or create the shared memory block, and you will have to restart your machine to free up all of those "zero" blocks.

down

-1

Colin Paterson ¶

9 years ago

If you are running your main script as say user "root" but need to open a Shared Memory Segment as another user (from your main script) such as say "www-data" then this works:

exec("sudo -u www-data php -r 'shmop_open(0xee4, "c", 0770, 100);'"); //Create Shared Memory segment as USER www-data

$SharedMemorySegment = shmop_open(0xee4, "c", 0770, 100); 
        if (!$SharedMemorySegment) {
            echo "Couldn't create shared memory segment\n";
        }

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