PHP 5.4.36 Released

shmop_open

(PHP 4 >= 4.0.4, PHP 5)

shmop_openErstellt oder öffnet einen gemeinsamen Speicherblock

Beschreibung

int shmop_open ( int $key , string $flags , int $mode , int $size )

shmop_open() Kann einen gemeinsamen Speicherbereich erstellen oder öffnen.

Parameter-Liste

key

Die System-ID des gemeinsam genutzten Speicherblocks, dieser Parameter kann als Dezimal- oder Hexadezimalzahl übergeben werden.

flags

Folgende Flags können benutzt werden:

  • "a" zum Zugriff (access) auf einen gemeinsamen Speicherblock (setzt SHM_RDONLY für shmat). Benutzen Sie dieses Flag, wenn Sie einen bestehenden gemeinsamen Speicherblock nur zum Lesen öffnen wollen.
  • "c" zum Erzeugen (create) eines gemeinsamen Speicherblocks (setzt IPC_CREATE). Benutzen Sie dieses Flag, wenn Sie einen neuen gemeinsamen Speicherblock erzeugen wollen oder, falls bereits ein Segment mit derselben ID existiert, zum Öffnen dieses Segments für Lese- und Schreibzugriffe.
  • "w" für Lese- und Schreibzugriffe. Benutzen Sie dieses Flag wenn Sie in einen gemeinsamen Speicherbereich schreiben oder daraus lesen müssen. Das wird meistens der Fall sein.
  • "n" zum Erzeugen eines neuen gemeinsamen Speichersegments (setzt IPC_CREATE|IPC_EXCL). Benutzen Sie dieses Flag, wenn Sie ein neues gemeinsames Speichersegment erzeugen wollen. Falls schon ein Segment mit diesem Flag existiert, schlägt die Funktion fehl. Dies ist aus Sicherheitsgründen nützlich, denn damit können Sie vermeiden, dass konkurrierende Prozesse ausgenutzt werden.

mode

Die Zugriffsberechtigungen für die gemeinsamen Speichersegmente sind dieselben wie für Dateien. Diese Berechtigungen müssen als Oktalwerte übergeben werden, zum Beispiel 0644.

size

Die Größe des erzeugten gemeinsam genutzten Speicherbereichs in Byte.

Hinweis:

Beachten Sie: der dritte und vierte Parameter sollten mit 0 angegeben sein, falls Sie einen bereits existierenden Speicherbereich öffnen.

Rückgabewerte

Bei Erfolg liefert die Funktion shmop_open() eine ID zurück, die Sie zum Zugriff auf den erstellten gemeinsamen Speicher benutzen können. Bei einem Fehler wird FALSE zurückgegeben.

Beispiele

Beispiel #1 Einen neuen gemeinsamen Speicherblock erstellen

<?php
$shm_key 
ftok(__FILE__'t');
$shm_id shmop_open($shm_key"c"0644100);
?>

In diesem Beispiel wurde ein gemeinsamer Speicherblock geöffnet. Die System-ID wurde von der Funktion ftok() zurückgegeben.

Siehe auch

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User Contributed Notes 8 notes

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1
erelsgl at gmail dot com
7 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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1
thanks at forthefish dot com
1 year 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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1
Craig Manley
9 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
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0
a
3 years ago
On win xp 32bit php 5.2.6 recreation of shared memory block with the same id but bigger size fails.

<?php
$shm_key
= 0xff3;
$shm_id = shmop_open($shm_key, "c", 0666, 128);
shmop_delete($shm_id);
shmop_close($shm_id);
$shm_id = shmop_open($shm_key, "c", 0666, 32);
shmop_delete($shm_id);
shmop_close($shm_id);
$shm_id = shmop_open($shm_key, "c", 0666, 1024); // on win32 fails there
shmop_delete($shm_id);
shmop_close($shm_id);
?>
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0
DinosauRUS
6 years ago
If you faced with any problem you're going to solve with shared memmory, but your server doesn't support it, you can use files instead. I've wrote simple wrapper for this and its suites for me. Hope it will be usefull for you too.

<?php

define
(kSHARED_FOLDER, "shared/");
define(kSHARED_MAX_ATTEMPS, 10);
define(kSESSION_SHARED, "shared_");

class
Shared {
    var
$id = 0;
    var
$filename = '';
    var
$filepointer;
   
    var
$data = array();
    var
$date = 0;
   
    function
Shared($id) {
       
$this->id = $id;
       
       
$this->filename = kSHARED_FOLDER.$this->id;
       
        if(empty(
$this->filename))
        {
            print
"no filename";
            return
false;       
        }
       
       
$this->date = $_SESSION[kSESSION_SHARED.$id];
           
    }
   
    function
clear() {
        if (
$this->id == null)
        {
            return
false;
        }
           
       
$counter = 0;
       
ignore_user_abort(true);
        if((
$this->filepointer = @fopen($this->filename, "w")) == false) {       
           
ignore_user_abort(false);
            return
false;
        }

        while(
true) {
            if (
$counter >= kSHARED_MAX_ATTEMPS) {
               
fclose($this->filepointer);
               
ignore_user_abort(false);
                return
false;
            }
           
            if(
flock($this->filepointer, LOCK_EX) == false) {
               
$counter++;
               
usleep(rand(1, 25000));
            }
            else
                break;
        }

        if(
flock($this->filepointer, LOCK_UN) == false) {       
           
ignore_user_abort(false);
            return
false;
        }
       
        unset(
$this->data);
       
$this->data = array();

       
fclose($this->filepointer);
       
$this->date = $_SESSION[kSESSION_SHARED.$id] = filemtime($this->filename);
       
ignore_user_abort(false);
       
        return
true;
    }
   
    function
setObjectForKey($value, $key) {
        if (
$this->id == null)
            return
false;
           
       
$counter = 0;
       
ignore_user_abort(true);
        if((
$this->filepointer = @fopen($this->filename, "a+")) == false) {       
           
ignore_user_abort(false);
            print
"can not open file<br>";
            return
false;
        }

        while(
true) {
            if (
$counter >= kSHARED_MAX_ATTEMPS) {
               
fclose($this->filepointer);
                print(
"1 aborted...");
               
ignore_user_abort(false);
                return
false;
            }
           
           
$block;
            if(
flock($this->filepointer, LOCK_EX, $block) == false) {
               
$counter++;
                print(
"1 waiting...");
               
usleep(rand(1, 25000));
            }
            else
                break;
        }
       
       
$data = file_get_contents($this->filename);
       
$array = array();
        if (!empty(
$data))
           
$array = unserialize($data);

       
$array[$key] = $value;
       
$data = serialize($array);
       
ftruncate($this->filepointer, 0);
       
fseek($this->filepointer, 0, SEEK_SET);
       
fwrite($this->filepointer, $data);
       
       
$this->data = $array;
       
        if(
flock($this->filepointer, LOCK_UN) == false) {       
           
ignore_user_abort(false);
            return
false;
        }

       
fclose($this->filepointer);
       
$this->date = $_SESSION[kSESSION_SHARED.$id] = filemtime($this->filename);
       
ignore_user_abort(false);
       
        return
true;
    }
   
    function
getObjectForKey($key)    {
        if (
$this->id == null)
            return
null;
           
       
$counter = 0;
       
ignore_user_abort(true);
   
        if((
$this->filepointer = @fopen($this->filename, "a+")) == false) {       
           
ignore_user_abort(false);
            print(
"can not open<br>");
            return
null;
        }

        if (
$this->date == filemtime($this->filename)) {           
           
fclose($this->filepointer);
            return
$this->data[$key];
        }
       
        while(
true) {
            if (
$counter >= kSHARED_MAX_ATTEMPS) {
               
fclose($this->filepointer);
               
ignore_user_abort(false);
                print(
"2 aborted<br>");
                return
null;
            }
           
            if(
flock($this->filepointerLOCK_SH ) == false) {
               
$counter++;
                print(
"2 waiting...<br>");
               
usleep(rand(1, 25000));
            }
            else
                break;
        }
       
       
fseek($this->filepointer, 0);
       
$data = file_get_contents($this->filename);
       
$array = array();
        if (!empty(
$data))
           
$array = unserialize($data);
           
       
$data = $array[$key];
       
$this->data = $array;
       
        if(
flock($this->filepointer, LOCK_UN) == false) {       
           
ignore_user_abort(false);
            return
$data;
        }

       
fclose($this->filepointer);
       
$this->date = $_SESSION[kSESSION_SHARED.$id] = filemtime($this->filename);
       
ignore_user_abort(false);
       
        return
$data;
    }
}
?>
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0
Chris Petersen
11 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.
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-2
daniele_dll at yahoo dot it
10 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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-1
Mitchell_Shnier at ieee dot orgZ
13 years ago
To check whether a particular shared memory segment is already created, you need to concatenate the "a" and "c" flags. For example (where $SystemKey is the Unix key used by the other process(es) with which you want to share this memory segment)...<BR>
$shm_id = shmop_open($SystemKey, "ac", 0, 0);
if ($shm_id) {
   #it is already created
} else {
   #you need to create it with shmop_open using "c" only
}<BR>
Using only "a" does not work (just as using only IPC_EXCL in the Unix shmget() call is meaningless). Also, use the ipcs shell command to see your shared memory segments.
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