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(PHP 4 >= 4.0.4, PHP 5)
shmop_open — Erstellt oder öffnet einen gemeinsamen Speicherblock
shmop_open() Kann einen gemeinsamen Speicherbereich erstellen oder öffnen.
Die System-ID des gemeinsam genutzten Speicherblocks, dieser Parameter kann als Dezimal- oder Hexadezimalzahl übergeben werden.
Folgende Flags können benutzt werden:
Die Zugriffsberechtigungen für die gemeinsamen Speichersegmente sind dieselben wie für Dateien. Diese Berechtigungen müssen als Oktalwerte übergeben werden, zum Beispiel 0644.
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.
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.
Beispiel #1 Einen neuen gemeinsamen Speicherblock erstellen
<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shmop_open($shm_key, "c", 0644, 100);
?>
In diesem Beispiel wurde ein gemeinsamer Speicherblock geöffnet. Die System-ID wurde von der Funktion ftok() zurückgegeben.
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->filepointer, LOCK_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 $data;
}
}
?>
=== Checking if a shared memory exists ===
The solution provided by Mitchell_Shnier at ieee dot orgZ doesn't work on my computer - I get a warning "Invalid flag ac".
In order to check if a shared-memory exists, you just have to open it with the "a" or "w" flag, while hiding the warnings using the "@" operator:
<?php
@$shid = shmop_open($systemId, "a", 0666, 0);
if (!empty($shid)) {
... shared memory exists
} else {
... shared memory doesn't exist
}
?>
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
Just an alternative idea if 'shared memory' is what you need for your websites, you can use tmpfs (on Linux):
Get root to do this:
mkdir /home/myname/tmpfs
chown myname:mygroup /home/myname/tmpfs
..and this in a script executed at boot time:
mount -t tmpfs /mnt/tmpfs /home/myuser/tmpfs
Now you can use regular file functions (including locking) to access shared memory between all your processes.
More info: http://docsun.cites.uiuc.edu/sun_docs/C/
...and this because the note editor doesn't accept long lines...
solaris_9/SUNWaadm/SYSADV1/p150.html
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 :)
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.
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.
the key is a LONG variable type, meaning that the key can only be eight (8) bytes long, which can be too short if you're using any form of automagic key generation (like a parsed filename)
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