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This document uses PHP Chinese website manual Release
(PHP 4 >= 4.0.4, PHP 5)
shmop_open — Create or open shared memory block
$key
, string $flags
, int $mode
, int $size
)shmop_open() can create or open a shared memory block.
key
System's id for the shared memory block. Can be passed as a decimal or hex.
flags
The flags that you can use:
mode
The permissions that you wish to assign to your memory segment, those are the same as permission for a file. Permissions need to be passed in octal form, like for example 0644
size
The size of the shared memory block you wish to create in bytes
Note:
Note: the 3rd and 4th should be entered as 0 if you are opening an existing memory segment.
On success shmop_open() will return an id that you can
use to access the shared memory segment you've created. FALSE
is
returned on failure.
Example #1 Create a new shared memory block
<?php
$shm_key = ftok ( __FILE__ , 't' );
$shm_id = shmop_open ( $shm_key , "c" , 0644 , 100 );
?>
This example opened a shared memory block with a system id returned by ftok() .
[#1] Colin Paterson [2015-09-17 20:14:55]
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";
}
[#2] Filippo Fadda [2015-02-27 17:37:39]
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.");
?>
[#3] thanks at forthefish dot com [2013-10-28 06:24:10]
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.
[#4] a [2011-02-25 16:31:00]
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);
?>
[#5] DinosauRUS [2008-08-29 03:24:05]
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 $data;
}
}
?>
[#6] erelsgl at gmail dot com [2007-11-27 03:04:14]
=== Checking if a shared memory exists ===
The solution provided by Mitchell_Shnier at ieee dot orgZ doesn't work on my computer - I get a warning "Invalid flag ac".
In order to check if a shared-memory exists, you just have to open it with the "a" or "w" flag, while hiding the warnings using the "@" operator:
<?php
@$shid = shmop_open($systemId, "a", 0666, 0);
if (!empty($shid)) {
... shared memory exists
} else {
... shared memory doesn't exist
}
?>
[#7] Craig Manley [2005-01-05 17:19:33]
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
[#8] daniele_dll at yahoo dot it [2004-02-01 13:28:09]
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 :)
[#9] Chris Petersen [2003-08-28 11:18:54]
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.
[#10] Mitchell_Shnier at ieee dot orgZ [2001-11-07 17:51:21]
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.