This seems to work fine to detect the lack of presence of a key in shared memory and then init it to 0 when found:
if(!defined(shm_get_var($mutex, $mutex_key))) {
shm_put_var($mutex, $mutex_key, 0);
}
shm_get_var
(PHP 4, PHP 5, PHP 7)
shm_get_var — Devuelve una variable desde la memoria compartida
Descripción
shm_get_var() devuelve la variable con la clave dada por
variable_key, del segmento de memoria compartida dado.
La variable todavía está presente en la memoria compartida.
Parámetros
-
shm_identifier -
Segmento de memoria compartida, obtenido desde shm_attach().
-
variable_key -
La clave de la variable.
Valores devueltos
Devuelve la variable con la clave dada.
Ver también
- shm_has_var() - Verificar si existe una entrada específica
- shm_put_var() - Inserta o actualiza una variable en la memoria compartida
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User Contributed Notes 7 notes
Bob Van Zant ¶
15 years ago
ricardophp at yahoo dot com dot br ¶
12 years ago
A fully functional sample ...
<?php
echo "<PRE>\n";
define("FOPEN_RESOURCE", 1);
$shm_id = shm_attach(FOPEN_RESOURCE);
if ($shm_id === false) {
exit("Fail to attach shared memory.\n");
}
$fopen_resource = fopen("/tmp/phpSharedMemory.bin", "w");
$a = array("Teste1", 1);
if (!shm_put_var($shm_id, $a, $a)) {
exit("Failed to put var 1 in shared memory $shm_id.\n");
}
echo "F: ".$a[0].":".$a[1]."\n";
$pid = pcntl_fork();
if($pid == -1) {
die("could not fork\n");
}
else if ($pid) {
$a = array("Teste2", 3);
if (!shm_put_var($shm_id, $a, $a)) {
exit("Failed to put var 1 in shared memory $shm_id.\n");
}
echo "P1: ".$a[0].":".$a[1]."\n";
} else {
sleep(2);
$a = shm_get_var($shm_id, $a);
echo "P2: ".$a[0].":".$a[1]."\n";
}
pcntl_wait($status);
exit();
?>
hackmac at nowhere dot com ¶
11 years ago
hello everyone i came up with some sort of solution to the shm_get_var()
returns false on error/returns a boolean false variable problem.
test script
<?php
error_reporting(E_ALL);
ini_set('display_errors', '1');
echo '<pre>';
echo ini_get('sysvshm.init_mem');
require_once('ClassShmWrapper.php5');
$nKey = ftok(__FILE__,'x');
$myShm = new ClassShmWrapper($nKey);
$myShm->attachToSegment();
#$mValue = range(1,rand(3,10));
#$myShm->nVarKey = count($mrValue);
#$mValue = FALSE;
/*
$mValue = TRUE;
$myShm->nVarKey = 1;
$myShm->mVar = $mValue;
$myShm->putVarToSegment();
*/
#$myShm->nVarKey = 2;
$myShm->nVarKey = 1;
if ($myShm->getVarFromSegment()) {
echo "found var in shm\n";
}
else {
echo "could NOT find var in shm\n";
}
$myShm->detachFromSegment();
echo "\ndumping " . '$myShm->mVar' . "\n";
var_dump($myShm->mVar);
?>
class for using the shm_ functions & class for storing boolean values
<?php
class ClassShmWrapper {
public $nPermissions;
public $nKey;
public $nBytesMemorySize;
public $nShmId;
public $nVarKey;
public $mVar;
public function __construct($nKey,$nBytesMemorySize=50000,$nPermissions=0666) {
$this->nKey = $nKey;
$this->nBytesMemorySize = $nBytesMemorySize;
$this->nPermissions = $nPermissions;
}
public function attachToSegment() {
$this->nShmId = shm_attach($this->nKey,$this->nBytesMemorySize,$this->nPermissions);
}
public function detachFromSegment() {
shm_detach($this->nShmId);
}
public function removeSegment() {
shm_remove($this->nShmId);
}
public function getVarFromSegment() {
$mVar = NULL;
if (($mVar = @shm_get_var($this->nShmId,$this->nVarKey)) !== FALSE) {
$this->mVar = $mVar;
unset($mVar);
/*
For variables of type boolean we need to access an object property which stores the boolean value.
This is needed as shm_get_var() could return FALSE when returning a boolean variable set to FALSE
or when a non-existing variable key was tried to access!
*/
if ($this->mVar instanceof ClassShmBooleanWrapper) {
$this->mVar = $this->mVar->bVal;
}
return TRUE;
}
else {
return FALSE;
}
}
/**
* Puts a PHP variable into shared memory (or updates an existing one for the given variable key).
*
* @return boolean returns TRUE on success/FALSE on error
*/
public function putVarToSegment() {
// cmp -> comment getVarFromSegment()
if (is_bool($this->mVar)) {
return shm_put_var($this->nShmId,$this->nVarKey,new ClassShmBooleanWrapper($this->mVar));
}
else {
return shm_put_var($this->nShmId,$this->nVarKey,$this->mVar);
}
}
public function removeVarFromSgement() {
shm_remove_var($this->nShmId,$this->nVarKey);
}
} // end class
class ClassShmBooleanWrapper {
public $bVal;
public function __construct($bVal) {
$this->bVal = $bVal;
}
} // end class
?>
JM ¶
15 years ago
To follow up on the posts by anonymous, Bob Van Zant and chris at free-source dot com below (or, as must people inexplicably write, above) regarding the PHP warning and FALSE that shm_get_var returns if the variable key doesn't exist:
My tests (with PHP4.3.4) show that defined() is useless here. Because the function defined(string) checks whether the constant whose name is string exists, the code
<?php
if ( defined(@shm_get_var($mutex, $mutex_key)) {
...
}
?>
acts the same ("..." does not get executed) whether the variable is defined or not--unless $mutex_key happens to identify a valid string that happens to be the name of a constant. :)
Rather,
<?php
if ( @shm_get_var($mutex, $mutex_key) === FALSE ) {
...
}
?>
works, provided the object that was stored isn't actually FALSE (via <?php shm_put_var($mutex, $mutex_key, FALSE); ?>)
It would be nice to have a completely air-tight solution, though. D'oh!
Anonymous ¶
15 years ago
You will still receive a notice use @:
if(!defined(@shm_get_var($mutex, $mutex_key))) {
shm_put_var($mutex, $mutex_key, 0);
}
serg at red-sign dot ru ¶
7 years ago
If any body has problem with shm_get_var();
this code correctly work with boolean-values^
<?php
if(shm_has_var ($this->shm_mem_id, $_varno)){
$_value = shm_get_var($this->shm_mem_id, $_varno);
}else{
$_value = NULL;
}
?>
php at pharse dot com ¶
11 years ago
I was annoyed by this warning when using shm_get_var():
Warning: shm_get_var() [function.shm-get-var]: variable key 2 doesn't exist in PATH_TO_FILE on line 64.
You can suppress the warning by changing the error reporting level. To do this for just the page in question, include the following line:
<?php
error_reporting(E_ERROR);
?>
For more info: http://us.php.net/error_reporting
