shm_get_var

(PHP 4, PHP 5, PHP 7, PHP 8)

shm_get_var — Returns a variable from shared memory

Description

shm_get_var(SysvSharedMemory $shm, int $key): mixed

shm_get_var() returns the variable with a given key, in the given shared memory segment. The variable is still present in the shared memory.

Parameters

shm: A shared memory segment obtained from shm_attach().
key: The variable key.

Return Values

Returns the variable with the given key.

Changelog

Version	Description
8.0.0	`shm` expects a SysvSharedMemory instance now; previously, a resource was expected.

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User Contributed Notes 6 notes

down

ricardophp at yahoo dot com dot br ¶

16 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();

?>

down

JM ¶

19 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!

down

hackmac at nowhere dot com ¶

15 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
    
?>

down

-1

Anonymous ¶

19 years ago

You will still receive a notice use @:

if(!defined(@shm_get_var($mutex, $mutex_key))) {
       shm_put_var($mutex, $mutex_key, 0);
}

down

-1

Bob Van Zant ¶

19 years ago

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);
}

down

-5

serg at red-sign dot ru ¶

11 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;
        }
?>

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shm_get_var

Description

Parameters

Return Values

Changelog

See Also

Found A Problem?

User Contributed Notes 6 notes