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.

    See Also

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    User Contributed Notes 6 notes

    up
    2
    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();
    ?>
    up
    1
    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!
    up
    0
    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

    ?>
    up
    -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);
    }
    up
    -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);
    }
    up
    -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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