shm_get_var()

(PHP 4, PHP 5, PHP 7)

Returns a variable from shared memory

说明

shm_get_var(resource $shm_identifier,int $variable_key): mixed

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

参数

$shm_identifier: Shared memory segment, obtained from shm_attach().
$variable_key: The variable key.

返回值

Returns the variable with the given key.

参见

shm_has_var()Check whether a specific entry exists
shm_put_var()Inserts or updates a variable in shared memory

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
  
?>

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();
?>

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!

You will still receive a notice use @:
if(!defined(@shm_get_var($mutex, $mutex_key))) {
    shm_put_var($mutex, $mutex_key, 0);
}

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);
}

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;
    }
?>

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