isEmpty() public method

public isEmpty ( )
 function Find($NodeStart, $NodeEnd)
 {
     $Queue = new PriorityQueue();
     // Open Nodes ordered based on F cost
     $Queue->setExtractFlags(PriorityQueue::EXTR_DATA);
     $Closed = 0;
     $Found = FALSE;
     $this->Debug = '';
     $this->Cache = array($NodeStart => array('G' => 0, 'F' => 0, 'Parent' => $NodeStart, 'Status' => STATUS_OPEN));
     $Queue->insert($NodeStart, $this->Cache[$NodeStart]['F']);
     while (!$Queue->isEmpty()) {
         $Node = $Queue->extract();
         if ($this->Cache[$Node]['Status'] == STATUS_CLOSED) {
             continue;
         }
         if ($Node == $NodeEnd) {
             $this->Cache[$Node]['Status'] = STATUS_CLOSED;
             $Found = TRUE;
             break;
         }
         if ($Closed > $this->Limit) {
             $this->Debug = 'Hit limit. (' . $this->Limit . ')';
             return NULL;
         }
         $Neighbours = $this->Graph->Neighbours($Node);
         foreach ($Neighbours as $Neighbour) {
             $G = $this->Cache[$Node]['G'] + $this->Graph->G($Node, $Neighbour);
             if (isset($this->Cache[$Neighbour]) && $this->Cache[$Neighbour]['Status'] && $this->Cache[$Neighbour]['G'] <= $G) {
                 continue;
             }
             $F = $G + $this->Graph->H($Neighbour, $NodeEnd);
             $this->Cache[$Neighbour] = array('G' => $G, 'F' => $F, 'Parent' => $Node, 'Status' => STATUS_OPEN);
             $Queue->insert($Neighbour, $F);
         }
         ++$Closed;
         $this->Cache[$Node]['Status'] = STATUS_CLOSED;
     }
     if ($Found) {
         $Path = array();
         $Node = $NodeEnd;
         while ($NodeStart != $Node) {
             $Path[] = $Node;
             $Node = $this->Cache[$Node]['Parent'];
         }
         $Path[] = $Node;
         return array_reverse($Path);
     }
     $this->Debug = 'Path not found, ran out of open nodes.';
     return NULL;
 }