Magento Irregular caching of my custom block

Question

I have created a custom block to display 10 random products on my homepage, and for load time etc, it is a bad idea to request random products from the database each load. Thus, have incorporated the default magento caching mechanism into my code to cache x versions of the block and rotate them for each user. But, I cannot get it to work correctly.

Currently, it loads random products A, B and C on first page load. Then loads new different random products ( products X, Y & Z) on the next page load. The page load after that loads the random products from the first load (A,B & C).

I cannot see where I have gone wrong thus was wondering if anyone could kindly help myself see my mistake.

Code,

    <?php
    class Vish_RandomProduct_Block_Random extends Mage_Core_Block_Template{
            protected function _construct()
    {
        $this->addData(array(
            'cache_lifetime' => 86400,
            'cache_tags'=> array(Mage_Core_Model_Store::CACHE_TAG, Mage_Cms_Model_Block::CACHE_TAG)
        ));
    }
protected function _getRandomProductCollection()
{
    $numberOfItems = 12;

$productCollection = Mage::getModel('catalog/product')->getCollection()
    ->addStoreFilter()
    ->setVisibility(Mage::getSingleton('catalog/product_visibility')->getVisibleInCatalogIds())
    ->addAttributeToFilter('name', array('nlike' => '%Adjustable Book Protection Jackets%'));
$candidateIds = $productCollection->getAllIds();
$numberOfProducts = count($candidateIds);
$chosenIds = [];
while ($numberOfItems) {
    $randomKey = mt_rand(0, $numberOfProducts - 1);
    if (!isset($chosenIds[$randomKey])) {
        $chosenIds[$randomKey] = $candidateIds[$randomKey];
        --$numberOfItems;
    }
}
$productCollection->addIdFilter($chosenIds);
$productCollection
    ->addMinimalPrice()
    ->addFinalPrice()
    ->addTaxPercents()
    ->addAttributeToSelect(Mage::getSingleton('catalog/config')->getProductAttributes())
    ->addUrlRewrite();

    return $productCollection;
}
public function getCacheKeyInfo()
{
  $session = Mage::getSingleton('core/session');
  $counter = $session->getData('random_counter');
  $counter = ($counter + 1) % 10;
  $session->setData('random_counter', $counter);
  return array(
    $this->getNameInLayout(),
    $counter
  );
}
}
?>

Update:-

investigating further, via the placement of a mage::log, to see the count variable in the getCacheKeyInfo() function it reveals 3 entries each time I refresh. Little confused why this function is running this many times.

2017-11-21T20:11:45+00:00 DEBUG (7): 1 2017-11-21T20:11:45+00:00 DEBUG (7): 2 2017-11-21T20:11:45+00:00 DEBUG (7): 3

Rest of the block code:

vishrandom.phtml

    <?php
$collection = $this->_getRandomProductCollection(); 
//  Mage::log("template for random called", null, 'randomprodcachelog.log');
?>
<?php if ($collection->getSize() > 0): ?>
     <div class="jcarousel-wrapper">
                <div class="jcarousel">
                    <ul>
                           <?php foreach ($collection as $_product) {  ?>

                        <li><a href="<?php echo $_product->getProductUrl() ?>">
                        <img src='media/wysiwyg/805.svg' data-src="<?php echo $this->helper('catalog/image')->init($_product, 'small_image')->resize(200); ?>" alt="" /></a> 

                        <div class="productName">

                        <a href="<?php echo $_product->getProductUrl(); ?>"><?php echo $_product->getName(); ?></a><br/>
                        </div> 
                        <?php if($this->htmlEscape($_product->getExtraInfo() !="")):?>
                            <span class="icon icon-info-circle tooltip" title="<?php echo $this->htmlEscape($_product->getExtraInfo())?>" ></span>
                            <?php endif;?>

                        <div class="productCode">
                    <?php echo $this->__('Product Code: ') . $this->htmlEscape($_product->getData('sku'));?>
                    </div>                      
                         <?php if($_product->isSaleable()): ?>
                        <p><button type="button" title="<?php echo $this->__('Add to Cart') ?>" class="button btn-cart" onclick="setLocation('<?php echo $this->helper('checkout/cart')->getAddUrl($_product) ?>')"><span><span><?php echo $this->__('Add to Basket') ?></span></span></button></p>
                    <?php else: ?>
                        <p class="availability out-of-stock"><span><?php echo $this->__('Out of stock') ?></span></p>
                    <?php endif; ?>

                    <ul class="add-to-links">
                        <?php if ($this->helper('wishlist')->isAllow()) : ?>
                            <li><a href="<?php echo $this->helper('wishlist')->getAddUrl($_product) ?>" class="link-wishlist"><?php echo $this->__('Add to Wishlist') ?></a></li>
                        <?php endif; ?>

                    </ul>

                        </li>
                         <?php }?>
                    </ul>
                </div>

                <a href="#" class="jcarousel-control-prev">&lsaquo;</a>
                <a href="#" class="jcarousel-control-next">&rsaquo;</a>


            </div>

<?php endif;?>

/local/vish/RandomProduct/etc/config.xml

<?xml version="1.0"?>
<config>
<modules>
<Vish_RandomProduct>
<version>0.0.1</version>
</Vish_RandomProduct>
</modules>
<global>
    <blocks>
      <Vish_RandomProduct>
                <class>Vish_RandomProduct_Block</class>
      </Vish_RandomProduct>
    </blocks>
    </global>
</config>

Answer 1

Solution 1:

protected function _construct()
{
    $this->addData(array(
    'cache_lifetime' => 3600,
    'cache_tags'     => array(Mage_Catalog_Model_Product::CACHE_TAG),
    'cache_key'      => $this->getProduct()->getId(),
    ));
}

Solution 2:

<your_layout_handle>
    <reference name="root">
        <block type="type/block" name="my.block" template="path/to/bock.phtml">
           <action method="setCacheLifetime"><lifetime>3600</lifetime></action>
       </block>
    </reference>
</your_layout_handle>