How to use cache set and get to store time cron ran?

Question

We have a new requirement where we need to run a job on a daily basis. We have setup cron to run every 1 hour. The goal is to have cron ron every 1 hour, but we want a specific job to run only if 1 day (24hours) has past since last run.

We used to use the Variables table to store the time the job was last run, but we need to change this to use the cache table. Below is the code (mymodule.module) we were reviewing, but it is not creating a cache table and not storing the appropriate date. So we need assistance in figuring out if we are using the correct logic so the job runs once everyday.

Note: $cache->data below is actually the last time the job ran.

mymodule_cron() {
     $data = '';
     if($cache = cache_get('last-run')) {
         $data = $cache->data;
         if($data <= strtotime('-1 day')) {
               //call helper function to perform some logic
               _some_func();
               $data = time();

               //set update date in cache
               cache_set('last-run', $data, 'cache'));
         }
    }
 }

Answer 1

I don't think there is something wrong on cache_get() and cache_set(). It seems a logic problem. In your code the cache is never set if a cache is not found.

/**
 * Implements hook_cron().
 */
function mymodule_cron() {
  $data = '';

  if ($cache = cache_get('last-run')) {
    $data = $cache->data;
    if($data <= strtotime('-1 day')) {
      //call helper function to perform some logic
      _some_func();
      //set update date in cache
      cache_set('last-run', time(), 'cache'));
    }
  }
  else {
    // set cache if there is no cache.
    cache_set('last-run', time(), 'cache'));
  }
}

Answer 2

I would suggest storing this sensitive data to Drupal variables instead of cache because cache can be wiped by arbitrary code (which probably happens in your case).

Instead of cache_get and cache_set use variable_get and variable_set accordingly.