Description:
------------
When the value is already initialized in the apcu cache, apcu is hanging/freezing in an unpredictable manner. It often happens on the first request after not hitting the script for a few minutes, or sometimes after hitting the script repeatedly.

Test script:
---------------
function loadCSV($file_path) {
  $rows = array_map('str_getcsv', file($file_path));
  $header = array_shift($rows);
  $csv = array();
  foreach($rows as $row) {
    $csv[] = array_combine($header, $row);
  }
  return $csv;
}

$degrees = apcu_entry('degreeList.csv', 'loadCSV');
echo json_encode($degrees);


Expected result:
----------------
apcu_entry should never hang, freeze, or deadlock.

Actual result:
--------------
apcu_entry freezes under low load testing conditions.