(PECL gearman >= 0.5.0)
GearmanClient::addTaskLowBackground — Add a low priority background task to be run in parallel
$function_name
   , string $workload
   [, mixed &$context
   [, string $unique
  ]] )Adds a low priority background task to be run in parallel with other tasks. Call this method for all the tasks to be run in parallel, then call GearmanClient::runTasks() to perform the work. Tasks with a low priority will be selected from the queue after those of normal or high priority.
function_name
     由程序自动执行的已注册函数。
workload
     被处理的序列化数据
context
     与任务关联的应用程序上下文
unique
     用于标识特定任务的唯一 性ID。
   A GearmanTask object or FALSE if the task could not be added.