Cron Jobs, Task Queue or Deferred Tasks?

In Google App Engine, for a task like scanning some RSS feeds and adding new entries from the feed to the datastore every 10-15 seconds, should I use Cron开发者_JAVA百科 Jobs, Task Queue or Deferred Tasks? I'm really confused.

Invoke a cron job every 1 minute, which would get the RSS and sleep for 15 seconds four times. You can locks to prevent overlapping (although the database insertion provides some measure of concurrency control).

Python-like pseudo code:

if cant_get_lock:
    exit
else:
for i in (1,2,3,4):
    get RSS
    sleep 15 seconds

• I think if it happens every 15 seconds(not skipping) than I would cron jobs because that is easiest to implement. But if you need to be able cancel task then you should use task queue.
• BTW you should use PubSubHubbub(hubbub) to receive updates for the feeds in realtime if I understand you correctly.