Retries

Issue Summary

I want to integrate the module Views Send with Job queue in order to abstract the way messages are spooled for sending but there is an important feature missed in Job queues: Retries.

After an item is processed, is deleted from the queue even the function failed to do the job. For example if the $function = 'drupal_mail', Job queue should check if the function was executed with success first. If yes, remove from the queue, if no just requeue the item for a later retry.

In my module I used a separate DB field: "tentatives" (could be "attempts") which defaults to 0 when the item is queued. On each failure this field increase by one. On the next cron, records with higher number of tentatives are placed at the bottom of query result. They have lower priority. Administrators can configure a maximum number of tentatives so that queue items reaching this number are purged too.

On an e-mail job queue this seems to be something mandatory.