[TYPO3-core] RFC #12068: Bug: Scheduler: Improper skipping of running tasks in case multiple execution denied

[Francois Suter]

This is an SVN patch request.

Type: Bugfix

Bugtracker references:
http://bugs.typo3.org/view.php?id=12068

Branches:
Trunk

Problem:
The Scheduler has a mechanism for preventing multiple concurrent 
executions of the same task. This is logged into the sys_log table. If a 
CLI call is running and a new one starts while the previous run is not 
finished (which happens e.g. with a cron job because it will fork its 
process if the previous one is not finished), the Scheduler runs into an 
endless loop and floods the sys_log table.

Solution:
The next execution time of task must be calculated when the task is 
launched and not after it has finished. It must also be calculated when 
a task is skipped, in order to postpone it to the next execution time in 
the schedule. This prevents the endless loop.

Notes:
Changing the position of the save() call (which calculates the next 
execution date) has a slight impact on success/failure reporting. Indeed 
tx_scheduler::executeTask() used to return the status of the save() call 
when a task had been executed. This was wrong anyway as a failure was 
reported as an execution failure, whereas it could have been a DB update 
failure. After this patch the Scheduler will report correctly as to the 
execution, but there's no reporting in case of DB update failure. This 
should be corrected, but in a separate RFC (it is not trivial given the 
current process).

Cheers

-- 

Francois Suter
Cobweb Development Sarl - http://www.cobweb.ch

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