+ * altering task priority

+ The **channel** policy is used to determine the channel for a task. It supports

+ The **priority** policy is used to alter task's priority. In most cases you

+ should manage priorities by different channels and builders assigned to them.

+ There is nevertheless few corner-cases which can benefit from altering task's

+ priority.

+ 

+ Note, that you can easily get to deadlock situation if this is not handled with

+ caution (lower priority tasks will get assigned only if there is no higher

+ priority task for given channel).

+ 

+ .. note::

+     For example OSBS use this mechanism to propagate higher priority tasks to

+     its plugin.  Deadlock problem is here mitigated by limiting policy to

+     ``buildContainer`` tasks only. These tasks are consumed only by dedicated

+     builders/channel, so they will not take priority over other types of tasks

+     (e.g. ``newRepo`` or ``tagBuild`` tasks which could be blocked otherwise.

+ 

+ Technically it is very similar to **channel** policy. Only actions are

+ different:

+ 

+ ``stay``

+     * don't touch the default priority of the task

+ 

+ ``set <int>``

+     * set priority to this value

+ 

+ ``adjust +<int>``

+     * increment default priority

+ 

+ ``adjust -<int>``

+     * decrement default priority

+ 

+     ruleset = context.policy.get('priority')

+     result = ruleset.apply(policy_data)

+     if result is None:

+         logger.warning('Priority policy returned no result, using default value: %s'

+                        % opts['priority'])

+     else:

+         try:

+             parts = result.split()

+             if parts[0] == 'stay':

+                 # dont' change priority

+                 pass

+             elif parts[0] == 'set':

+                 # fixed value

+                 opts['priority'] = int(parts[1])

+             elif parts[0] == 'adjust':

+                 # note: int() will accept our preferred "+1" representation for increments

+                 opts['priority'] += int(parts[1])

+             else:

+                 logger.error("Invalid result from priority policy: %s", ruleset.last_rule())

+                 raise koji.GenericError("invalid priority policy")

+         except (IndexError, ValueError):

+             logger.error("Invalid result from priority policy: %s", ruleset.last_rule())

+             raise koji.GenericError("invalid priority policy")

+ 

+     'priority': '''

+             all :: stay

+             ''',