[MAPREDUCE-206] Implement a generic DFA

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Arun Murthy
• Reporter: Arun Murthy
• Created: 20/May/07 19:31
• Updated: 20/Jun/09 07:51

Description

Owen alluded to it HADOOP-1183 and Devaraj talked about this in HADOOP-1337 ... I believe this will be a generally useful feature in other parts of hadoop too...

The proposal is to implement a generic state machine which can be configured as needed and could be used to track states/transitions of various entities. This will hopefully make code less complex (for e.g. in the shuffle) and more maintainable/understandable since the state transitions of entities will be visible in one place (for e.g. where it is configured) and not scattered across myriad sections.

The idea is quite simple:

class StateMachine {

// Register a legal 'transition' from pre to post state on a given event and
// a user-provided hook/callback
void registerTransition(State pre, State post, Event event, Hook hook)
throws IllegalStateTransitionException;

// Effect a transition from the state on the event, return the resulting state or
// throw an exception if the transition is illegal.
// cause/victim are user objects i.e. context/result of the transition.
State doTransition(State state, Event event, Object cause, Object victim)
throws IllegalStateTransitionException;
}

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Thoughts?

Issue Links

• relates to: MAPREDUCE-278 Proposal for redesign/refactoring of the JobTracker and TaskTracker