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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1395) Implement a generic DFA
Date Sun, 20 May 2007 19:33:17 GMT
Implement a generic DFA 

                 Key: HADOOP-1395
                 URL: https://issues.apache.org/jira/browse/HADOOP-1395
             Project: Hadoop
          Issue Type: New Feature
            Reporter: Arun C Murthy
         Assigned To: Arun C Murthy
             Fix For: 0.14.0

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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