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https://issues.apache.org/jira/browse/HADOOP-13035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15266325#comment-15266325
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Steve Loughran commented on HADOOP-13035:
-----------------------------------------
Thinking about this more, it is possible to make the fact that a service is in
a transition state without changing {{Service.STATE}}, which is the
incompatibility barrier.
What is needed is to retain that state model to all existing code, while either
making the state-transition-in-progress condition visible to code
which is aware of the fact that the intermediate states are visible.
This can be done in a number of ways
h3. a {{transitionInProgress}} variable and accessor
When state is entered, the (atomicBoolean) state is set, cleared on exit. The
state of a service can be queried with something like
{{isInState(STATE.STARTED) && !transitionInProgress}}.
Troubespots here are that such a probe is not in itself atomic except if
executed in a {{synchronized block}}, which will also be needed when entering
the state. The extra fun happens when stop() is called during a change, or, say
{{start() in init()}}. There are some other corners too: what if the flag is
set, but the service is in state {{NOTINITED}}?
h3. Implement the extended state as a new enum, translate down to the existing
state for existing code in the getters and state probes.
Here there'd be a new interface
{code}
interface ExtendedService extends Service {
enum ExtendedState{ ... = Service.state + transitions}
boolean getExtendedState();
boolean isInExtendedState(ExtendedState es);
boolean canEnterExtendedState(ExtendedState es)
}
{code}
The state model would be the extended one, what would change is the old state
queries
{code}
boolean isInState(Service.State s) {
ExtendedState es = getExtendedState();
return mapExtendedToSimpleState(es) == s
}
public State mapExtendedToSimpleState(ExtendedState es) {
switch(es) {
case NOTINITED: return State.NOTINITED;
case INITED: return State.INITED;
case INITING: return State.INITED;
...
}
}
{code}
Actually, you could do the map in the enum itself, with every ExtendedState
instance declaring is simple state in the constructor.
I *believe* this could work, the troublespot would be managing state entry
calls, including {{enterState(State.STARTED)}}, and the addition of child
services within a composite service during the {{serviceInit()}} and
{{serviceStart()}} operations.
If this can be shown to implement the extended state model desired and retain
backwards compatibility with subclasses of {{AbstractService}} inside and
outside the Hadoop codebase then I'm prepared to withdraw my -1. I do still
require the linked JIRAs to go in first, as they push the boundaries of the
state model further, and, being derivative of the slider workflow services and
service launcher, something we could migrate that code to. That is: if the
YARN-679 and YARN-1564 handle this, then testing slider becomes a lot easier.
> Add states INITING and STARTING to YARN Service model to cover in-transition
> states.
> ------------------------------------------------------------------------------------
>
> Key: HADOOP-13035
> URL: https://issues.apache.org/jira/browse/HADOOP-13035
> Project: Hadoop Common
> Issue Type: Bug
> Reporter: Bibin A Chundatt
> Attachments: 0001-HADOOP-13035.patch, 0002-HADOOP-13035.patch,
> 0003-HADOOP-13035.patch
>
>
> As per the discussion in YARN-3971 the we should be setting the service state
> to STARTED only after serviceStart()
> Currently {{AbstractService#start()}} is set
> {noformat}
> if (stateModel.enterState(STATE.STARTED) != STATE.STARTED) {
> try {
> startTime = System.currentTimeMillis();
> serviceStart();
> ..
> }
> {noformat}
> enterState sets the service state to proposed state. So in
> {{service.getServiceState}} in {{serviceStart()}} will return STARTED .
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