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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10085) CompositeService should allow adding services while being inited
Date Wed, 13 Nov 2013 15:49:23 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13821442#comment-13821442
] 

Steve Loughran commented on HADOOP-10085:
-----------------------------------------

I've been through all the hadoop-trunk code & looked at when {{addService()} is called.
Mostly its called in {{serviceInit()}} before a call to {{super.serviceInit()}} -adding UNINITED
services which get inited during the loop through the children. {{ResourceManager}} is the
busiest class here.

{{ContainerManagerImpl }}adds a service in its constructor which is mildly hazardous as if
that method were overridden in a test subclass then the subclass would be in use before it
had fully constructed. That doesn't impact service states though.

now, some fun arises in calling {{addService()}} in your {{serviceInit()}} operation, because
although the run through to init the child services hasn't started yet (i.e. the operations
to move the children from UNINITED -> INITED, the parent is already in the INITED state.
A check to validate that you can add an UNINITED service fails, because the parent is actually
mid-init.

There's no easy solution here, so I propose
# don't implement any checks on service state when adding a child.
# if you do a state transition that isn't legal, you'll find out at the time.
# we make the new tests verify today's operation: you can insert children in any state, but
when the parent tries to enter any state other than stopped, if there is a mismatch in versions
a {{ServiceStateException}} gets thrown.



> CompositeService should allow adding services while being inited
> ----------------------------------------------------------------
>
>                 Key: HADOOP-10085
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10085
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 2.2.0
>            Reporter: Karthik Kambatla
>            Assignee: Steve Loughran
>         Attachments: HADOOP-10085-002.patch
>
>
> We can add services to a CompositeService. However, if we do that while initing the CompositeService,
it leads to a ConcurrentModificationException.
> It would be nice to allow adding services even during the init of CompositeService.



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