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https://issues.apache.org/jira/browse/YARN-117?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13631364#comment-13631364
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Steve Loughran commented on YARN-117:
-------------------------------------

updated patch where {{TestNodeStatusUpdater.testNMConnectionToRM()}} should not 
fail irrespective of how long it takes for the NM's {{init()}} process to take. 
Until now the custom {{NodeStatusUpdater}}  set its clock in the constructor, 
which was called during the NM's {{init()}}, but the test only set it's clock 
after {{init()}} and before {{start()}}. As a result, if the init took too 
long, the test would fail saying "the RM took too long", when the delay logic 
was actually working.

The fix is for the custom {{NodeStatusUpdater}} to set its {{waitStartTime}} in 
it's {{innerStart()}}, so only when the service is started. This has a narrower 
gap between the tests's measured start time and the updater -though the time to 
start a couple of services before the updater is started could still be 
troublesome.

Even so, retaining the time measurement logic in the test (rather than just 
probing the Updater to verify it triggered) is essential to be confident that 
{{NodeManager().start()}} doesn't complete until the connection has been 
established
                
> Enhance YARN service model
> --------------------------
>
>                 Key: YARN-117
>                 URL: https://issues.apache.org/jira/browse/YARN-117
>             Project: Hadoop YARN
>          Issue Type: Improvement
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: YARN-117-2.patch, YARN-117-3.patch, YARN-117.4.patch, 
> YARN-117.5.patch, YARN-117.patch
>
>
> Having played the YARN service model, there are some issues
> that I've identified based on past work and initial use.
> This JIRA issue is an overall one to cover the issues, with solutions pushed 
> out to separate JIRAs.
> h2. state model prevents stopped state being entered if you could not 
> successfully start the service.
> In the current lifecycle you cannot stop a service unless it was successfully 
> started, but
> * {{init()}} may acquire resources that need to be explicitly released
> * if the {{start()}} operation fails partway through, the {{stop()}} 
> operation may be needed to release resources.
> *Fix:* make {{stop()}} a valid state transition from all states and require 
> the implementations to be able to stop safely without requiring all fields to 
> be non null.
> Before anyone points out that the {{stop()}} operations assume that all 
> fields are valid; and if called before a {{start()}} they will NPE; 
> MAPREDUCE-3431 shows that this problem arises today, MAPREDUCE-3502 is a fix 
> for this. It is independent of the rest of the issues in this doc but it will 
> aid making {{stop()}} execute from all states other than "stopped".
> MAPREDUCE-3502 is too big a patch and needs to be broken down for easier 
> review and take up; this can be done with issues linked to this one.
> h2. AbstractService doesn't prevent duplicate state change requests.
> The {{ensureState()}} checks to verify whether or not a state transition is 
> allowed from the current state are performed in the base {{AbstractService}} 
> class -yet subclasses tend to call this *after* their own {{init()}}, 
> {{start()}} & {{stop()}} operations. This means that these operations can be 
> performed out of order, and even if the outcome of the call is an exception, 
> all actions performed by the subclasses will have taken place. MAPREDUCE-3877 
> demonstrates this.
> This is a tricky one to address. In HADOOP-3128 I used a base class instead 
> of an interface and made the {{init()}}, {{start()}} & {{stop()}} methods 
> {{final}}. These methods would do the checks, and then invoke protected inner 
> methods, {{innerStart()}}, {{innerStop()}}, etc. It should be possible to 
> retrofit the same behaviour to everything that extends {{AbstractService}} 
> -something that must be done before the class is considered stable (because 
> once the lifecycle methods are declared final, all subclasses that are out of 
> the source tree will need fixing by the respective developers.
> h2. AbstractService state change doesn't defend against race conditions.
> There's no concurrency locks on the state transitions. Whatever fix for wrong 
> state calls is added should correct this to prevent re-entrancy, such as 
> {{stop()}} being called from two threads.
> h2.  Static methods to choreograph of lifecycle operations
> Helper methods to move things through lifecycles. init->start is common, 
> stop-if-service!=null another. Some static methods can execute these, and 
> even call {{stop()}} if {{init()}} raises an exception. These could go into a 
> class {{ServiceOps}} in the same package. These can be used by those services 
> that wrap other services, and help manage more robust shutdowns.
> h2. state transition failures are something that registered service listeners 
> may wish to be informed of.
> When a state transition fails a {{RuntimeException}} can be thrown -and the 
> service listeners are not informed as the notification point isn't reached. 
> They may wish to know this, especially for management and diagnostics.
> *Fix:* extend {{ServiceStateChangeListener}} with a callback such as 
> {{stateChangeFailed(Service service,Service.State targeted-state, 
> RuntimeException e)}} that is invoked from the (final) state change methods 
> in the {{AbstractService}} class (once they delegate to their inner 
> {{innerStart()}}, {{innerStop()}} methods; make a no-op on the existing 
> implementations of the interface.
> h2. Service listener failures not handled
> Is this an error an error or not? Log and ignore may not be what is desired.
> *Proposed:* during {{stop()}} any exception by a listener is caught and 
> discarded, to increase the likelihood of a better shutdown, but do not add 
> try-catch clauses to the other state changes.
> h2. Support static listeners for all AbstractServices
> Add support to {{AbstractService}} that allow callers to register listeners 
> for all instances. The existing listener interface could be used. This allows 
> management tools to hook into the events.
> The static listeners would be invoked for all state changes except creation 
> (base class shouldn't be handing out references to itself at this point).
> These static events could all be async, pushed through a shared 
> {{ConcurrentLinkedQueue}}; failures logged at warn and the rest of the 
> listeners invoked.
> h2. Add some example listeners for management/diagnostics
> * event to commons log for humans.
> * events for machines hooked up to the JSON logger.
> * for testing: something that be told to fail.
> h2.  Services should support signal interruptibility
> The services would benefit from a way of shutting them down on a kill signal; 
> this can be done via a runtime hook. It should not be automatic though, as 
> composite services will get into a very complex state during shutdown. Better 
> to provide a hook that lets you register/unregister services to terminate, 
> and have the relevant {{main()}} entry points tell their root services to 
> register themselves.

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