Yarn service subclasses don't check for service state before executing their
state change operations
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Key: MAPREDUCE-3535
URL: https://issues.apache.org/jira/browse/MAPREDUCE-3535
Project: Hadoop Map/Reduce
Issue Type: Bug
Components: mrv2
Affects Versions: 0.23.0, 0.24.0
Reporter: Steve Loughran
Although there are checks in the lifecycle state change methods (start, stop,
...), they only get checked in the superclass. The subclasses don't check it;
they don't exit the start() method if they are already started, and they don't
bail out early on a stop if they are already stopped -even when the superclass
returns without doing anything.
This means that calling {{Service.start()}} twice may leak resources,
{{Service.start()}} twice try to shut down twice, etc. And that's on the same
thread...
My preferred action here would be for the ave the operations return true if a
state change took place, the implementation would be synchronised and return
the correct value
The subclasses look for this and only execute their state changes took place
e.g
{code}
boolean start() {
if (!super.start()) return false;
//do my own startup
return true;
}
{code}
The {{Service.stop()}} operation is trickier as the subclasses tend to call the
superclass last for a better unwinding. I think it may be safer to work the
other way around, but code reviews would be need to ensure that this doesn't
break assumptions in the subclass about termination order. It may be possible
to do more complex designs, but it is hard to chain this down a hierarchy of
classes.
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