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From Greg Trasuk <tras...@stratuscom.com>
Subject Re: TaskManager requirements
Date Tue, 13 Jul 2010 13:04:51 GMT

On Tue, 2010-07-13 at 07:28, Peter Firmstone wrote:
> Ok, understood, ANY throwable sounds bad, we should probably pick 
> something sensible in the Error / Exception hierarchy, that it and below 
> will log the exception, and anything else above isn't caught, but left 
> to bubble up the call stack.
> 

Except that when a Throwable pops out of a Task's run method, the call
stack is not relevant.  The original thread associated with the task is
off doing something else.  Is it worth having a notification mechanism
so that the TaskManager can notify the Tasks's originator?  I'd say if
the Task author cares that much about being notified of a Throwable,
he/she can write that functionality into the Task.

What would you propose to do in case of a "catastrophic" Throwable? 
System.exit()?  Is that up to TaskManager to decide? Again, I'd say if
the task author has some reasonable action in mind, let them catch the
Throwable and take their action.

I wouldn't spend too much time pondering any such additions to
TaskManager.  It's quite common to just catch a Throwable in case of
NullPointerExceptions.  If something more disastrous comes along,
there's probably not much you can do about it anyway.

Cheers,

Greg.

> Patricia Shanahan wrote:
> > On 7/13/2010 1:10 AM, Peter Firmstone wrote:
> >> Patricia Shanahan wrote:
> >>> I'm getting into writing a new TaskManager, and have a requirements
> >>> question. I expect I will have more of them as time goes on.
> >>>
> >>> TaskManager logs and ignores any Throwable from a Task's run method.
> >>>
> >>> This troubles me for a couple of reasons. Given the rule that an
> >>> interrupt is issued to each Thread during TaskManager termination, I
> >>> do not think InterruptedException should be loggable. On the other
> >>> hand, should we really be going on running, with just a Level.WARNING
> >>> log message, after a really bad JVM problem?
> >>>
> >>> Patricia
> >>>
> >> I was thinking about that recently and thought that it should be
> >> possible to ask a task it's status. If it has encountered an error, or
> >> exception, that could be retrieved, similar to a RunnableFuture. Like
> >> you have mentioned, not all exceptions should be caught. Have a look at
> >> the comments in JoinManager, there's some interesting comments in there
> >> that you might find relevant. If interrupted, it's possible it will be
> >> run again.
> >
> > The Task is a Runnable, and has a Runnable's inherent power to wrap the
> > body of its run method in a try-catch. The problem I'm concerned about
> > is the handling of disastrous Throwables, such as VirtualMachineError.
> > Those are not normally caught, so I would not expect the Task to catch 
> > them. A warning log message seems an under-reaction.
> >
> > I've realized we will never get InterruptedException from calling the
> > run method, because it is not an Error or a RuntimeException.
> >
> > Patricia
> >
-- 
Greg Trasuk, President
StratusCom Manufacturing Systems Inc. - We use information technology to
solve business problems on your plant floor.
http://stratuscom.com


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