User should know if PBSJobManager.updateJobStatus failed

[askask]

When I call one of the queryJobStatus* methods in PBSJobManager, and get back an empty map, I don't know whether no jobs are running anymore, or updateJobStatus/qstat failed.

[dankwart-de]

see PR27 #27
Let's discuss if this is feasible

[vinjana]

The classical way to handle such situation in Java is via exceptions. So better throw an exception with a descriptive message and use appropriate exception classes expressing "qstat failed" and "job not found"!

[vinjana]

• When is the result empty?
• Is there a cache for the job status table?
• Do we need caching with LSF?
• Is the cache ever emptied? How (expiration time? round-robin?)

[vinjana]

Covered by solution #93, to throw an excpetion upon command error.