[libvirt] libvirt(-java): How to make vm.getDomain().getJobInfo() thread safe?

[Thomas Treutner]

Hi,

this is kind of a follow-up to an older question/discussion:
https://www.redhat.com/archives/libvir-list/2010-July/msg00267.html

As a result of that, I use a second thread for monitoring the live 
migration, taking actions (setting maxdowntime to a value that fits the 
situation) if necessary.

Although I call getJobInfo() with a quite low frequency (once a second), 
problems are occuring frequently, like every 10th or 15th live 
migration. Problems range from exceptions that the domain is not running 
anymore to complete JVM crashes -> http://pastebin.com/jT6sXubu
Recovery from exceptions doesn't seem to work perfectly, as they seem to 
trigger that connections to a host can't be shut down properly because 
there are still open references.

Of course, in my monitoring thread I'm checking in every monitoring 
iteration if the domain object is not null, is still active, if the 
jobInfo is available yet etc. But, as I can not synchronize with 
vm.migrate(), there still a reasonable chance that migrate() just 
invalidates the current domain while I'm accessing it, no matter what I do.

Do I miss something or is that correct? Any ideas how to reliably solve 
it? Is there some experience from virt-manager, where (in my quite old 
version) I assume at least the domain is read for cpu etc. stats while 
live migrating...


regards,
thomas