Re: [libvirt-users] Is this Race Condition?

On Thu, Apr 05, 2012 at 06:06:43PM +0800, Zhihua Che wrote: > Hi, everyone > >     I'm  writing application using libvirt and I need call > virDomainGetCPUStats to get domain cpu stats . I learn from API > reference that this function has to be called when domain is running. > So my question is if there is an atomic way to test the domain's state > and get its stats? > >    Or, it's ok to call this function when domain is not active, but > caller just gets error returned. > >    In my code, I just call it directly and return error. I wonder if > this programming practice has subtle problem like race condition. For a function which is only callable when the domain is running, libvirt will return a special error code  VIR_ERR_OPERATION_INVALID  if you invoke it when the domain is shutoff. Thus the race-free way to deal with this scenario is to just call the API, and check for VIR_ERR_OPERATION_INVALID. Any other error code is an indication of a "real" error situaton. Regards, Daniel --