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Re: [libvirt] [PATCH 0/3] Introduce RW locks to virDomainObjList



On 07/23/2017 07:21 PM, Pavel Hrdina wrote:
> On Sun, Jul 23, 2017 at 02:33:49PM +0200, Michal Privoznik wrote:
>> On 07/23/2017 02:10 PM, John Ferlan wrote:
>>>
>>>
>>> On 07/19/2017 10:31 AM, Michal Privoznik wrote:
>>>> While this is not that critical (hash tables have O(1) time complexity for
>>>> lookups), it lays down path towards making virDomainObj using RW locks instead
>>>> of mutexes. Still, in my limited testing this showed slight improvement.
>>>>
>>>> Michal Privoznik (3):
>>>>   virthread: Introduce virRWLockInitPreferWriter
>>>>   virobject: Introduce virObjectRWLockable
>>>>   virdomainobjlist: Use virObjectRWLockable
>>>>
>>>>  src/conf/virdomainobjlist.c |  24 ++++----
>>>>  src/libvirt_private.syms    |   4 ++
>>>>  src/util/virobject.c        | 144 ++++++++++++++++++++++++++++++++++----------
>>>>  src/util/virobject.h        |  16 +++++
>>>>  src/util/virthread.c        |  35 +++++++++++
>>>>  src/util/virthread.h        |   1 +
>>>>  6 files changed, 180 insertions(+), 44 deletions(-)
>>>>
>>>
>>> This could be a "next step" in the work I've been doing towards a common
>>> object:
>>
>> Sure. If we have just one common object the change can be done in one
>> place instead of many. I don't care in what order are the changes merged.
> 
> I'm still not sure about the implementation that you are heading to,

"you" as in John or as in me?

> I would actually prefer something similar to the current
> virDomainObjList implementation, create a new module in utils called
> virObjectList and make it somehow generic that it could be used by our
> objects.  I personally don't like the fact that there will be two new
> classes, one that enables using the other one.

Well I think we need two classes. A list of objects is something
different than objects themselves. You can hardly assign some meaning to
virDomainObj.lookupByName() or virDomainObjList.startCPUs(). It's
important to differentiate "data an object is working with" and
"operations an object can do". The fact that virDomainObjList works with
virDomainObj doesn't mean it should be in any sense derived. In OOP, if
class B is derived from class A, it means that B has all the
attributes/methods that A has, plus something more, e.g. because B is
more specialized. For instance, assume we have virCarClass. Then,
virTruckClass or virV8TurboCharged3LClass can both be derived from
virCarClass. But I can hardly imagine virParkingLotClass doing the same
thing.

Michal


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