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

[Michal Privoznik]

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.

> 
> https://www.redhat.com/archives/libvir-list/2017-June/msg00916.html
> 
> which moves all those driver/vir*obj list API's for Lookup, Search,
> ForEach, Add, Remove, etc. into object code since they're essentially
> all following the same pattern.
> 
> Once there - altering the Lockable lock under the covers should be
> relatively simple. I would be called a ListLock or HashLock instead of
> an RWLock and the implementation is such that it's R or W depending on
> API. Taking a quick refresher look at the series, for a new object I
> call virObjectLookupHashClass - that could be the integration point to
> use a local initialization for the class and then the appropriate lock
> style depending on API.

I think I still prefer "RWLock" name over "ListLock" or "HashLock" since
its name clearly suggests its purpose. I mean, ListLock doesn't say it's
an RW lock. Moreover, as I say in the cover letter, I'd like to use RW
locks for virDomainObj one day (for instance, there's no reason why two
clients cannot fetch XML for the same domain at the same time).
Therefore, it looks correct to me to derive virDomainObjClass from
virObjectRWLockable instead of ListLock or HashLock or something.

> 
> Just thinking off the cuff and of course trying to keep stuff I've been
> working on fresh ;-)

Sure, the more recent some patches are the more I understand them. Same
here :-)

Michal