On Fri, Mar 06, 2015 at 02:42:34PM +0100, Michal Privoznik wrote:
> On 06.03.2015 14:31, Peter Krempa wrote:
> > On Thu, Mar 05, 2015 at 12:05:24 +0100, Michal Privoznik wrote:
> >> This patch alone does not make much sense, I know. But it
> >> prepares ground for next patch which when looking up a network in
> >> the object list will not lock each network separately when
> >> accessing its definition. Therefore we must have all the places
> >> changing network definition lock the list.
> >>
> >> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> >> ---
> >> src/conf/network_conf.c | 9 ++++++++-
> >> src/conf/network_conf.h | 3 ++-
> >> src/network/bridge_driver.c | 4 ++--
> >> 3 files changed, 12 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c
> >> index 3d318ce..007cebb 100644
> >> --- a/src/conf/network_conf.c
> >> +++ b/src/conf/network_conf.c
> >> @@ -537,12 +537,19 @@ virNetworkObjSetDefTransient(virNetworkObjPtr network, bool live)
> >> * This *undoes* what virNetworkObjSetDefTransient did.
> >> */
> >> void
> >
> > I've looked through the next patch and you are basically trying to make
> > the name and UUID pointers for domain immutable or at leas write locked
> > ...
> >
> >> -virNetworkObjUnsetDefTransient(virNetworkObjPtr network)
> >> +virNetworkObjUnsetDefTransient(virNetworkObjListPtr nets,
> >> + virNetworkObjPtr network)
> >> {
> >> if (network->newDef) {
> >> + virObjectRef(network);
> >> + virObjectUnlock(network);
> >> + virObjectLock(nets);
> >> + virObjectLock(network);
> >> + virObjectUnref(network);
> >
> > But I don't really like pulling in the complexity into this helper.
> >
> >
> >> virNetworkDefFree(network->def);
> >> network->def = network->newDef;
> >> network->newDef = NULL;
> >> + virObjectUnlock(nets);
> >> }
> >> }
> >
> > While I like the idea, I'd rather see a conversion to R/W locks or
> > making of the name and UUID pointers immutable than this hack.
>
> Well:
>
> 1) We don't have an virObjectRWLockable or something similar. I can add
> it, but that would postpone merging this patchset for yet another version.
>
> 2) Nor UUID nor name can be made immutable, as we are storing just a
> pointers to network objects in the array. Not UUID or name. It's not a
> hash table like in virDomainObjList* [1]. And when looking up an object,
> we access each object's definition directly. Therefore all other places
> changing definition must lock the object list.
This is why I changed the virDomainObjList to use a hash instead of a
list when I introduced lockless access for domain objects.
commit 37abd471656957c76eac687ce2ef94d79c8e2731
Author: Daniel P. Berrange <berrange@xxxxxxxxxx>
Date: Fri Jan 11 13:54:15 2013 +0000
Turn virDomainObjList into an opaque virObject
As a step towards making virDomainObjList thread-safe turn it
into an opaque virObject, preventing any direct access to its
internals.
As part of this a new method virDomainObjListForEach is
introduced to replace all existing usage of virHashForEach
> 1: Yes, one day we can turn the array into hash table too. There's
> plenty of work to be done. I agree. But I prefer it to be divided into
> smaller pieces instead of this one big patchset of hundreds of patches :-P
I'd rather expect to see virNetworkObjList turned into an opaque
struct using a virHashTable internally as the very first patch in
the series. Keeping a list which requires linear scans is incompatible
with doing fast lockless code IMHO
Regards,
Daniel
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