On 06.03.2015 15:15, Daniel P. Berrange wrote:
> 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
Yes, this could work. Although, I'm inclined to push patches from
beginning till 09/24 and introduce patch turning the array into a hash
table right after that. My rationale is that at point of 09/24 whole
code uses accessors to the network object list so turning array into
hash table could end up being small patch. Objections?
Michal
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