[Maas-devel] Race in Node.acquire()?

[Jeroen Vermeulen]

On 05/01/2014 02:37 AM, Julian Edwards wrote:

>> And what would we be waiting for?  If the node is locked, it's probably
>> because someone else is already allocating it.
> 
> Not necessarily, and if that is the case then when the locked thread is
> freed it won't see the allocated node due to the query filtering.

Looks like we have different ways of doing this in mind.  You seem to be
thinking of doing a select-for-update query to find the first available
match, and either block or retry if the query gives you a locked node.

I was thinking to do the filtering just once without lock, and then walk
through the result to find a candidate that we can lock, and once we do,
we check if it's still available.

That way, there's no waiting at all for locked nodes.  If another client
holds a lock on one of the candidates, we just move on to the next.


Jeroen