[Buildbot-devel] Why slaves locked by a builder lock are considered as available by this builder

[Alberdi, IonX]

Hello,
I have a question regarding locks on slaves.
Indeed I'm very interesting on the feature that
enables one user to limit the number of // builds a slaves does thanks
To the SlaveLock objects. However, this feature does not exactly work as I expected.
Let us say we have two slaves, sl1, sl2, and three builders b1,b2,b3, configured like that:

slave_lock = SlaveLock("slavelock",
                       maxCountForSlave = { sl1: 2,sl2:1 })
...
Def nextSlave(builder,slavebuilders):
... if sl1 in slavebuilders:
               Return sl1
   Else:
            Return sl2

for b in b1,b2,b3:
BuilderConfig(name=b,
                          slavenames=[sl1,sl2],
                           nextSlave = nextSlave,
                           locks = [slave_lock])

Let us say we launch b1,b2 and b3 in //. In this case, the three builds will be created, and choose
sl1. However, even if created, one of the builds will be in "waiting for lock" state.
This is sad because sl2 is available and could be used to run the locked build.
My questions are therefore the followings:
. Is there a reason why the slaves locked by the builder lock are put in the available_slavebuilders list ?
(master/buildbot/process/builder.py)
available_slavebuilders = [ sb for sb in self.slaves
                                    if sb.isAvailable() ]
Indeed, the sb.isAvailable() checks that the slave is not to be locked by one of its own locks. Therefore, I wonder
Whether we could do something like:
available_slavebuilders = [ sb for sb in self.slaves
                                                 if sb.isAvailable() and self.OwnLocksdoNotLock(sb) ]

self.OwnLocksDoNoLock checking that any of the locks of the builder do not hold one slave.

. If a reason not to implement this modification exists, could you give me your advice on
the best way to implement the fact that a locked slave (by the builder lock)
Is not chosen and affected to the next build to create ?
More precisely, should I check that from:
- a nextSlave function, or
- use locks that can be set up in the BuildSlave constructor ? (from what I understood, these are the locks that are actually checked In sb.isAvailable())

Thanks in advance

--
Ion

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