On 6/5/12 8:11 AM, Felix Meschberger wrote:
Hi,
I fear we are getting on the "ever-and-ever-more-complex" track ...
I understand the concurrency issues (how the come into live) but I would love if we could
solve them with simple code without inventing more and more locking and and signaling
etc. behaviour. This really was the "beauty of some sorts" of the previous
lock-less approach.
I think under certain circumstances there will always be a situation where one
event (service or configuration) is happening while at the same time another
event is being handled. In some situations -- e.g. a required dependency being
unregistered while requiring the component is being activated -- the ongoing
task should probably be aborted and reverted. Which in turn may be simpler
(before service registration) or harder (during service registration).
This can maybe be solved by using checkpoints: Long running tasks (mostly activation)
after each step check the checkpoint while intermittent events (service, configuration)
may set the checkpoint and optionally wait for the checkpoint to be confirmed by the
long-running task (eventually timing out to prevent deadlocks). Such a thing would be
"easier" to implement with an Activating state where just the
Activating.deactivate method might be called which would handle the checkpoint thing.
Do I sound getting complicated ? ;-)
Regards
Felix
It all comes down to a question of guarantees and what you are willing
to live with.
The most basic locking could be accomplished just when touch the
"state". You hold the lock if you are going to change the state.
You use a lock to retrieve the current state. Anything after retrieving
is a best effort. You make the assumption that you exist in this state
until a failure occurs. This would provide guarantees across switching
state and some minimal deadlock prevention.
The ReadWrite lock idea was to just separate the two concepts above.
Transitioning requires the Write lock and the Read lock is used if you
are performing some activity within the given state. It accomplishes
the same goal just with stronger guarantees.
- Michael
