Re: [PATCH] Per-task watchers: Enable inheritance

[jtk@us.ibm.com (John T. Kohl)]

>>>>> "Matt" ==   <matthltc@us.ibm.com> writes:

Matt> On Fri, 2006-06-23 at 17:17 -0400, John T. Kohl wrote:
>> >>>>> "MattH" ==   <matthltc@us.ibm.com> writes:
>> 
MattH> This allows per-task watchers to implement inheritance of the
MattH> same function and/or data in response to the initialization of
MattH> new tasks. A watcher might implement inheritance using the
MattH> following notifier_call snippet:
>> 
>> I think this would meet our needs--we (MVFS) need to initialize some new
>> state in a child process based on our state in the parent process
>> (essentially, module-private inherited per-process state).  It may still
>> be a bit clumsy to find the per-process state in other situations,
>> though.  While a process is executing our module's code, would it be
>> safe to traverse current's notifier chain to find our state?

Matt> 	Hmm. We may need to be careful with terminology here. Keep in mind that
Matt> a task is not the same as the userspace concept of a  "process".

Right, sorry, I was imprecise in my wording.  What MVFS wants is per-task
private state and state inheritance on task forks.

Matt> 	When a task is executing a module's code it will be safe to traverse
Matt> the task's notifier chain to find state. It will *not* be safe to
Matt> traverse the notifier chain of other tasks -- even if the other task is
Matt> a thread in the same "process".

I'm curious to see Peter's prototype code (mentioned in his reply).  I
worry that to get safe access to the parent task's private state during
fork, we'll need something like a private hash table for our private
per-task state.  Ideally we'd like to just be able to find stuff hanging
off the task structure directly.

-- 
John Kohl
Senior Software Engineer - Rational Software - IBM Software Group
Lexington, Massachusetts, USA
jtk@us.ibm.com
<http://www.ibm.com/software/rational/>