[Pvfs2-developers] job interface

[Phil Carns]

Hi Walt,

I have been away from email since Wednesday of last week so I am just 
now catching up- but I may as well jump in on this question.

Would the job_null() function do what you want?  It never immediately 
completes, and doesn't actually do any work.  It is just a way to 
trigger a transition in a state machine (which may be a different state 
machine from the one that actually called job_null()- you just have to 
set the user_ptr appropriately).  This was something I added a while 
back as a mechanism to trigger transitions across cobbled together 
parallel machines.

The only difference from what you describe is that there is no release 
phase- just a post.  You could possibly use it to trigger a transition 
to a state that has a counter in it though (if count < n, transition to 
myself, otherwise go to next state) in order to add an arbitrary number 
of conditions that need to be triggered before the "real" transition.

If you really need the post/release model (and don't want to add 
complexity to the states), then you might still want to look at job_null 
as a starting point- just split it into two functions.  The post would 
just allocate a job descriptor and set some counter in it of how many 
releases are needed before it completes.  The second function would be a 
release function that decrements the counter and then moves it to the 
completion queue when it hits zero.

If you do the above approach, you just need to update the one occurence 
of job_null() in the current cvs tree to do a post immediately followed 
by a release.  Or maybe if the post function takes an argument to tell 
it how many releases are needed and you can just pass in 0 to get the 
old behavior.

At any rate, I think the functionality that you need can all be done at 
the job level without adding much code.

-Phil

Walter B. Ligon III wrote:
> 
> I need a crash course in the job interface.
> 
> I need to add something a lot like the scheduler but without any 
> intelligence.  Basically I'd like a SM to be able to post a job which 
> will never have immediate completion.  Then later another SM posts a 
> release that lets the first job go.  It looks like the stuff that 
> already exists for the scheduler is pretty close to what I want, except 
> I don't want any of the scheduler bits.  What isn't clear to me is how a 
> job moves to the completed list, or how I can maintain a list of waiting 
> jobs and look those up.  It appears some of that is going on in the 
> calls in job.c but I don't know what's being done by the job layer and 
> what is being done by the scheduler.
> 
> If someone who knows this stuff can email me so I can get a few 
> questions answered then I can forge ahead myself.
> 
> Thanks!
> 
> Walt