Re: workqueue semantics [was Re: How to identify specific wait-state for a "DE" process?]

[Paul Goyette <paul%whooppee.com@localhost>]

On Tue, 5 Jan 2016, Thor Lancelot Simon wrote:

> On Wed, Jan 06, 2016 at 11:38:00AM +0800, Paul Goyette wrote:
> > On Wed, 6 Jan 2016, Taylor R Campbell wrote:
> >
> > >  Date: Tue, 5 Jan 2016 21:48:42 -0500
> > >  From: Thor Lancelot Simon <tls%panix.com@localhost>
> > >
> > >  You can probably use workqueues for this.  Looking at the manual page
> > >  again for the first time in years, I think it's a little misleading --
> > >  what I believe is meant by "A work must not be enqueued again until the
> > >  callback is called..." is really "a work item must not be re-enqueued
> > >  before it has been processed by the *func callback", not the alternate,
> > >  crazy reading that would imply workqueues can only have one enqueued
> > >  item at a time.
> > >
> > > Your reading of the man page is correct: it is the struct work, not
> > > the struct workqueue *, that may not be reused until the callback is
> > > run.
> > >
> > > (I'm not sure how this would help for pgoyette's application, though.)
> >
> > I don't know how it would help, either.  The best I can think of is to have
> > a periodic task run which checks to see if the file descriptor is being
> > closed;  if yes, then the code could release the reference and wake up the
> > condvar waiter.  But is this really a good thing to do?  And what would be
> > an appropriate interval?
>
> Why do you need a periodic task?  When you enqueue the work to release the
> reference, the workqueue framework will run the callback function -- in a
> different thread.  Then it can wake you up.  Isn't that what you wanted?

The problem is, what triggers "enqueue to the work queue"?  It needs to 
happen only _after_ entry to sys_exit(), but _before_ the exit code gets 
around to calling fd_free() which sequentially calls fd_close(fd) ...

I don't want to release the reference while things are running, only 
when they're done.

Something like an atexit(3) for the kernel!   :)



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