Re: callout(9) and Giant lock

>
> On Sun, 28 Jun 2009, Sebastian Huber wrote:
>
> > suppose that a certain time event triggered several callout functions. What
> > happens if the first of these callout functions blocks on the Giant lock?
> > Does this delay all further callout functions until the Giant lock is
> > available for the first callout function? What happens if one of the callout
> > function blocks forever? Does this deadlock the system?
>
> Callouts are marked as MPSAFE or non-MPSAFE when registered.  If non-MPSAFE,
> we will acquire Giant automatically for the callout, but I believe we'll also
> try and sort non-MPSAFE callouts behind MPSAFE ones in execution order to
> minimize latency for MPSAFE callouts.  Most callouts acquire locks of some
> sort, and stalling any callout indefinitely will stall the entire callout
> thread indefinitely, which in turn could lead to a variety of odd behaviors
> and potentially (although not necessarily) deadlock.