PS_BLOCKED

[David Xu]

----- Original Message ----- 
From: "Daniel Eischen" <eischen at pcnet1.pcnet.com>
To: "Julian Elischer" <julian at elischer.org>
Cc: "David Xu" <davidxu at freebsd.org>; <freebsd-threads at freebsd.org>
Sent: Monday, April 07, 2003 7:53 PM
Subject: Re: PS_BLOCKED


> On Sun, 6 Apr 2003, Julian Elischer wrote:
> > 
> > On Sun, 6 Apr 2003, Daniel Eischen wrote:
> > 
> > > On Sun, 6 Apr 2003, Julian Elischer wrote:
> > > > 
> > > > If you have this behaviour, please make it an option. Possibly
> > > > One way to do this would be to call kse_create, with the
> > > > 'new-ksegrp' flag set but the mailbox pointer set to NULL.
> > > > 
> > > > However why do you want to use kse_release for this.
> > > > If you have only one thread in the KSEGRP then I'd call this
> > > > "usleep()".
> > > 
> > > It's so that the common code (called by both scope system
> > > threads and scope process threads) can be the same.  I don't
> > > want to have to add checks all over the place to see if the
> > > KSE is bound to a thread or not.  Also, nanosleep doesn't
> > > work well because you can't wake it up with a KSE mailbox
> > > (kse_wakeup), plus there's a race condition if you try and
> > > wake it up before it actually gets to the kernel to sleep.
> > > The kse_wakeup() call is latched, so if it gets to the kernel
> > > first, the next kse_release() will notice it.
> > 
> > you cannot wake up a thread with no upcall mailbox using kse_wakeup
> > because there is no thread mailbox address to match.
> 
> There is a kse mailbox, but no thread mailbox.  I'm trying to
> wakeup a KSE.  What I do for multiple threaded KSEs is:
> 
>   upcall_start(struct kse_mailbox *kse_mbox)
>   {
>     struct kse *curkse = (struct kse *)kse_mbx->km_udata;
> 
>     check_completed(kse);
>     check_waitq(kse);
>     ...
> 
>     while ((td_run = runq_first(kse->k_kseg) == NULL) {
>       get_smallest_thread_wakeup_time(kse, &time_to_sleep);
>       kse->k_waiting = 1;
>       kse_release(&time_to_sleep)
>     }
>     /* switch to thread td_run */
>   }
> 
> Although, for multiple threaded KSEs, the "while" loop
> only executes once because kse_release just causes another
> upcall.  If another KSE makes a thread runnable in the
> first KSEs KSEG's runq, then it wakes up that KSE:
> 
>   _thr_setrunnable(struct kse *curkse, struct pthread *thread)
>   {
>     SCHED_LOCK(curkse);
>     runq_insert(thread->kseg, thread);
>     SCHED_UNLOCK(curkse);
>     if ((thread->kse->k_kseg != curkse->k_kseg) &&
>         (thread->kse->k_waiting != 0)) {
>       thread->kse->k_waiting = 0;
>       kse_wakeup(&thread->kse->k_mbox);
>     }
>   }
> 
> or something like that.
> 
> For a single threaded KSE/KSEG, I don't want the upcall but I
> still want to use kse_release().  I need to be able to wakeup
> that KSE so that it may continue it's thread (it could be the
> thread was in pthread_cond_wait() and it was signalled by
> a thread in another KSE).  And I don't want upcalls on this
> KSE because there is only one thread; I don't want the overhead
> of the upcall and its stack.  And in order to prevent upcalls,
> I have to make sure the kse mailbox has NULL in km_curthread.
> 
> That's the solution I'm looking for.  I think kse_wakeup()
> should be tweakable so that I don't get an upcall.
> 
Yes,  I think kse_release() should be tweaked. however,  because
the thread is no longer an upcalling thread, so how do I deliver
signal ?
I still prefer to deliver signal in legacy mode,  especially for synchronized
signals.

> -- 
> Dan Eischen