On Dec 21, 2007 10:41 AM, Igor Stasenko <siguctua at gmail.com> wrote:

> On 20/12/2007, Michael van der Gulik <mikevdg at gmail.com> wrote:
> >
> >
> > On Dec 21, 2007 8:09 AM, Igor Stasenko <siguctua at gmail.com> wrote:
> > >
> > > On 20/12/2007, Tom Phoenix <rootbeer at redcat.com> wrote:
> > > > On 12/20/07, Igor Stasenko <siguctua at gmail.com> wrote:
> > > >
> > > > > This is essentially useful when you need to guarantee that process
> > > > > will stay suspended even if it's currently suspended waiting for
> > > > > semaphore signal.
> > > >
> > > > Do you mean to say that your processes resume running before their
> > > > semaphores are signaled?
> > > >
> > >
> > > Just try to run given code:
> > >
> > > | sema proc |
> > > sema := Semaphore new.
> > > proc := [ sema critical: [ Transcript show: 'Oopsie' ] ] fork.
> > > Processor yield.
> > > proc suspend.
> > > proc resume.
> > >
> <snip>
> No, i'm specially doing Processor yield to make proc start waiting for
> semaphore.


Er... oh, I see. From my point of view (which consists of little format
training wrt Process management), you're mis-treating these poor objects.
The code would work... but I'd never write code like that.

If you want to use #critical:, you should be making the Semaphore with "sema
:= Semaphore forMutualExclusion".

"Processor yield" shouldn't ever be used IMHO. It relies on particular
behaviour of the scheduler. In a future version of Squeak when we properly
support pthreads or we "improve" the behaviour of the scheduler, your code
might not work as expected.


> > I can't try this code at the moment - I don't have Squeak nearby.
> >
> > Generally, I'd rarely use Process>>suspend in my code. Semaphores
> provide
> > the behaviour that you want; a Semaphore is a linked list of waiting
> > processes. When you call #wait on a semaphore, your process gets added
> to
> > the list. When you call #signal, the process at one of the ends of the
> list
> > (FIFO? LIFO? Can't remember) gets resumed. The effect of #suspend and
> > #resume should have no effect on the signalled/waiting state of a
> Process.
> >
> > In the Launcher example that you give, it would be okay to use #suspend
> and
> > #resume, but there shouldn't be anything else in the image which is
> trying
> > to suspend or resume those processes.
> >
> Yes, i was using it like:
>
> suspendedList := OrderedCollection new.
> (Process allInstances select:[:proc | proc isActiveProcess not and: [
> proc isSuspended not ]]) do: [:proc | suspendedList add: proc. proc
> suspend].
>
> <... do my code...>
>
> suspendedList do: [:proc | proc resume ].
>
> But because of semaphores bug, after i sending #resume to processes
> which waiting on semaphore signal causing them think that signal is
> received.
> Btw you can try this code yourself and see how low space watcher pops
> up scaring you to death :)
>


I'll try this when I get home. I do a lot of multithreaded programming in
Squeak so its important to me that this stuff works right.

Gulik.

-- 
http://people.squeakfoundation.org/person/mikevdg
http://gulik.pbwiki.com/
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