> I was wondering how I can introduce more concurrency in the problem.

It's not exactly trivial. The essential issue is to decide on what a good
default policy for concurrent programming by users is. In my understanding
it's simply too hard to constantly deal with locks, critical sections etc.
The policy that I ultimately settled upon was simply to define that programs
run until they are complete or they block (where blocking is defined as
"waiting on external event"). Interestingly, it seems that Scratch is
following the same idea which is maybe not so surprising - in the end that's
what the stepping policy does, just in a more general way (#step always runs
to completion or until it waits for the next #step event).

> I will try to see how I can make a workspace that does not create the
> deadlock and play with the solutions suggested by boris.

The real trick here is that you can't have the "scheduler process" (which
organizes the individual steps) do the work since if it does, it will block
and thusly fail to organize any other activities. IOW, you need to decouple
"step scheduling" from "step evaluation" - once you do that it'll work
nicely. Be warned though that getting the scheduling right has a few very
subtle implications which aren't obvious at all.

> I was wondering if other people using Morphic for simulation did not
> get the same problem

Well, at least me and John both ran into the problem and came up with very
similar solutions ;-)

Cheers,
  - Andreas

----- Original Message ----- 
From: "ducasse" <ducasse at iam.unibe.ch>
To: "The general-purpose Squeak developers list"
<squeak-dev at lists.squeakfoundation.org>
Sent: Saturday, January 31, 2004 11:57 PM
Subject: Re: Multi-thread Question in Morph?


> > Your problem is that the UI process (which is responsible for invoking
> > #step) waits for the promise to compute its value. However, that
> > promise
> > will only be evaluated upon the next step, which would have to be run
> > via
> > the UI process which blocks on the promise. In short, you have a
> > classic
> > deadlock.
>
> Yes I see that :). Naively I was thinking that Morphic was more
> concurrent.
> I was wondering how I can introduce more concurrency in the problem.
> I'm bit afraid by the idea of forking
> the stepping mechanism.
> I will try to see how I can make a workspace that does not create the
> deadlock and
> play with the solutions suggested by boris.
>
> I was wondering if other people using Morphic for simulation did not
> get the same problem
>
> Stef
>
>
> On 31 janv. 04, at 23:03, Andreas Raab wrote:
>
> > Hi Stef,
> >
> >
> > Cheers,
> >   - Andreas
> >
> > ----- Original Message -----
> > From: "ducasse" <ducasse at iam.unibe.ch>
> > To: "The general-purpose Squeak developers list"
> > <squeak-dev at lists.squeakfoundation.org>
> > Sent: Sunday, February 01, 2004 1:52 AM
> > Subject: Multi-thread Question in Morph?
> >
> >
> >> Hi all
> >>
> >> I'm designing a simple environment with a bot evolving in a maze. The
> >> user can control the bots from a kind of workspace.
> >> In an old implementation, I did not use step and put some delay and
> >> World doOneCycle. Not so good. I decided to
> >> clean that and  to use the step method to execute commands sent to
> >> this
> >> morph.
> >>
> >>
> >> The morph has a queue of actions (which are reified message sends with
> >> a future to hold their result).
> >>
> >> For example the method go is implemented as
> >> NewBot>>go
> >>
> >> self addAction: #goPrimitive
> >>
> >> this means that when the action is executed the method goPrimitive
> >> will
> >> be executed which is in fact implemented.
> >>
> >> goPrimitive
> >>
> >> self position: (self position + (10 at 10))
> >>
> >> addAction: and similar methods are implemented that way: a command
> >> object is created and put in the queue and returned.
> >>
> >> addAction: aSelector arguments: anArray
> >>
> >> | anAction |
> >> anAction := (BotCommand selector: aSelector arguments: anArray).
> >> actionQueue addLast: anAction.
> >> ^ anAction
> >>
> >> A command object is a message reification that holds a future so that
> >> I
> >> can get result back to the sender when necessary (for exmaple getter
> >> method, as in the following example. result in that case get the
> >> future
> >> and ask its value.
> >>
> >> diamNumber
> >>
> >> ^ (self addAction: #diamNumberPrimitive) result
> >>
> >> The step method goes over the queue and execute the actions one after
> >> the other. It then puts the future value
> >>
> >> step
> >>
> >> | action res |
> >> ^ actionQueue isEmpty
> >> ifFalse: [action := self removeAction.
> >> res := self perform: action selector withArguments: action
> >> arguments.
> >> action setFutureValue: res]
> >>
> >>
> >> Now I have the following problem that you can try just by loading the
> >> cs.
> >> If I create a morph NewBot new openInWorld, inspect it and execute
> >> self
> >> diamNumber in an inspector, the complete environment
> >> is blocked.
> >>
> >> I simplified the problem to its essence in the attached file. If you
> >> open an inspect and evaluate self diamNumber
> >> the system freezes. Apparently there is not enough thread in morphic.
> >> So I started to see where I could
> >> put another thread. The problem is that
> >> - in an inspector doing [self diamNumber] fork does not help because I
> >> would need another future to get the value form the thread
> >> - opening an inspector in another block (self inspect fork) and in
> >> this
> >> new inspector doing self diamNumber still freezes the system
> >> My impression is that the UI scheduler does not let me doing that.
> >>
> >>
> >>
> >
> >
> > ----------------------------------------------------------------------- 
> > -----
> > ----
> >
> >
> >>
> >>
> >> does anybody has an idea of how I could solve that problem?
> >>
> >>
> >>
> >> stef
> >
> >
> > ----------------------------------------------------------------------- 
> > -----
> > ----
> >
> >
> >>
> >>
> >
> >
>
>