Re: Role of 'wait' in a parallel program

[Bruno Franco]

I see, 'later' itself sets up *Run.
Thanks Alex

On Wed, Mar 15, 2017 at 1:21 AM, Alexander Burger 
wrote:

> Hi Bruno,
>
> > Joh-Tob's question got me curious about parallel code in picolisp. I've
> > studied the example of 'later' in the documentation and I have an idea of
> > how it works, but I don't understand how 'wait' works inside of it.
> > I understand *what* it does, it makes sure that the child processes
> finish
> > before returning the value for the whole expression.
>
> Right.
>
> > But I don't understand
> > *how* it works because, in the form of 'wait' that is used, *Run should
> be
> > executed each time the prg returns false. Yet *Run is not set to any
> value
> > in the code.
>
> In fact, *Run' is set, because 'later' installs a 'task' listening at the
> pipe
> to the child process:
>
>   ...
>   (task (pipe (pr (prog . "@Prg")))
>  ...
>
>
> > Here's the code for reference:
> > : (prog1
> > (mapcan '((N) (later (cons) (* N N))) (1 2 3 4))
> > (wait NIL (full @)) )
> > -> (1 4 9 16)
> >
> > I would also appreciate if someone could check if my idea of what is
> going
> > on in the code is correct:
> >
> > First, mapcan is executed. For each element in (1 2 3 4) a child process
> is
> > started, and the result of each operation is stored in a cons pair:
> '(NIL).
> > Every cons pair is concatenated into a list, which looks like '(NIL NIL
> NIL
> > NIL) in this case. Note that the list is built *before* any of the child
> > processes is completed, and since concatenation is destructive the result
> > will be stored in the appropriate position in this list whenever the
> child
> > process is finished. (wait NIL (full @)) checks that all these processes
> > are done before ending the prog1.
>
> Yes, this is absolutely correct.
>
> ♪♫ Alex
> --
> UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
>

Re: Role of 'wait' in a parallel program

[Alexander Burger]

Hi Bruno,

> Joh-Tob's question got me curious about parallel code in picolisp. I've
> studied the example of 'later' in the documentation and I have an idea of
> how it works, but I don't understand how 'wait' works inside of it.
> I understand *what* it does, it makes sure that the child processes finish
> before returning the value for the whole expression.

Right.

> But I don't understand
> *how* it works because, in the form of 'wait' that is used, *Run should be
> executed each time the prg returns false. Yet *Run is not set to any value
> in the code.

In fact, *Run' is set, because 'later' installs a 'task' listening at the pipe
to the child process:

  ...
  (task (pipe (pr (prog . "@Prg")))
 ...


> Here's the code for reference:
> : (prog1
> (mapcan '((N) (later (cons) (* N N))) (1 2 3 4))
> (wait NIL (full @)) )
> -> (1 4 9 16)
> 
> I would also appreciate if someone could check if my idea of what is going
> on in the code is correct:
> 
> First, mapcan is executed. For each element in (1 2 3 4) a child process is
> started, and the result of each operation is stored in a cons pair: '(NIL).
> Every cons pair is concatenated into a list, which looks like '(NIL NIL NIL
> NIL) in this case. Note that the list is built *before* any of the child
> processes is completed, and since concatenation is destructive the result
> will be stored in the appropriate position in this list whenever the child
> process is finished. (wait NIL (full @)) checks that all these processes
> are done before ending the prog1.

Yes, this is absolutely correct.

♪♫ Alex
-- 
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