[Vm-dev] Re: #ifCurtailed: multi-thread semantics

[Ben Coman]

On Mon, Feb 22, 2016 at 11:08 PM, Ben Coman <btc at openinworld.com> wrote:
> Just a curiousity. I learnt something new today...
> #ifCurtailed blocks are processed in the outer most thread.
>
>     Transcript clear; crShow: Processor activeProcess; show:' - outside'.
>      p1 :=
>      [    [   Transcript crShow: Processor activeProcess; show: ' - inside'.
>               1 second wait.
>           ] ifCurtailed: [ Transcript crShow: Processor activeProcess;
> show: ' - curtailed' . ]
>     ] newProcess priority: 41.
>     p1 resume.
>     p1 terminate.
> ==>
> a Process(304957184) in nil - outside
> a Process(680396800) in nil - inside
> a Process(304957184) in nil - curtailed
>
> This makes some sense since (I guess) the inside thread is terminated
> before the curtailed block executes.  However another curiousity...
>
>     Transcript clear; crShow: Processor activeProcess; show:' - outside'.
>      p1 :=
>      [   Transcript crShow: Processor activeProcess; show: ' - middle'.
>           p2 :=
>           [   [   Transcript crShow: Processor activeProcess; show: ' - inside'.
>                     1 second wait.
>                ] ifCurtailed: [ Transcript crShow: Processor
> activeProcess; show: ' - curtailed' .
>                2 seconds wait ]
>            ] fork.
>            3 second wait.
>     ] newProcess priority: 41.
>     p1 resume.
>     p2 terminate.
> ==>
> a Process(304957184) in nil - outside
> a Process(146580480) in nil - middle
> a Process(417340928) in nil - inside
> a Process(304957184) in nil - curtailed
>
> ...why does the curtailed block execute in outside thread rather than
> the middle thread which still exists?
>
> Also interesting is that if the curtailed code contains a wait, it
> blocks the whole UI.
>
> cheers -ben
>
> btw, I added...
>   Process>>printOn: aStream
>       super printOn: aStream.
>       aStream nextPutAll: '(' , self hash printString , ') in '.
>       suspendedContext printOn: aStream


Further curiosity, the #ensure block is executed by the 'inner' process...

    Transcript clear; crShow: Processor activeProcess; show:' - outside'.
    p1 :=
     [    [   Transcript crShow: Processor activeProcess; show: ' - inside'.
              1 second wait.
          ] ensure: [ Transcript crShow: Processor activeProcess;
show: ' - curtailed' . ]
    ] newProcess priority: 41.
    p1 resume.
    p1 terminate.
==>
a Process(959980800) in nil - outside
a Process(636470784) in nil - inside
a Process(636470784) in nil - curtailed

And wrapping an #ensure: around an #ifCurtailed: makes its block be
executed by the 'inner' process...

    Transcript clear; crShow: Processor activeProcess; show:' - outside'.
     p1 :=
     [    [   [   Transcript crShow: Processor activeProcess; show: ' - inside'.
                  1 second wait.
              ] ifCurtailed: [ Transcript crShow: Processor
activeProcess; show: ' - curtailed'  ]
          ] ensure: [ Transcript crShow: Processor activeProcess;
show: ' - ensure' . ]
    ] newProcess priority: 41.
    p1 resume.
    p1 terminate.
==>
a Process(959980800) in nil - outside
a Process(663403776) in nil - inside
a Process(663403776) in nil - curtailed
a Process(663403776) in nil - ensure


BUT!!!  Huh!?!?
The original example now has the curtailed block executed by the
'inside' process...

    Transcript clear; crShow: Processor activeProcess; show:' - outside'.
    p1 :=
     [    [   Transcript crShow: Processor activeProcess; show: ' - inside'.
              1 second wait.
          ] ifCurtailed: [ Transcript crShow: Processor activeProcess;
show: ' - curtailed' . ]
    ] newProcess priority: 41.
    p1 resume.
    p1 terminate.
==>
a Process(959980800) in nil - outside
a Process(329852416) in nil - inside
a Process(329852416) in nil - curtailed

cheers -ben