[M3devel] join twice?

[Tony Hosking]

OK, sure.  Fair enough.

On 2 Nov 2009, at 16:43, Jay K wrote:

>  > (Whether the implementation actually prohibits it or not is an  
> implementation decision.)
>
> Tony, I'm sympathetic to the smaller version but I think it is wrong.
> "It is a checked runtime error to call this more than once for any t"
> is a much different/stronger statement than e.g.
> "it is implementation defined what happens if you call join more  
> than once for any t".
> The printed Reactor 4.1 docs have the same comment as current  
> Thread.i3.
>
> You know, ideally if I write:
> Thread.Join(t);
> Thread.Join(t);
>
> and it works today on any system, it will continue to work on all  
> systems.
> I think "implementation defined" is something Modula-3 tries to have  
> less of.
>
> On the other hand, I think if we foresee it to work trivially on all
> forseeable implementations, we can change the interface by removing  
> the comment.
> Win32 WaitForSingleObject(thread, INFINITE) is allowed multiple  
> times, though
> that isn't the current implementation.
>
>  - Jay
>
> From: hosking at cs.purdue.edu
> To: jay.krell at cornell.edu
> Date: Mon, 2 Nov 2009 12:59:36 -0500
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] join twice?
>
> I don't know that there ever was a mandate that join can only be  
> called once on a given thread.  But, given that pthread_join is  
> undefined when called more than once on the same thread we probably  
> want to retain the comment.  (Whether the implementation actually  
> prohibits it or not is an implementation decision.)  The point is  
> that we should be free to give the error in some later  
> implementation, so as to not to restrict what semantics the  
> implementation must support.
>
> Antony Hosking | Associate Professor | Computer Science | Purdue  
> University
> 305 N. University Street | West Lafayette | IN 47907 | USA
> Office +1 765 494 6001 | Mobile +1 765 427 5484
>
>
>
>
> On 2 Nov 2009, at 10:11, Jay K wrote:
>
> Thread.i3:
>
>
> PROCEDURE Join(t: T): REFANY;
> (* Wait until "t" has terminated and return its result. It is a
>    checked runtime error to call this more than once for any "t". *)
>
>
> ThreadWin32.m3:
>
>
> PROCEDURE Join(t: T): REFANY =
>   VAR res: REFANY;
>   BEGIN
>     LOCK t DO
>       IF t.joined THEN Die(ThisLine(), "attempt to join with thread  
> twice"); END;
>       WHILE NOT t.completed DO Wait(t, t.join) END;
>       res := t.result;
>       t.result := NIL;
>       t.joined := TRUE;
>       t.join := NIL;
>     END;
>     RETURN res;
>   END Join;
>
> PROCEDURE AlertJoin(t: T): REFANY RAISES {Alerted} = similar
>
>
> ThreadPThread.m3:
>
>
> PROCEDURE Join (t: T): REFANY =
>   BEGIN
>     LOCK t DO
>       WHILE NOT t.completed DO Wait(t, t.join) END;
>     END;
>     RETURN t.result;
>   END Join;
>
> PROCEDURE AlertJoin (t: T): REFANY RAISES {Alerted} = similar
>
>
> Should we just loosen the comment and go with the simpler pthread  
> version?
> I'd like Win32 and pthread to be more similar where possible, to  
> ease maintenance.
>
>
>  - Jay
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://m3lists.elegosoft.com/pipermail/m3devel/attachments/20091102/2fd3f52d/attachment-0002.html>