[M3devel] Modula-3/C interop in Date/Time?

[Tony Hosking]

On 15 Apr 2010, at 19:17, Jay K wrote:

> Rodney, right, I was wondering about traced vs. untraced also. I think having a traced pointer point outside the traced heap is ok though. The data will never be collected, the pointer never updated.

There are assertions in the @M3paranoid collector that will complain if a reference outside the heap is not to a TEXT literal.  Those should be the only ones we see.  Correctness dictates that we use UNTRACED references (ADDRESS, UNTRACED REF...) here.

> If the untraced data were ever freed (such as e.g. unloading the .dll! Which people usually forget about as a scenario..) then the traced pointers would go stale and there'd be a safety problem.
>  
>  
> In either case I'm not "rewriting" it, because there is a "unified interface" between Posix and Win32, and I can't make it <*external*> in one but not the other, unless I fork the file, not particularly worthwhile.
>  
>  
>  - Jay
>  
> > Date: Thu, 15 Apr 2010 17:44:07 -0500
> > From: rodney_bates at lcwb.coop
> > To: m3devel at elegosoft.com
> > Subject: Re: [M3devel] Modula-3/C interop in Date/Time?
> > 
> > Since these pointer variables are initialized by
> > C code and their referents are also provided by C code
> > as global variables, shouldn't the type be untraced?
> > 
> > I suppose that, since they don't point into the traced
> > heap, the collector implementation we have would quietly
> > ignore them as roots. But that's relying on implementation-
> > dependent information.
> > 
> > Also, if someone created a field of type Date.TimeZone,
> > (or an array of them) in a traced-heap-allocated object,
> > which is a perfectly legitimate thing to do, what would
> > our collector do then?
> > 
> > 
> > 
> > Jay K wrote:
> > > Is this legal/correct?
> > > 
> > > 
> > > Date.i3:
> > & gt; TYPE TimeZone <: REFANY;
> > > VAR Local, UTC: TimeZone; (* granted, will maybe change these to extern *)
> > > 
> > > 
> > > Date.m3:　
> > > REVEAL TimeZone = BRANDED "Date.TimeZone" REF INTEGER;
> > > 　
> > > 
> > > DatePosixC.c:
> > > static const int Local = 0;
> > > static const int UTC = 1;
> > > extern const int const * const Date__Local = &Local;
> > > extern const int const * const Date__UTC = &UTC;
> > > 　
> > > 
> > > - Jay

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