[M3devel] pthreads tls initialization?

[Tony Hosking]

Sorry, yes, you are correct that the value NULL will also be NIL.  So,  
setspecific NIL is unnecessary.

In any case, I do think we should just move the handler stack into  
Activation and pare things back to just the one threadlocal per thread.

On 19 Mar 2009, at 12:02, Jay wrote:

> But doesn't pthread_create make it so? (More so, it makes it so on  
> any new threads.)
> Or it that not portable? Or did I misunderstand the opengroup web  
> page? Or other?
> Or, is this because, like, the Modula-3 notion of "NIL" might not  
> match the pthread notion of "NULL"? I don't believe in that extreme  
> level of portability/disbelief/theory, but...
> Unless someone can tell me about such a system.. in which
>  void* p = 0;
>  printf("%p\n", p);
>  memset(&p, 0, sizeof(p));
>  printf("%p\n", q);
>
> doesn't print two identical lines.
>
> I know the C standard does not guarantee this, and probably  
> therefore Modula-3 doesn't either, but I've never heard of a system  
> on which this isn't true.
> It seems more theoretical than, say, non-IEEE floating point math  
> (which I believe exists on VAX), or, say, 16 bit integers...
>
>  - Jay
>
>
> > From: hosking at cs.purdue.edu
> > To: jay.krell at cornell.edu
> > Date: Thu, 19 Mar 2009 10:22:59 +1100
> > CC: m3devel at elegosoft.com
> > Subject: Re: [M3devel] pthreads tls initialization?
> >
> > The setspecific call is to initialize the handler stack to nil. It  
> is
> > needed.
> >
> > On 19 Mar 2009, at 01:33, Jay wrote:
> >
> > >
> > > http://www.opengroup.org/onlinepubs/000095399/functions/pthread_key_create.html
> > >
> > >
> > > says that thread locals start as zero, but ThreadPThread.m3 does:
> > >
> > >
> > > PROCEDURE InitHandlers () =
> > > BEGIN
> > > WITH r = pthread_key_create_handlers() DO END;
> > > WITH r = pthread_setspecific_handlers(NIL) DO END;
> > > initHandlers := FALSE;
> > > END InitHandlers;
> > >
> > >
> > > Any reason for that setspecific call?
> > >
> > >
> > > I ask because I think some of this code should just be written  
> in C.
> > > But ideally then, the Win32 code should be too.
> > > So I'm just reading them, and they differ oddly in that pthread
> > > keeps doing like:
> > >
> > >
> > > if not initialized Initialize()
> > >
> > >
> > > and Win32 allocates its thread up front locals via the Modula
> > > initializer.
> > > Maybe pthread_key is very expensive, and avoided in single  
> threaded
> > > apps?
> > > But there aren't any, right, because the runtime creates  
> threads, at
> > > least one for the garbage collector?
> > >
> > >
> > > - Jay
> >

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