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From: Jens Gustedt <Jens.Gustedt@loria.fr>
Newsgroups: comp.std.c,comp.lang.c
Subject: Re: The threading specs in the standard: a new catastrophe
Date: Sun, 10 Jul 2011 14:47:20 +0200
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To: Marcin Grzegorczyk <mgrzegor@poczta.onet.pl>
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Xref: x330-a1.tempe.blueboxinc.net comp.std.c:707 comp.lang.c:8067

Am 10.07.2011 00:02, schrieb Marcin Grzegorczyk:
> No such thing is implied in the draft Standard.  The reason is that some
> existing mutex implementations do not provide static initialization;
> most notably, under Win32, neither mutex objects nor critical section
> objects do (barring some tricks that may break if Microsoft decides to
> change the underlying implementation, again).

Hm, I first thought that a once_flag could be used to launch an
initializer function for such statically objects. As such this is not
possible, since the call_once interface doesn't allow the function
parameter to receive an argument.

But an implementation would have to provide call_once & Co. So you'd
have to have
- some sort of atomic read of the once_flag
- the potential to delay all but one threads that stumble into this
  simultaneaously
- the potential to have the very first thread call an initialization
  function

These ingredients could be used equally well to call an mtx_init and
cnd_init on statically initialized objects, I think. Performance cost
of such things should be minor.

Jens