Re: [boost] [thread] A simply static initializeable mutex

From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2006-10-30 07:18:51

From: Felipe Magno de Almeida

> On 10/30/06, Anthony Williams <anthony_w.geo_at_[hidden]> wrote:
>> Roland Schwarz <roland.schwarz_at_[hidden]> writes:
>> [snipped]
> 
>>> Do you mean: the object might be already zero initialized before
>>> the ctor runs? If yes: this is very dangerous to rely on!
>> 
>> No. This is required. The memory for an object with
>> static-storage-duration MUST be zero initialized prior to the
>> constructor running. 
> 
> It dont even matter, it *must* not have a constructor. Or else
> there'll be a race condition on the compiler's flag and multiple
> constructor calls.

Does this matter if all the constructor does is repeat the zero
initialization?  (Serious question.  The answer is not obvious to me).

Roland suggested a mutex which relied on the zero initialization of
static PODs.  He then listed a number of issues that maintaining POD
status introduces (like we can't eliminate copy constructors).  I
pointed out that actually ALL static objects are zero initialized, so we
could have a default constructor that does nothing or repeats the zero
initialization (which means we could create the mutex other than as a
object with other than static storage duration).

-- 
Martin Bonner
Martin.Bonner_at_[hidden]
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB24 6WZ,
ENGLAND Tel: [phone]