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

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2006-10-30 05:00:44

Roland Schwarz <roland.schwarz_at_[hidden]> writes:

> Martin Bonner wrote:
>
>> You may be able to do a little better.  The standard says "The storage
>> for objects with static storage duration (3.7.1) shall be
>> zeroinitialized (8.5) before any other initialization takes place."
>> What is more, most normal operating systems give programs pages of
>> memory that are zero-initialized, so compilers would have to do work to
>> avoid this.
>
>> I think that means you can declare constructors and STILL have the
>> object well behaved.
>

> 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.

> 1) "Might": the standard does not require it.

Wrong.

> 2) E.g.: MSVC initializes memory to "CDCDCDCDCDCD...." in debugging
>     builds, so there is at least one prominent case where the
>     assumption is false.

It does this for automatic and heap-allocated objects (which is allowed). If
it did it for static objects, it would be non-conforming.

Anthony
-- 
Anthony Williams
Software Developer
Just Software Solutions Ltd
http://www.justsoftwaresolutions.co.uk