Re: [boost] [lockfree] review

Subject: Re: [boost] [lockfree] review
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-08-24 16:27:11

on Wed Aug 24 2011, Alexander Terekhov <terekhov-AT-web.de> wrote:

> Dave Abrahams wrote:
>> 
>> All I'm saying here is that a C++11 default atomic int is equivalent to
>> an int, coupled with an associated mutex, where accesses to the int are
>> always protected by locking the associated mutex.  If you're seriously
>> disagreeing with *that*, please say explicitly on what grounds.
>
>   int i; mutex mi, 
>   int j; mutex mj;
>   
>   mi.lock();
>   i = 1;
>   mi.unlock();
>
>   mj.lock();
>   j = 2;
>   mj.unlock();
>
> can be transformed to
>
>   multi_lock(mi, mj); // deadlock free
>   j = 2;
>   i = 1;
>   mi.unlock();
>   mj.unlock();
>
> and thus result in reodering i = 1 and j = 2.
>
> With C++11 default atomics (SC) for i and j such reodering is
> prohibited.

As it is with C++11 mutexes, IIUC.  Another thread that locks the same
mutexes is not allowed to observe the write to j before the write to i.
If you have contrary evidence, please point to it.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com