Re: [boost] [thread] Use of _ReadWriteBarrier

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-10-08 08:21:21

Anthony Williams wrote:
> John Maddock <john <at> johnmaddock.co.uk> writes:
>
>> Just a couple of quick questions/comments regarding the use of
>> _ReadWriteBarrier in the latest Boost.Thread code:
>>
>> First up _ReadWriteBarrier is a VC++ compiler intrinsic: it's not
>> supported by the Borland or MingW compilers, so these fail to link
>> with unresolved externals to _ReadWriteBarrier.  Can
>> interlocked_read_acquire be written in terms of
>> InterlockedCompareExchange(pointer, 0, 0) and
>> InterlockedCompareExchangePointer(pointer-to-pointer, 0, 0) in these
>> cases?
>
> Yes, that's top of my list for this morning.

_ReadWriteBarrier stops the compiler from reordering. Going to a 
non-intrinsic InterlockedCompareExchange will also have this effect, but it 
might be possible to achieve it in another (cheaper) compiler-specific way; 
__asm__ ( :::"memory" ) is the GCC equivalent. Borland may already not 
reorder across a volatile read; this needs to be tested.