Re: [boost] [interprocess] atomic_write32 on GCC/x86/x68_64 lacks memory barrier

Subject: Re: [boost] [interprocess] atomic_write32 on GCC/x86/x68_64 lacks memory barrier
From: Lars Hagström (lars_at_[hidden])
Date: 2014-08-11 09:21:43

Thanks!

As I said, I'm not an assembly programmer. I can copy/paste though, which
lead to the verbosity. :-)

On Mon, Aug 11, 2014 at 2:34 PM, Peter Dimov <lists_at_[hidden]> wrote:

> Lars Hagström wrote:
>
>  inline void atomic_write32(volatile boost::uint32_t *mem, boost::uint32_t
>> val)
>> {
>>   __asm__ __volatile__ ( "" ::: "memory" );
>>   __asm__ (
>>            "xchgl %0, %1"
>>            : "+r" (val), "+m" (*mem)
>>            );
>>   __asm__ __volatile__ ( "" ::: "memory" );
>> }
>>
>
> This will work, but it's more verbose than it needs to be. You can put the
> __volatile__ and "memory" on the xchg asm statement and take out the two
> others.
>
> You'll also need to fix atomic_read32:
>
> {
>    uint32 r = *mem;
>
>    __asm__ __volatile__ ( "" ::: "memory" );
>    return r;
>
> }
>
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