Re: [boost] [thread] Can Boost.Thread use Boost.Atomic withoutfalling on a compatibility issue?

Subject: Re: [boost] [thread] Can Boost.Thread use Boost.Atomic withoutfalling on a compatibility issue?
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2013-01-14 13:26:57

On Jan 14, 2013, at 1:11 PM, "Peter Dimov" <lists_at_[hidden]> wrote:

> Howard Hinnant wrote:
>> There are a couple of places in libc++ that need to be retrofitted to use <atomic>.  In the cases where that retrofit is in a header (i.e. call_once), the retrofit will currently need to be protected by __has_feature(cxx_atomic) as clang shuts this feature off in C++03 mode.
> 
> Not very on-topic, but... what does it mean that clang shuts the feature off? I see in <atomic> that you issue an #error when !__has_feature(cxx_atomic), but what would happen if this is removed? Don't the C11 intrinsics work regardless? 

I have no idea.  I just checked the clang page and cxx_atomic appears to be undocumented.  There is also a documented __has_feature(c_atomic).

I just ran this test in C++03 mode:

#include <iostream>

int main()
{
    std::cout << __c11_atomic_is_lock_free(1) << '\n';
    std::cout << __has_feature(c_atomic) << '\n';
}

It outputs:

1
0

I'm not sure what to make of that, or how much it can be trusted.

Howard