Re: [boost] [thread] Can Boost.Thread use Boost.Atomic without falling on a compatibility issue?

Subject: Re: [boost] [thread] Can Boost.Thread use Boost.Atomic without falling on a compatibility issue?
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-01-13 13:41:10

On Sun, Jan 13, 2013 at 10:32 PM, Vicente J. Botet Escriba
<vicente.botet_at_[hidden]> wrote:
>
> Well, the definition removes the copy constructor and the assignment
>
> struct once_flag
> {
> BOOST_THREAD_NO_COPYABLE(once_flag)
>
>
> After adding
>
> static boost::once_flag once2 = BOOST_ONCE_INIT;
>
> to example/once.cpp
>
> and I'm seen the following kind of error on a lot of C++11 compilers

Does this mean that BOOST_ONCE_INIT is not supported and tested with
C++11 compilers? Seems an oversight to me.

> Maybe it is worth to add a portable extension to the C++11 to ensure
> compatibility.

This would be very useful, IMHO, since the same code could be used for
both C++03 and C++11.

> BTW, couldn't the lock scope be reduced as follows
>
> BOOST_THREAD_DECL void commit_once_region(once_flag& flag) BOOST_NOEXCEPT
> {
> atomic_type& f = reinterpret_cast< atomic_type& >(flag.storage);
> { // ++++++++
> pthread::pthread_mutex_scoped_lock lk(&once_mutex);
> f.store(initialized, memory_order_release);
> } // ++++++++
> BOOST_VERIFY(!pthread_cond_broadcast(&once_cv));
>
> }

No, this is not correct because this would lead to missed
notifications. Condition variables should always be used under the
locked mutex.