id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
13121	std_fenced_block gets used for g++ 4.6.4 and hence buggy std::atomic_thread_fence	Richard Hazlewood <boost@…>	chris_kohlhoff	"With g++ 4.6.4: using {{{asio}}} code that results in {{{detail::fenced_block}}} being used results in {{{detail::std_fenced_block}}} being used.
This uses {{{std::atomic_thread_fence}}} but that has link issues with 4.6 (maybe https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51038).

{{{g++4.6 -std=c++0x -I boost... }}}

{{{
#include <boost/asio/detail/fenced_block.hpp>

#ifdef BOOST_ASIO_HAS_STD_ATOMIC
# pragma message(""Will use asio std_fenced_block"")
#endif

int main(int argc, char *argv[])
{
  (void)argc; (void)argv;

  boost::asio::detail::fenced_block block(boost::asio::detail::fenced_block::full);
}
}}}

boost_asio.cpp:4:51: note: #pragma message: Will use asio std_fenced_block
/tmp/ccNS0287.o: In function `boost::asio::detail::std_fenced_block::std_fenced_block(boost::asio::detail::std_fenced_block::full_t)':
boost_asio.cpp:(.text._ZN5boost4asio6detail16std_fenced_blockC2ENS2_6full_tE[_ZN5boost4asio6detail16std_fenced_blockC5ENS2_6full_tE]+0x22): undefined reference to `std::atomic_thread_fence(std::memory_order)'
/tmp/ccNS0287.o: In function `boost::asio::detail::std_fenced_block::~std_fenced_block()':
boost_asio.cpp:(.text._ZN5boost4asio6detail16std_fenced_blockD2Ev[_ZN5boost4asio6detail16std_fenced_blockD5Ev]+0x13): undefined reference to `std::atomic_thread_fence(std::memory_order)'
collect2: ld returned 1 exit status


It looks like between 1.63 and 1.64, in ''detail/fenced_block.hpp'', the {{{#elif defined(BOOST_ASIO_HAS_STD_ATOMIC)}}} line takes precedence over the specific gcc test.  However, {{{BOOST_ASIO_HAS_STD_ATOMIC}}} is defined for 4.6.4.
"	Bugs	new	To Be Determined	asio	Boost 1.64.0	Problem		g++ 4.6