MSGPACK_ENABLE_GCC_CXX_ATOMIC - Failed #905
Description
When running cmake on the cpp_master branch on Ubuntu 18.04 I get a
-- Performing Test MSGPACK_ENABLE_GCC_CXX_ATOMIC
-- Performing Test MSGPACK_ENABLE_GCC_CXX_ATOMIC - Failed
The test code in CMakeLists.txt reads
#include <bits/atomicity.h>
int atomic_sub(int i) { return __gnu_cxx::__exchange_and_add(&i, -1) - 1; }
int atomic_add(int i) { return __gnu_cxx::__exchange_and_add(&i, 1) + 1; }
int main(int argc, char * argv[])
{
atomic_sub(1);
atomic_add(1);
}The culprit is that since quite some time the header is under
#include <ext/atomicity.h>
Looking through some old systems is see that
- up to gcc 4.1.1 I find
bits/atomicity.h - after gcc 4.6.3 I find
ext/atomicity.h
so the transition was somewhere between gcc 4.1.1 and 4.6.3. Ubuntu 18.04 has gcc version 7.5.0
The code compiles and tests without atomicity.h, hard to judge whether there are performance impacts.
In case atomic actions are important, it seems to me that std::atomic is the natural choice these days.
In closing the steps to reproduce (on an Ubuntu 18.04 system, likely on all current Ubuntu/Debian systems):
git clone https://github.com/msgpack/msgpack-c.git
cd msgpack-c
git checkout cpp_master
git checkout 70912ff
mkdir build
cd build
cmake -DMSGPACK_CXX17=ON ..