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boostorg / system

Boost.org system module
http://boost.org/libs/system
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Build using boost 1.80 fails, works with 1.79 #92

Closed jcbastosportela closed 2 years ago

jcbastosportela commented 2 years ago

From boost 1.79 this change starts causing the build to fail in our target system (B&R PLC).

This platform does not have threading, resulting in BOOST_NO_CXX11_HDR_MUTEX to be defined (in boost/config/stdlib/libstdcpp3.hpp).

In boost 1.80 boost/system/detail/config.hpp starts considering this for defining BOOST_SYSTEM_HAS_SYSTEM_ERROR and this is now not defined (in 1.79 was).

This causes the compilation error with gcc6.3, c++14 (simplified output):

...\boost\json\impl\parse.ipp:   :In function 'boost::json::value boost::json::parse(boost::json::string_view, std::error_code&, boost::json::storage_ptr, const boost::json::parse_options&)'
...\boost\json\impl\parse.ipp: (Ln: 46, Col: 10) error :no match for 'operator=' in 'ec = jec' (operand types are 'std::error_code' and 'boost::json::error_code {aka boost::system::error_code}')
...

NOTE forcing the flag BOOST_SYSTEM_HAS_SYSTEM_ERROR will result in this error to be fixed, but then starts failing in boost\system\detail\error_category_impl.hpp because mutex is not defined (remember that our target does not have threading enabled) and also in boost 1.80 when BOOST_SYSTEM_HAS_SYSTEM_ERROR is set std::mutex is used (was not in boost 1.79).

So, it seems that with the current configuration of boost, a target that has std::error but does not have std::mutex is not supported.

pdimov commented 2 years ago

One possible workaround on your side would be to supply a dummy <mutex> header that has std::mutex and std::lock_guard that do nothing.

The other option is for me to allow configuration via a macro, BOOST_SYSTEM_DISABLE_THREADS, that turns off the use of the mutex.

jcbastosportela commented 2 years ago

@pdimov thank you for the fast reply. Supplying a dummy <mutex> is something that occurred to me, however that is not very practical because the toolchain of our platform does have the <mutex> (in this same exact version: https://github.com/gcc-mirror/gcc/blob/releases/gcc-6.3.0/libstdc++-v3/include/std/mutex); however _GLIBCXX_HAS_GTHREADS is not defined, so mutex is not defined.

I could play with include paths and provide my own version of the <mutex> but that is something that I want to avoid for now. Meanwhile I can keep using boost 1.79.

How feasible is the second option? Do you think it is something we could see in for example boost 1.81 or boost 1.82? Or is our case something atypical that boost won't be willing to cover?

pdimov commented 2 years ago

Support for BOOST_SYSTEM_DISABLE_THREADS added in https://github.com/boostorg/system/commit/53c00841fc0d892bf43cda60e3ea2f05c4362b32. You can apply this patch on top of 1.80, or wait for 1.81.

jcbastosportela commented 2 years ago

This seems to fix the issue for me! Thanks @pdimov