id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
10942,Boost.Thread fails to build on Cygwin,Peter Dimov,Steven Watanabe,"By default on Cygwin, the Boost.Thread headers choose the POSIX API. This decision is made in `boost/thread/detail/platform.hpp`:

{{{
#if defined(BOOST_THREAD_POSIX)
#  define BOOST_THREAD_PLATFORM_PTHREAD
#else
#  if defined(BOOST_THREAD_WIN32)
#       define BOOST_THREAD_PLATFORM_WIN32
#  elif defined(BOOST_HAS_PTHREADS)
#       define BOOST_THREAD_PLATFORM_PTHREAD
#  else
#       error ""Sorry, no boost threads are available for this platform.""
#  endif
#endif
}}}

In the Cygwin case, neither `BOOST_THREAD_POSIX` nor `BOOST_THREAD_WIN32` appear to be defined, but `BOOST_THREAD_CYGWIN`, so the logic above chooses `BOOST_THREAD_PLATFORM_PTHREAD`.

This is actually correct, in my opinion; Cygwin is a POSIX platform.

However, the Jamfile by default chooses Win32 on Cygwin:

{{{
local rule default_threadapi ( )
{
    local api = pthread ;
    if [ os.name ] = ""NT"" { api = win32 ; }
    return $(api) ;
}
}}}

which later results in a bunch of errors when `win32/thread.cpp` is compiled against `pthread/thread_data.hpp` et al.

So, either the default in `platform.hpp` should be changed to Win32 under Cygwin, or (better) the default `threadapi` in the Jamfile should be changed to `pthread` under Cygwin.

Manually specifying `threadapi=pthread` is not a particularly good option, because Boost.Thread is a dependency of some tests, and when

{{{
b2 toolset=gcc,gcc-cxx11,clang,clang-cxx11,msvc-8.0,msvc-10.0,msvc-11.0,msvc-12.0
}}}

(for example) is invoked to test a library, `threadapi=pthread` is not possible.",Bugs,new,To Be Determined,build,Boost 1.57.0,Problem,,,