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