Question

I’m trying to compile some software I’ve been writing in Linux that uses some fancy new C++0x features on my Mac. I used MacPorts to install the gcc45 package, which gave me /opt/local/bin/g++-mp-4.5, however this compiler doesn’t want to compile anything in <thread>. Eg I try to compile:

//test.cpp
#include <thread>

int main()
{
std::thread x;
return 0;
}

and get:

bash-3.2$ /opt/local/bin/g++-mp-4.5 -std=c++0x test.cpp 
test.cpp: In function 'int main()':
test.cpp:5:2: error: 'thread' is not a member of 'std'
test.cpp:5:14: error: expected ';' before 'x'

A quick look in /opt/local/include/gcc45/c++/thread shows that the std::thread class is defined, but is guarded by the following:

#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)

Again, this works perfectly on my Ubuntu machine, so what’s the proper way to enable the c++0x <thread> library under the MacPorts version of g++ 4.5 (g++-mp-4.5)? Failing that, is there anything I need to know (configure flags, etc.) before I go about compiling gcc 4.5 myself?

Update:
It doesn’t look like the SO community knows much about this, so maybe it’s time to go a little closer to the developers. Does anyone know of an official mailing list I could forward this question to? Are there any etiquette tips to help me get an answer?

Update 2:
I asked SO for another temporary solution here, and so I’m now just substituting the boost::thread libraries for the std ones. Unfortunately, there is no boost::future so this isn’t quite a full solution yet. Any help would still be greatly appreciated.

Answer 1

Actually <thread> library doesn’t work under Mac OS X because pthreads here don’t have some functions with timeouts (e.g. pthread_mutex_timedlock()). Availability of this functions have to be checked using _POSIX_TIMEOUTS macro but it’s defined to -1 in Mac OS X 10.4, 10.5 and 10.6 (I don’t know what’s about 10.7) and this functions are really absent in pthread.h.

The _POSIX_TIMEOUTS macro is checked during the configuration of libstdc++. If the check ends successfully _GLIBCXX_HAS_GTHREADS macro becomes defined. And <thread> contents become available with -std=c++0x.

libstdc++ really needs _POSIX_TIMEOUTS e.g. in std::timed_mutex class implementation (see <mutex> header).

To summarize, I think that <thread> would become available on Mac OS X when GCC’s gthreads or libstdc++ will implement pthread_mutex_timedlock() (and others) emulation or when this functions will be implemented in Mac OS X.

Or maybe there would be a way in the future C++ standard to query for language features (e.g. this timed functions and classes) and it will be possible to build libstdc++ with this features disabled. However I’m not very familiar with the future standard and have doubts about that feature.