[Boost-users] boost::mutex::scoped_lock crashes on OSX

Subject: [Boost-users] boost::mutex::scoped_lock crashes on OSX
From: David Medine (dmedine_at_[hidden])
Date: 2015-12-15 14:11:38

I am using boost in a python extension and it is having some problems on 
OSX. Specifically, I use a mutex of type boost::mutex in both the 
constructor and destructor methods. The constructor goes fine and the 
destructor crashes. The code works perfectly well on both Windows and Linux.

When my class is building itself, it calls functions like this one a 
bunch of times:

void enter_headers_phase(bool phase_locked) {
         if (phase_locked) {
             boost::mutex::scoped_lock lock(phase_mut_);
             headers_to_finish_++;
         }
     }

where phase_mut_ is of type boost::mutex. When debugging in XCode, I see 
nice looking members for phase_mut_ at this point in the program:

phase_mut_ (boost::mutex)
     m (pthread_mutex_t)
         __sig (long)    1297437784    1297437784
         __opaque    char [56]    ""

Later, when I am destroying, I make a nearly identical call as before:

...

{
     boost::mutex::scoped_lock lock(phase_mut_);
     shutdown_ = true;
}

...

but now, my phase_mut_ looks like it has an apparently empty _sig member:

phase_mut_ (boost::mutex)
     m (pthread_mutex_t)
         __sig (long)
         __opaque (char [56])    ""

When we go down the line of the mutex code in boost and finally arrive 
at line 62 in boost/thread/pthread/mutex.hpp:

           ret = ::pthread_mutex_lock(m);

I get a segmentation fault: EXC_BAD_ACCESS

It seems like this is becausem->_sig is now empty for some reason, but I 
can not determine why (XCode's debugger won't let me 'watch' this 
variable) but it should certainly be the case that it doesn't get 
touched between the apparently successful constructor routines and now.

This all happens on OSX Yosemite. I am compiling my extension with 
LLVM6.1 and I have gnu++0x as the C++ language dialect and libc++ as the 
stdlib. I am linking statically to boost 1.57 which I built using this 
command:

sudo ./b2 -a cxxflags="-stdlib=libc++" linkflags="-stdlib=libc++" 
toolset=clang link=static link=shared threading=multi install 
--prefix=/opt/local --layout-tagged

THX!
-David