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

Subject: Re: [Boost-users] boost::mutex::scoped_lock crashes on OSX
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-12-16 12:41:31

Le 15/12/2015 20:11, David Medine a écrit :
> 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

Hi,

I need more context. Could you provide the declaration where phase_mut_ 
is in and the destructor of this class as well as where are you calling

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

while on the destructor?

Vicente
>
> 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
>
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