Segmentation fault: 11 while using boost mutex

Question

I implemented a lock macro based on boost mutex, the code is below:

#include <boost/thread.hpp>
#include <iostream>

#define LOCK(x) if(Lock _lock_=x){}else

class Mutex{
public:
    friend class Lock;

private:
    boost::mutex mutex_;

    void Lock(){
        mutex_.lock();
    };

    void Unlock(){
        mutex_.unlock();
    };
};

class Lock{
public:
    Lock(Mutex& mutex):mutex_(mutex){mutex_.Lock();};
    ~Lock(){mutex_.Unlock();};

    operator bool() const {
        return false;
    }

private:
    Mutex& mutex_;
};

void wait(int seconds)
{
    boost::this_thread::sleep(boost::posix_time::seconds(seconds));
}

Mutex mtx;

void thread()
{
    for (int i = 0; i < 5; ++i)
    {
        LOCK(mtx){
            wait(1);
            std::cout << "Thread " << boost::this_thread::get_id() << ": " << i << std::endl;
        }
    }
}

int main()
{
    boost::thread t1(thread);
    boost::thread t2(thread);
    t1.join();
    t2.join();
}

I compiled it in the Mac OS using clang++ -std=c++11 -stdlib=libc++ lock_raii.cc -lboost_system -lboost_thread . When I run it, there is a Segmentation fault: 11 .

What's the problem with it?

Answer 1

Aside of the fact that this method at least questionable, I do not see a problem with the code. gcc v4.7.0 on Linux does not have issues either (there is no segmentation fault). So you may not setup boost properly or have a bug somewhere. You should run your program under debugger and see where the problem occurs. In theory this code:

if(Lock _lock_=x){}else

could be compiled as:

if(Lock _lock_= Lock(x) ){}else

and invoking copy ctor and have double unlock on the mutex. To make sure this is not the issue make copy ctor for class Lock private.