Re: [Boost-users] segfault using boost::thread_specific_ptr

Subject: Re: [Boost-users] segfault using boost::thread_specific_ptr
From: Juan Ramírez (jramirez.uy_at_[hidden])
Date: 2015-12-21 10:04:48

tls_buffer is not initialized, thread_specific_ptr will not allocate memory
for you (it will call delete on thread exit tough)

if (!tls_buffer) {
   tls_buffer.reset(new std::stringstream());
}

The previous must be done before any attempt to use that variable

On Mon, Dec 21, 2015 at 11:34 AM, Michael P. Soulier <
msoulier_at_[hidden]> wrote:

> Hello,
>
> I’m trying to implement a thread-safe logger that uses a
> boost::thread_specific_ptr to a std::stringstream as a logging buffer.
>
> static boost::thread_specific_ptr<std::stringstream> tls_buffer;
>
> class MLoggerHandler
> {
> public:
>     MLoggerHandler(boost::mutex& mutex, std::ostream& ostream);
>     ~MLoggerHandler();
>     void setLevel(int level);
>
>     template <class T>
>     // For handling << from any object.
>     MLoggerHandler& operator <<(T input) {
>         std::cerr << "Adding to buffer" << std::endl;
>         if (m_start) {
>             *tls_buffer << localDateTime() << " " << input;
> <================= SEGFAULT
>             m_start = false;
>         }
>         else {
>             *tls_buffer << input;
>         }
>         std::cerr << "On buffer: " << tls_buffer->str() << std::endl;
>         return *this;
>     }
>     // For handling std::endl
>     std::ostream& operator <<(std::ostream& (*f)(std::ostream&)) {
>         std::cerr << "Flushing buffer" << std::endl;
>         m_start = true;
>         std::ostream& rv = f(m_ostream);
>         m_mutex.lock();
>         m_ostream << tls_buffer->str();
>         m_mutex.unlock();
>         tls_buffer->str("");
>         return rv;
>     }
> private:
>     // A flag to indicate the beginning of a new line.
>     bool m_start = true;
>     // A mutex passed in from the main logger for synchronization.
>     boost::mutex& m_mutex;
>     // The logging level.
>     int m_level;
>     // The output stream.
>     std::ostream& m_ostream;
>     // Return the current date and time as a localized string.
>     const std::string localDateTime();
> };
>
> The initial idea, was to flush the buffer and write when a terminating
> std::endl was encountered. But, just trying to dereference the pointer and
> write to the std::stringstream is crashing. Do I need to initialize the
> std::stringstream, or is it initialized in constructor?
>
> Thanks,
> Mike
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users

-- 
Juan
:wq