[Boost-users] segfault using boost::thread_specific_ptr

Subject: [Boost-users] segfault using boost::thread_specific_ptr
From: Michael P. Soulier (msoulier_at_[hidden])
Date: 2015-12-21 09:34:08

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