c++ - boost failing to obtain lock -

i working on real-time music application. working boost library newbie. implemented producer/consumer relationship protected syncronizedqueue, implemented 18.11 , 18.12 sections of https://www.quantnet.com/cplusplus-multithreading-boost/. when parsing midi input following exception:

terminate called after throwing instance of 'boost::exception_detail::clone_impl <boost::exception_detail::error_info_injector<boost::lock_error> >' what():  boost::lock_error 

code parsing input in producer:

rtmidiin *midiin = new rtmidiin(); std::vector<unsigned char> message; int nbytes, i; double stamp; m_queue=queue;          // check available ports. unsigned int nports = midiin->getportcount(); if ( nports == 0 ) {     std::cout << "no ports available!\n";     goto cleanup; }  midiin->openport( 1 );  // don't ignore sysex, timing, or active sensing messages. midiin->ignoretypes( false, false, false );  // install interrupt handler function. done = false; (void) signal(sigint, finish);  // periodically check input queue. std::cout << "reading midi port ... quit ctrl-c.\n"; while ( !done ) {   stamp = midiin->getmessage( &message );   nbytes = message.size();   if(nbytes>0){     if((message.size()!=1)&&((int)message.at(0)!=137)){             ( i=0; i<nbytes; i++ )             std::cout << "byte " << << " = " << (int)message[i] << ", ";             if ( nbytes > 0 )             std::cout << "stamp = " << stamp << std::endl;             m_queue->enqueue("asd");     } } } 

it breaks on first time encounters:

m_queue->enqueue("asd"); 

when trying execute:

boost::unique_lock<boost::mutex> lock(m_mutex); 

any appreciated!

edit1:

this synchronizedqueue object. exception thrown when calling enqueue().

template <typename t> class synchronizedqueue { private:     std::queue<t> m_queue;                      // use stl queue store data     mutable boost::mutex m_mutex;                       // mutex synchronise on     boost::condition_variable m_cond;       // condition wait  public:      // add data queue , notify others     void enqueue(const t& data)     {         // acquire lock on queue             boost::unique_lock<boost::mutex> lock(m_mutex);         // add data queue         m_queue.push(data);             // notify others data ready         m_cond.notify_one();         } // lock automatically released here      // data queue. wait data if not available     t dequeue()     {          // acquire lock on queue         boost::unique_lock<boost::mutex> lock(m_mutex);         //lock();         // when there no data, wait till fills it.         // lock automatically released in wait , obtained          // again after wait         while (m_queue.size()==0) m_cond.wait(lock);          // retrieve data queue         t result=m_queue.front(); m_queue.pop();         return result;     } // lock automatically released here }; 

most times, when stumble on such issue, it's mutex got locked destroyed or wasn't constructed already. sure, queue, passing parser, constructed, when parser threads starts parsing? or might be, exit of loop containing queue local variable stopped? maybe can quick test , add d'tor queue , set breakpoint there.

regards torsten