c++ - The conditional variable is not working but after adding std::cout, it is working -

my project consists of 2 threads: 1 main thread , other thread handles window content. so, when main thread wants ask windows update calls draw function follows:

void subapplicationmanager::draw() {    // 0 number of applications has finished draw counter   {     boost::lock_guard<boost::mutex> lock(subapplication::draw_mutex);     subapplication::num_draws = 0;   }    // draw sub applications.   (size_t = 0; < m_subapplications.size(); i++)     m_subapplications[i].signal_draw();    // wait until sub applications finish drawing.   while (true){     boost::lock_guard<boost::mutex> lock(subapplication::draw_mutex);     std::cout << subapplication::num_draws << std::endl;     if (subapplication::num_draws >= m_subapplications.size()) break;   }  } 

the draw function signals other thread new task received.

void subapplication::signal_draw() {    task = task::task_draw;   {     boost::lock_guard<boost::mutex> lock(task_received_mutex);     task_received = true;   }   task_start_condition.notify_all();  } 

the body of other thread follows. waits task arrive , start process:

void subapplication::thread() {    clock_t start_time, last_update;   start_time = last_update = clock();    //! creates sub application   init();    while (!done)                                                       // loop runs while done=false   {       // draw scene.  watch esc key , quit messages drawglscene()       if (active)                                       // program active?       {         // wait here, until update/draw command received.         boost::unique_lock<boost::mutex> start_lock(task_start_mutex);         while (!task_received){           task_start_condition.wait(start_lock);         }          // task received set false, next loop.         {           boost::lock_guard<boost::mutex> lock(task_received_mutex);           task_received = false;         }          clock_t frame_start_time = clock();          switch (task){         case task_update:           update();           break;          case task_draw:           draw();           swapbuffers();           break;          case task_create:           create();           break;          default:           break;         }          clock_t frame_end_time = clock();         double task_time = static_cast<float>(frame_end_time - frame_start_time) / clocks_per_sec;        }   } } 

the problem if run code is, never runs other thread task = task::task_draw; if add std::cout << "draw\n"; beginning of subapplication::draw(), work should. looking reason happening , usual way fix it?

boost::lock_guard<boost::mutex> lock(task_received_mutex); task_received = true; 

okay, task_received_mutex protects task_received.

    boost::unique_lock<boost::mutex> start_lock(task_start_mutex);     while (!task_received){       task_start_condition.wait(start_lock);     } 

oops, we're reading task_received without holding mutex protects it. prevents race 1 thread reads task_received while thread modifying it? lead deadlock.

also, have code claims "wait until sub applications finish drawing" there's no call wait function. spins rather waiting, awful.