Hi all,

I have a commercial application made with C,C++/Qt on Linux platform. The app collects data from different sensors and displays them on GUI. Each of the protocol for interfacing with sensors is implemented using singleton pattern and threads from Qt QThreads class. All the protocols except one work fine. Each protocol's run function for thread has following structure:

void <ProtocolClassName>::run()
{
while(!mStop)  //check whether screen is closed or not
{

mutex.lock()
  while(!waitcondition.wait(&mutex,5))
  {
   if(mStop)
      return;
  }

  //Code for receiving and processing incoming data

 mutex.unlock();
} //end while
}

Hierarchy of GUI.

1.Login screen. 2. Screen of action.

When a user logs in from login screen, we enter the action screen where all data is displayed and all the thread's for different sensors start. They wait on mStop variable in idle time and when data arrives they jump to receiving and processing data. Incoming data for the problem protocol is 117 bytes. In the main GUI threads there are timers which when timeout, grab the running instance of protocol using

   <ProtocolName>::instance() function

Check the update variable of singleton class if its true and display the data. When the data display is done they reset the update variable in singleton class to false. The problematic protocol has the update time of 1 sec, which is also the frame rate of protocol. When I comment out the display function it runs fine. But when display is activated the application hangs consistently after 6-7 hours. I have asked this question on many forums but haven't received any worthwhile suggestions. I Hope that here I will get some help. Also, I have read a lot of literature on Singleton, multithreading, and found that people always discourage the use of singletons especially in C++. But in my application I can think of no other design for implementation.

Thanks in advance

A Hapless programmer