Question

When a simple Thread is run with just an infinite loop in it causing 100% CPU, how come is this possible?

My thread call is as follows on a QEvent in Qt dialog class, Say on a button click.

  pthread_t thread_id;
  pthread_create( &thread_id, NULL, DataCollectionThread, (void*) this );

And my thread procedure is,

void* DataCollectionThread( void* pParam )
{
   ((m_DataCollection*)pParam)->m_ReadDatafromport();
   return NULL;
}

And this ReadData() contains…

while(1)
{
}

My requirement is collecting data from serial port and plot a graph continuously. But as the CPU usage is 100%, any hardware interrupt in between plotting cause the plotting to stall, as the CPU switches the task to handle interrupt.

I am calling this thread in a Qt::Dialog based class. I am pretty sure that nothing other than this is triggered. What’s wrong with this? Does a simple infinite loop causes 100% CPU consumption eh? Or Is there any problem with using pthread_create in Qt?

EDIT:For Jonathon Reinhart

This is the actual while loop

while( 1 )
    {

            while(( Dataisavailable))
            {
                 //push the read data to stack
            }



        if(!m_DataReadable)
            break;
      }

Answer 1

One simple hack to get around this: Go to sleep for (short) periods to let the CPU do other stuff. #include <ctime> and add somewhere in your loop:

struct timespec ts;
ts.tv_sec=0;
ts.tv_nsec=10000000; // 10 milliseconds
nanosleep(&ts, NULL);

Of course, it would be better if you could explicitly sleep until you have actual work to do (more input to read, a full queue to trim). But adding in short sleeps will probably be sufficient.

It might make sense to look into your m_pDataProvider object’s implementation. Check for or add a method allowing you to sleep until there’s more data. If you’re just reading from a character device (e.g. ttyS0), poll or select might be useful here.