Monitoring a variable or an object changed asynchronously by a Callback function

[sirop]

I have a C style callback function for DDE communication, called asynchronously.
It works as it should.

Now I want this function to have a QBuffer or QLinkedList or at least an integer iterator
that should get a new value each time this callback function is executed.

I want to monitor the change of QBuffer from within my main function.

I could use void QIODevice::bytesWritten(qint64 bytes), but Signals and Slots are said to be ten times slower than callbacks.

Or shall I just implement a loop in my main function like this:

while (true)
{
  if myBuffer.changed()
      doSomething();
 
  QThread::msleep(SomeMilliseconds);
}

while (true)
{
  if myBuffer.changed()
      doSomething();

  QThread::msleep(SomeMilliseconds);
}

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BTW, shall my QBuffer be a static variable?