Qt线程设计生产者消费者

Question

The main thread is loading tasks into a queue. A worker thread is dealing with these tasks.

My code is like this:

//Core subclass a QThread
Core::AddTask()
{ ...
  mutex.lock();
  tasks.append(task);
  mutex.unlock();
  start();//which calls the run function
}

Core::RefreshTask()
{ ...
  mutex.lock();
  tasks.clear();
  mutex.unlock();
  // Calculate the new tasks...
  ...
  //foreach newly added task call
  AddTask();
}

Core::run()
{ ...
  while (1)
{
  finish = false;
  mutex.lock();
  tasks.dequeue();
  if (tasks.size() == 0)
    finish = true;
  mutex.unlock();
  ...
  if (finish)
     break;
}
}

However I found the worker thread failed to finish all the tasks because when the run function is being processed, it will not response to start() call. Then in the situation that: the run function is processing the last task and in the sametime AddTask is being called, then its start() call will do nothing. And the run() function finish and ignore the task.

I know a signal/slot mechanism could solve the problem. But I am forced to use the old QThread::run() style multithreading... Any suggestions how to properly write a producer consumer pattern in Qt?

Answer 1

I think you don't need call start() in Core::AddTask() . When you add new task to task list, you can send some kind of event message. It can be Qt signal, condition variable or something else.

Event loop works in separate thread and process tasks. If task list is empty, event loop waits for an event.