A worker thread in MFC is used for many background tasks like printing, computations, network servers etc.,  Unlike User Interface threads, worker threads do not have their own Message Maps.

  A worker thread in an MFC program can be implemented with a simple controlling function of the following declaration type.

    UINT Controlling_function_name(void parameter);

AfxBeginThread:

   Worker threads are created by calling the function AfxBeginThread. This function has two signatures. One for creating user interface threads and the other for creating a worker thread. The AfxBeginThread for worker thread takes the function name as the first parameter. The function passed as a parameter to the AfxBeginThread function will then be used for running as a separate thread.

MFC Worker Thread Sample - AfxBeginThread:

   This article explains the worker thread with a Dialog based application.   

1. Start by creating a MFC Dialog based application with name as WorkerThread.
2. After generating the necessary files, open the WorkerThreadDlg.cpp and copy/paste the following code.
   
   UINT WorkerThreadProc( LPVOID Param ) //Sample function for using in AfxBeginThread
   {
      CFile file;
      file.Open("C:\\Temp\\test.txt",CFile::modeCreate|CFile::modeWrite);
      CString strValue;
      for(int i=0;i<=100;i++)
      {
         strValue.Format("Value:%d",i);
   
         file.Write(strValue,strValue.GetLength()); // Write to the file for worker thread using AfxBeginThread
      }
      file.Close();
   
      return TRUE;
   }
   
3. In one of the dialog commands, call the AfxBeginThread as follows. For the sake of simplicity this article uses it in the OnOK function.
   
   void CWorkerThreadDlg::OnOK() 
   {
      // TODO: Add extra validation here
      AfxBeginThread(WorkerThreadProc,NULL,THREAD_PRIORITY_NORMAL,0,0,NULL);
      MessageBox("Thread Started");
   }
   
4. Now Build and run the application. If the OK button is clicked, it will write the data into a file.

   Actually speaking this sample does not truly use a multi-threaded situation. But still it tries to explain how the AfxBeginThread can be used to create a worker thread.

  The sample code explains how to create a worker thread with the above code samples.