Performing Background Processing Without Using Timers

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

A Windows-based application that performs a long, background task, such as repaginating a word processing document, can be designed in a number of different ways.

A polling task can be accomplished by setting a timer to fire at the desired interval. Many nonpolling tasks can be performed in pieces. Although Windows does not have a method to schedule processing based on overall system load, an application can wait until there are no other messages to be processed by that application before proceeding. This article discusses the code required to implement this method.

NOTE: This polling method is unneccesary for native Win32 applications.

MORE INFORMATION

It is important that each piece of the task be relatively small. This allows Windows to devote processing time to other applications running in the system. Similarly, once the task is complete, it is important that the application signal that it is idle. This allows Windows to optimize its performance and to prolong battery life on portable computers.

The following code skeleton demonstrates how this might be implemented:

WinMain { do application initialization

fBackgroundToDo = TRUE; fRunning = TRUE;

while (fBackgroundToDo && fRunning)

     {
     if (fBackgroundToDo)
          {
          if ((PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
               {
               if (msg.message == WM_QUIT)
                    {
                    fRunning = FALSE;
                    break;
                    }

               TranslateMessage(&msg);
               DispatchMessage(&msg);
               }
          else
               fBackgroundToDo = DoABitOfBackground();
          }
     else if ((fRunning = GetMessage(&msg, NULL, NULL, NULL)) != 0)
          {
          TranslateMessage(&msg);
          DispatchMessage(&msg);

          fBackgroundToDo = IsThereBackgroundToDo();
          }
     }

For additional information on this topic, query on the following words in this Knowledge Base:

   SpawnAndWait