VkBackground(3x)

NAME
     VkBackground - Support for simple work procedure-based background tasks

INHERITS FROM
     VkCallbackObject

HEADER FILE
     #include <Vk/VkBackground.h>

PUBLIC PROTOCOL SUMMARY
   Constructor/Destructor
           VkBackground(void);
           void ~VkBackground(void);


   Starting and Stopping
           void start(void);
           void stop(void);


PROTECTED PROTOCOL SUMMARY
           virtual Boolean timeSlice(void);


CLASS DESCRIPTION
          VkBackground is an abstract class that provides a simple C++
          interface to handling background tasks based on Xt work procedures
          (functions that are called whenever there are no events pending in
          the application's event queue).  VkBackground handles the details of
          registering a work procedure and provides a convenient way to
          maintain state between calls to the work procedure.



DERIVING SUBCLASSES
          The VkBackground class is intended to be subclassed. Derived classes
          must override the timeSlice() member function which behaves just
          like an Xt work procedure. This member function is called whenever
          no events are pending in the application's event queue. It is
          expected to perform a small amount of work and return quickly. The
          function must return TRUE if the class has completed its task is
          done, or FALSE if the member function should be called again.

          The primary for using this class instead of using a work procedure
          directly is the ability to store state in class data members between
          calls to the timeSlice() function.
FUNCTION DESCRIPTIONS
   timeSlice()
           virtual Boolean timeSlice(void);


          Called whenever no events are pending in the application's event
          queue.  This function must return quickly and return a value of TRUE
          if the class has completed its task and the member function should
          not be called again, or FALSE if it should be called again at the
          next possible time.

   VkBackground()
           VkBackground(void);


          Initialize a VkBackground object. The constructor does not start the
          work procedure.

   ~VkBackground()
           void ~VkBackground(void);


          Free all storage associated with a VkBackground object. If this
          object's work procedure is currently active, the destructor removes
          it.

   start()
           void start(void);


          Start the background task by installing a work procedure.

   stop()
           void stop(void);


          Stop the background task by removing any currently installed work
          procedure.

INHERITED MEMBER FUNCTIONS
SEE ALSO
     ViewKit Programmer's Guide
     The X Window System, DEC Press, Bob Sheifler and Jim Gettys
     The X Window System Toolkit, DEC Press, Paul Asente and Ralph Swick
     The OSF/Motif Programmers Reference, Prentice Hall, OSF