ZZ>
  >         I'm currently using a WaitForMessage() routine
  > where in the routine I simply give up time slices to os/2
  > (This is in the dos version) and check for mouse activity,
  > and keyboard activity... now I know there is a better way
  > to do it through os/2 , but I have yet to learn it...
ZZ>

___-------------------------------------------------------------------------

Conference: Os2prog
  To: Phil Crown            Date: 10/22/1994
From: YOU                   Time:  9:51 am

PC>
  > while( 1 ) {
  >   rc = KbdCharIn( &ki, 1, 0 );
  >   DosSleep( 5 );  // give up time slices this drops the CPU usage from
  >                   // %100 to %5 in this example
      do_mouse_and_clock_stuff() ;
  > }
PC>

  Since you asked how else a program would be able to know when a key on
  the keyboard is hit, here's my multithreaded improvement on the above
  single-threaded design.

  Main thread :

         Initialise event_queue and start secondary threads ;
         for (;;) {
             event = event_queue.blocking_read () ;
             switch (event) {
                    case MOUSE : do_mouse(event) ; break ;
                    case KEYBOARD: do_keyboard(event) ; break ;
             }
         }

       So when there is no work to do this thread spends its time
       blocked reading the event queue.

  Secondary thread 1 :

         for (;;) {
             mouse_event = blocking_read_of_mouse () ;
             event_queue.post(mouse_event) ;
         }

       So when there is no work to do this thread spends its time
       blocked in the upper half of the mouse device driver.

  Secondary thread 2 :

         for (;;) {
             keyboard_event = blocking_read_of_keyboard () ;
             event_queue.post(keyboard_event) ;
         }

       So when there is no work to do this thread spends its time
       blocked in the upper half of the keyboard device driver.

  Secondary thread 3 :

         for (;;) {
             DosSleep(1000) ;
             update_clock_display () ;
         }

       This thread spends all of its idle time blocked within DosSleep() .

  Total CPU usage when there is no actual work to do ?  Well, since all
  threads are blocked, it must be zero.

  ( Incidentally, Peter Fitzsimmons will tell you that you can also page
    tune the program by putting the inner loops of the threads as close
    together as possible, reducing the working set of an idle process. )

  The only (slight) difficulty for the programmer is the event queue.
  This must support blocking reads, and all calls must be thread-safe.

  Although there is a message queue IPC facility provided by OS/2, it's
  possibly more expensive than rolling your own, since it has to use
  shared memory to ensure communication between processes.  For multiple
  threads within a single process, a global data structure can be used,
  and the only problem is synchronisation.  Fortunately, this happens to
  be the standard producer/consumer problem from most textbooks, and is
  easily solved using semaphores.

  Do you think that David Hamel is listening ?  (-:

  > JdeBP <

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