Re: Idea: Multitasking graphical OS for the GS

["Jeff Blakeney" <jeff.blakeney@a2central.com.remove-109l-this>]

  To: Eric Rucker
On Fri, 2 Jan 2009 11:58:27 -0800, Eric Rucker wrote:

> Well, the Minix book suggests another way of doing things...
> essentially, having the program sleep, which means the OS stops giving
> it CPU time, until it receives a signal from the OS. This wouldn't be
> a running loop, the program would halt execution until the OS sent the
> signal, at which point the program would be sent into its signal-
> handling routine.
> 
> At least, that's what my 2 AM reading through that section gave me.

That's pretty much how Windows programs operate.  You create callback
functions that the operating system calls only when it has a message for
your program.  That call back then checks the message and acts on it.
The problem is that Windows sends the callback function EVERY message
that the operating system can generate for the windows and controls that
the application is using.  Even if the program only acts on 5% of the
messages, the callback routine is called and simply does nothing for the
other 95% of the messages.  For example, a push button in a window can
generate the following notification messages:

    BN_CLICKED
    BN_DBLCLK (also called BN_DOUBLECLICKED)
    BN_DISABLE
    BN_HILITE
    BN_KILLFOCUS
    BN_PAINT
    BN_PUSHED
    BN_SETFOCUS
    BN_UNHILITE
    BN_UNPUSHED

Under normal circumstances, I only care about whether the button has
been pushed so only act on the BN_CLICKED message.  However, my callback
function is still passed in the other 9 when they occur so my program is
given time to run simply to find out that the message passed in is not
something I'm going to act on.

What I propose is that the program should tell the operating system that
when it gets a BN_CLICKED message for particular push button in my
program, it should call my callback function.  That way, my callback
would never be called for the other 9 messages that I ignore anyway so
there would be less context switching.

By the way, the TaskMaster call on the IIgs helps somewhat with this but
its TaskMask is quite limited in what messages you can set it to not
return.