Path: utzoo!attcan!uunet!nih-csl!helix.nih.gov
From: bert@helix.nih.gov (Bert Tyler)
Newsgroups: comp.windows.ms
Subject: Re: Non-Win App surrendering its time slice
Message-ID: <546@nih-csl.nih.gov>
Date: 8 Oct 90 14:07:43 GMT
Sender: news@nih-csl.nih.gov
Organization: National Institutes of Health, Bethesda
Lines: 37

> I have a program (UUPC) which makes a lousy application to run an
> Windows DOS window because it has an idle spin loop which soaks up
> a lot more CPU than it needs to.  
> 
> Is there a way for a non-Windows (Turbo C) application to gracefully
> surrender it's time slice?
>
> Likewise, is there a way for a non-Windows application to notify Windows
> that the application is entering a critical path and doesn't want to
> lose its time slice?
 
Drew, there is indeed a way for a DOS program to detect whether or not
it is running under Windows, and to both give up its time slice when idle
and grab the CPU during critical periods.  Sending this response through
the net because it is probably useful to a lot of people.  This info came
off the Interlink BBS network:
 
------------------- snip snip -------------------------------
 
KW>(And while were at it, folks, is there an easy way for a non-
KW>Windows app to tell it's running under Windows?)
Use this first to see if the rest are OK
                 MOV AX,1600h   ; Check for win386/win3.0 present
                 INT 2Fh
Return AL = 0 -> No Windows, AL = 80 -> No WIn386 mode
       AL = 1 or AL = FFh -> Win386 2.xx running
  else AL = Major version (3), AH = Minor version
--------------- Release time slice
                 MOV AX,352Fh   ; **** Release time slice
                 INT 2Fh        ; Let someone else run
Return code is AL = 80H -> service not installed, AL = 0 -> all OK
--------------- Enter critical section (disable task switch)
                 MOV AX,1681H   ; Don't tread on me!
                 INT 2Fh
--------------- End critical section (Permit task switching)
                 MOV AX,1682h
                 INT 2Fh