From: broeker AT acp3bf DOT knirsch DOT de (Hans-Bernhard Broeker)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problems using signals
Date: 7 Oct 1999 17:56:43 +0200
Organization: RWTH Aachen, III. physikalisches Institut B
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References: <01BF10C3 DOT 98917580 AT tim DOT polyhedra DOT com>
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Tim Bedding (tim AT polyhedra DOT com) wrote:
> Due to a mistake, I ran a program containing
> a tight loop. This simple program did not explicitly define
> or call any signal functions.

> I could not interrupt the program using Ctrl-C.

> Is this to be expected? 

Yes. Unlike in a 'real' operating system, keyboard-generated signals
in MS-DOS don't generally get delivered until the point were a program
reads the keyboard, or does any other kind of I/O. The underlying
problem is that your program is in protected mode (almost) all the
time, i.e.  it doesn't call or use DOS at all. If DOS isn't doing any
work, it cannot detect the Ctrl-C keypress deliver an interrupt to
your program.

> Is there a way to program or compile in order to make sure that the
> program is always interruptable somehow?

The program is interruptible by another key, *if* that's the first key
you press: Ctrl-Break is translated to an interrupt request in the
BIOS (or keyboard processor, I'm not sure), and will be serviced
immediately, at all times. Same for Ctrl-Alt-Del (which may not do
what you actually want :-).

To get 'interruptability', just check for keypresses from time to
time.  (Every 'n'-th iteration of the inner loop, for some suitable
value of 'n').


-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.