Date: Wed, 5 Jan 2000 10:37:43 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: Andris Pavenis <pavenis AT lanet DOT lv>
cc: Nicola Bortolotti <nbsoft AT libero DOT it>, djgpp AT delorie DOT com
Subject: Re: Commport problems in *two* Win95 dosboxes
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On Tue, 4 Jan 2000, Andris Pavenis wrote:

> > Second, amazingly enough, a DOS box in the background doesn't get
> > timer interrupts delivered to it.
> 
> My experience shows that it gets part of timer interrupts in background
> (my rough estimate is 20% or less depending on system load).

At the time, I tested this with a simple DJGPP program that uses
setitimer, installs a handler for SIGALRM, and increments a counter
each time the handler is called.  In the background, the counter
doesn't get incremented at all during a run of at least 10 seconds,
but as soon as I switch the focus to the DOS box, the counter begins
to change.

Of course, it's possible that 10 seconds aren't long enough, but if
the ratio was indeed 20%, I'd expect to get at least some of them.

Perhaps Windows treats protected-mode programs differently than
real-mode programs?

If anybody is interested, I can dig out that test program.