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From: karayan@nvuxr.UUCP (G J Karayannopoulos)
Newsgroups: net.micro.pc
Subject: DOS re-entrancy
Message-ID: <103@nvuxr.UUCP>
Date: Fri, 28-Feb-86 12:03:55 EST
Article-I.D.: nvuxr.103
Posted: Fri Feb 28 12:03:55 1986
Date-Received: Sat, 1-Mar-86 17:25:03 EST
Organization: Bell Communications Research, Piscataway, NJ
Lines: 21



I understand that there is a re-entrancy problem with DOS function 
calls (int 21h). In particular, if an application is interrupted 
WHILE making a DOS function call, by a hardware interrupt handler,
and the handler itself makes its own DOS function calls, then when
the handler returns, the original application cannot complete its
DOS function call. The reason is that int 21h is not re-entrant.

Is there any way around that? I know of one memory-resident program
that gets invoked by a particular combination of key strokes, but
if at the time you attempt to invoke it you are doind a DOS call,
the program will beep and refuse to operate. My question is this:
How does the resident program KNOW that a DOS function call was made
when it was invoked? Is there some DOS flag that one can test to see
if int 21h was running? I would appreciate any ideas or info.
Thanks in advance.


					George Karayannopoulos