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From: jrv@siemens.UUCP
Newsgroups: net.micro.pc
Subject: Re: DOS re-entrancy
Message-ID: <23900011@siemens.UUCP>
Date: Thu, 6-Mar-86 09:21:00 EST
Article-I.D.: siemens.23900011
Posted: Thu Mar  6 09:21:00 1986
Date-Received: Sun, 9-Mar-86 00:04:09 EST
References: <103@nvuxr.UUCP>
Lines: 26
Nf-ID: #R:nvuxr:-10300:siemens:23900011:000:899
Nf-From: siemens!jrv    Mar  6 09:21:00 1986




There is a flag buried in the internal data area for MS-DOS called INDOS.
A 0 value indicates that MS-DOS is not currently executing in a critical
section. Any other value indicates that you can not make a Int 21 call.

To find out the current value of this flag:

	1. Before interrupt processing starts execute the GET_INDOS_FLAG
	   function. This is function 34h in MS-DOS.
	   (i.e. AX = 34h when doing the Int 21)

	2. Upon return you don't get the flag but rather a pointer to
	   it in ES:BX.  ES = the segment address and BX = the offset
	   address of the INDOS flag.

	3. When the interrupt occurs directly test this byte from the
	   interrupt handler to determine if calls to MS-DOS are
	   allowable. You will have to determine appropriate actions
	   if the interrupt occurred during a critical section of MS-DOS.

Hope this helps.

Jim Vallino
{allegra,ihnp4}!princeton!siemens!jrv