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From: stoeen@solan.unit.no (Asbj|rn St|en)
Newsgroups: comp.os.msdos.programmer
Subject: Re: TSR PROGRAMMING PROBLEM
Message-ID: <1991Jan29.233201.21253@ugle.unit.no>
Date: 29 Jan 91 23:32:01 GMT
References: <1991Jan26.195955.12946@ugle.unit.no> <1991Jan26.220820.7855@uwasa.fi> <8256@ucdavis.ucdavis.edu> <1991Jan29.173752.10045@bronze.ucs.indiana.edu>
Sender: news@ugle.unit.no
Reply-To: stoeen@solan.unit.no (Asbj|rn St|en)
Organization: Norwegian Institute of Technology
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In article <1991Jan29.173752.10045@bronze.ucs.indiana.edu>, yawei@bronze.ucs.indiana.edu (mr. yawei) writes:

|> This is called the DOS re-entrancy problem which anyone who is teaching
|> you to write TSRs should have told you about. Simply speaking, DOS
|> cannot be entered twice. Since the int 16h request most likely comes
|> from inside DOS, issuing another DOS call destroys the stack of the
|> first call thus causing the system to crash. (Actual situation is more
|> complicated since DOS uses several stacks. Try to get some books on this
|> subject. Unfortunately, I can't think of any good books on writing
|> TSRs. Has anyone seen one?)

Maybe I am wrong, but I thought that most basic character device DOS functions
*were* reentrant... It is true that more complex functions (file, disk handling) are
not reentrant. Certainly, function 05H should be okay to call.
Perhaps someone out there knows more about this...

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