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From: ralf@b.gp.cs.cmu.edu.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Limits on MSDOS file handles
Message-ID: <9@b.gp.cs.cmu.edu>
Date: Fri, 20-Feb-87 23:14:21 EST
Article-I.D.: b.9
Posted: Fri Feb 20 23:14:21 1987
Date-Received: Sat, 21-Feb-87 16:21:15 EST
References: <1511@im4u.UUCP>
Distribution: world
Organization: Carnegie-Mellon University, CS/RI
Lines: 46

In article <1511@im4u.UUCP> jai@im4u.UUCP (Jai Srinivasan) writes:
>
>>Closing inherited handles (standard or otherwise) is freeing them up both
>>towards the program limit (20) and the total limit (FILES). In your case,
>>though, closing only two handles just wasn't enough. Consider that if PROCOMM
>>has 5 non-preset handles opened, it is already occupying 10 handles (5 standard
>>plus 5 more)! Another two (or more) go to the COMMAND.COM that started your
>>PROCOMM, and there isn't that much left.
>>
>
>That still does not explain the anamoly.  I should have mentioned that
>the program, when run from ProComm, always succeeded in opening one
>file and then failed to open the next one.  If the above is correct
>(closing a file frees the handle for both the program and the system
>limit), the program should have run with stdaux and stdprn closed as 2
>files were being closed in an attempt to open one.  But closing stdprn
>and stdaux made no difference: it yet opened one and failed to open the
>next.
>
>The conclusion would appear to be that closing standard files (or at
>least stdprn and stdaux) does not free handles for the system limit.
>Anyone care to comment?

That is exactly correct, since the standard files are inherited from the
process which loads the current process.  When a program is loaded with
DOS function 4BH, it inherits all of the currently open files (this is what
allows the COMMAND.COM I/O redirection operators < and >).  While the
new process has its own file handles for them, internally they refer to the
same file descriptor.  Thus closing handles is like deleting files in UN*X:
the DOS-internal file descriptor is only freed when the last handle referencing
it it closed.

>Jai Srinivasan, UUCP: {gatech,harvard,ihnp4,pyramid,seismo}!ut-sally!im4u!jai
>ARPA:  		      jai@im4u.UTEXAS.EDU, jai@sally.UTEXAS.EDU

Ralf Brown
ARPA:  RALF@B.GP.CS.CMU.EDU
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