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2167

Category: DOS kernel

INT 21 - DOS 3.3+ - SET HANDLE COUNT

	AH = 67h
	BX = size of new file handle table for process
Return: CF clear if successful
	CF set on error
	    AX = error code (see #01680 at AH=59h/BX=0000h)
Desc:	adjust the size of the per-process open file table, thus raising or
	  lowering the limit on the number of files the caller can open
	  simultaneously
Notes:	if BX <= 20, no action is taken if the handle limit has not yet been
	  increased, and the table is copied back into the PSP if the limit
	  is currently > 20 handles
	for file handle tables of > 20 handles, DOS 3.30 never reuses the
	  same memory block, even if the limit is being reduced; this can lead
	  to memory fragmentation as a new block is allocated and the existing
	  one freed
	only the first 20 handles are copied to child processes in DOS 3.3-6.0
	increasing the file handles here will not, in general, increase the
	  number of files that can be opened using the runtime library of a
	  high-level language such as C
	Novell DOS 7 reportedly terminates the calling program if the JFT is
	  being reduced in size and there are any open file handles beyond
	  the portion of the JFT being retained
BUGS:	the original release of DOS 3.30 allocates a full 64K for the handle
	  table on requests for an even number of handles
	DR DOS 3.41 and 5.0 will lose track of any open file handles beyond
	  the portion of the JFT retained after the call; MS-DOS will indicate
	  error 04h if any of the JFT entries to be removed are open
SeeAlso: AH=26h,AH=86h

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  Copyright 2000   by Ralf Brown     Updated Jul 2000