Category: <b>DOS kernel</b>
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<pre><b>INT 21 - DOS 3.0+ - "FLOCK" - RECORD LOCKING</b>

	AH = 5Ch
	AL = subfunction
	    00h lock region of file
	    01h unlock region of file
	BX = file handle
	CX:DX = start offset of region within file
	SI:DI = length of region in bytes
Return: CF clear if successful
	CF set on error
	    AX = error code (01h,06h,21h,24h) (see <a href=../../it/80/16.html>#01680</a>)
Notes:	error returned unless SHARE or network installed
	an unlock call must specify the same region as some prior lock call
	locked regions become entirely inaccessible to other processes
	duplicate handles created with AH=45h or AH=46h inherit locks, but
	  handles inherited by child processes (see AH=4Bh) do not
	under DR DOS 3.41 and 5.0, if a process opens a file without the no-
	  inherit flag and then starts a child, any locks set by the parent
	  are ignored, and the child will only get an error if it tries to
	  lock an area previously locked by the parent process.	 Under Novell
	  DOS 7, this function is fully supported as in MS-DOS.
SeeAlso: AX=440Bh,AH=BCh,AH=BEh,INT 2F/AX=110Ah,INT 2F/AX=110Bh
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