Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!cwjcc!gatech!rutgers!apple!bionet!agate!ucbvax!CORY.BERKELEY.EDU!dillon
From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Standardization
Message-ID: <8810260715.AA16093@cory.Berkeley.EDU>
Date: 26 Oct 88 07:15:53 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 35

:>	Just do an Examine, and compare the change data for the
:>directory with the old change date: if they're different, something may
:This would work fine, except WHEN do you check?  You certainly check

:pds@quintus.uucp Writes:
:...
:right away.  Does your program check the change date for the directory
:every few seconds just to see if something has changed?  Wouldn't this
:create a lot of useless disk accesses?


	Checking every couple of seconds while the requester is up would
work out just fine!  No disk accesses would occur under 'idle' operation
(nobody else doing major accesses to the disk) because the directory
block would be cached.
>Couldn't this be accomplished by putting a process in the "food chain"
>before the disk (and RAM:, RAD:, etc.)  devices that watch for file
:creation and deletion packets, and send the appropriate messages to any
:programs that are displaying info about that directory.  Can this be
:done?  This is something someone outside of DOGS could do (unlike
:changing the file system).  If done right, C= might "bless" it, and use
:it to keep Workbench windows up-to-date.

	Not really... it would be an incredible hack and take too much
overhead to be worth it for anybody but C-A to do it.  Reason: Each and 
every DOS device you see out there is its own process.  Sure you could 
re-vector the DOS library call for Open()  etc... but then what?

	It can be done, but would mean implementation of a new packet 
type associated with locks.  A "signal me if sub entries of this lock
are touched" Call.  If that *were* done, you might as well also implement
file-level exclusive/shared locks (ala UNIX flock() call)...  We're talking
very major addition here.

				-Matt