Path: utzoo!utgpu!watserv1!watmath!att!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ira.uka.de!smurf!urlichs
From: urlichs@smurf.sub.org (Matthias Urlichs)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Non-Blocking io (stdin & MacTCP)
Keywords: async asynchronous KillIO PBKillIO
Message-ID: <4ab6g2.zc7@smurf.sub.org>
Date: 6 Nov 90 19:34:59 GMT
References: <520@mermaid.Litle.Com> <1990Nov2.194118.29698@hellgate.utah.edu> <16205@netcom.UUCP>
Organization: University of Karlsruhe, FRG
Lines: 32

In comp.sys.mac.programmer, article <16205@netcom.UUCP>,
  chrisj@netcom.UUCP (Christopher T. Jewell) writes:
< In article <1990Nov2.194118.29698@hellgate.utah.edu> u-lchoqu%peruvian.utah.edu@cs.utah.edu (Lee Choquette) writes:
< >On the Mac
< >you have a pending I/O request, and I can't find in Inside Mac a safe
< >way to cancel that request.  Does anyone out there know how to cancel
< >an asynchronous File Manager request?  What happens if your
< >application quits before the request completes?
< 
< On the Mac, asynchronous requests really only make sense with devices,
< not with files.

Why not ?

With floppy disks or AppleShare this makes perfect sense if you're willing to
add a little bit of complexity to your program (i.e. let the user continue to
look at his/her menus while your big file finishes loading).
I admit that it doesn't make sense with SCSI disks, but only because the
underlying block-level driver can't support async requests -- the MacOS SCSI
"Manager" sees to that. :-( :-(

The reason why you can't abort file manager requests is probably that it
won't make much sense. What is the result of aborting a PBDelete()? You only
delete half of the file? ;-)
Seriously, the internal complexity of the file manager is amazing (at least
from the point of view of someone who doesn't have access to the source code)
and it seems that the almost-never-needed ability to cancel requests would
have added yet another layer of complexity, and of bugs.

-- 
Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de     /(o\
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330)   \o)/