Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!husc6!lloyd!kent
From: kent@lloyd.camex.uucp (Kent Borg)
Newsgroups: comp.sys.mac.programmer
Subject: Re: what the heck is "reentrant"?
Keywords: reentrant
Message-ID: <105@lloyd.camex.uucp>
Date: 1 Aug 88 22:01:29 GMT
References: <730049@hpcilzb.HP.COM>
Reply-To: kent@lloyd.UUCP (Kent Borg)
Organization: Camex, Inc., Boston, Mass USA
Lines: 25

Reentrant means the code can be reentered.  In other words, if a
subroutine is reentrant, then many different programs can use the
subroutine (function, procedure, etc.) at the same time without
interfering with each other.  The main concern is that variables from
one instance of the routine does not interfear with another instance.

Because there is no preemptive multitasking in the Mac, programs don't
have to worry about other applications running behind their backs.
But they DO have to wonder whether some evil VBI task is doing things
it shouldn't, they have to coexist with desk accesories, and other
applications that might be running under MultiFinder.

There is another concrete reentrancy concern in the current Macintosh
community: There could be an application on an AppleShare volume that
is accessed by several Macintoshes.  For this to work, AppleShare must
allow it (I think there is a bit somewhere...), and the application
must be reentrant.  For example, temporary data must be distinct: if
you choose Undo, someone else's text should not appear in your
document.  The application also should not modify any of it's
resources, for example, preferences should be stored in separate file,
with a name/location that will not interfere with other user's
instances.

Kent Borg
kent@lloyd.uucp
or
husc6!lloyd!kent