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From: fry@huma1.HARVARD.EDU (David Fry)
Newsgroups: comp.sys.mac
Subject: Re: When to HLock
Message-ID: <2961@husc6.UUCP>
Date: Thu, 8-Oct-87 11:41:32 EDT
Article-I.D.: husc6.2961
Posted: Thu Oct  8 11:41:32 1987
Date-Received: Sun, 11-Oct-87 01:48:36 EDT
References: <960@mntgfx.MENTOR.COM>
Sender: news@husc6.UUCP
Reply-To: fry@huma1.UUCP (David Fry)
Organization: Harvard Math Department
Lines: 30

In article <960@mntgfx.MENTOR.COM> tomc@mntgfx.MENTOR.COM (Tom Carstensen) writes:
>Question: Do you need to HLock in the following
>kind of situation?:
>
>TEHandle TheText;
>lines = (**TheText).nLines

No, because you're only accessing memory and assigning it to a
stack variable, lines.  You need to HLock when memory may be
moved.  Inside Mac has a list of Toolbox calls that can move
memory, but if you don't want to look it up you can call HLock
before a Toolbox routine (better to look it up).

Suppose, however that you wanted to create a NewWindow and the
refcon was going to be the number of lines in the TEHandle,
then you must HLock before calling the NewWindow because
NewWindow may move memory:

MoveHHi(TheText);
HLock(TheText);
myWindow = NewWindow( , ,...,(**TheText).nLines );
HUnlock(TheText);

"How to Write Macintosh Software" by Scott Kastner (sp?) is
a great source for tidbits like this.

David Fry				fry@huma1.harvard.EDU
Department of Mathematics		fry@harvma1.bitnet
Harvard University			...!harvard!huma1!fry
Cambridge, MA  02138