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From: 6500stom@hub.UUCP
Newsgroups: comp.sys.mac.programmer
Subject: Re: HLock
Message-ID: <3331@hub.UUCP>
Date: 16 Dec 89 06:59:47 GMT
Sender: news@hub.UUCP
Lines: 25

> I know this has been discussed before, but could someone tell me when
> it is necessary to use HLock?  If i have a handle within a CDEF do i need
> to do so?  What if i only access the handle thru a pointer, i.e. :
> 
> void doSomething(theControl)
> ControlHandle theControl;
> {
> ControlPtr cp;
> 
> cp = *theControl;
> if (cp->contrlRect ...... and so on.......

It doesn't matter whether you dereference it or not in C.  You might
as well have done (**theControl).contrlRect instead of cp->contrlRect.
The way to remember if you need to lock your handle is if you pass
a field in the handle to any procedure that might move memory--even
if its one of your own routines in a different segment.
For example, if you do
RectRgn(myRgn, (**theControl).contrlRect) you need to lock theControl
down because RectRgn might move the handle before its done with the
contrlRect.
/            Josh Pritikin             T Ignorance is bliss.           \
| Mail:      6500stom@ucsbuxa.ucsb.edu | I must be in hell.            |
| AppleLink: Josh.P                    | My room is proof that entropy |
\ GEnie:     J.Pritikin                ! exists.                       /