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From: olson@bootsie.uucp (Eric K. Olson)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Is this possible with the Resource Manager?
Message-ID: <1991Feb20.101151.22358@bootsie.uucp>
Date: 20 Feb 91 10:11:51 GMT
References: <1CE00001.ed5n0r@tbomb.ice.com> <12158@goofy.Apple.COM>
Organization: Lexington Software Design, Lexington, MA
Lines: 85

In a recent article, Larry Rosenstein (lsr@Apple.COM) writes:
>[Re: Reading data from disk while resource in memory]
>
> You have to do this without calling DetachResource.
> One way that comes to mind is:
> 
>if (*resHand != NULL) {
> 		/* save current contents */
> 	oldSize = GetHandleSize(resHand);
> 	save = NewHandle(oldSize);
> 	BlockMove(*resHand, *save, oldSize);
> 
> 	EmptyHandle(resHand);
> 	LoadResource(resHand);	/* re-load disk copy */
> 
> 	diskCopy = resHand;
> 	HandToHand(diskCopy);	/* make a copy of it */
	           ^^^^^^^^
	HandToHand(&diskCopy);

> 
> 		/* restore original version */
> 	SetHandleSize(resHand, oldSize);
> 	BlockMove(*save, *resHand, oldSize);
> 	DisposHandle(save);
> }
> 

This code is more like what I was looking for.  I definitely prefer this
to the rule-breaking solution I posted earlier.  I've tried it (with
the fix to HandToHand()) and it seems to work fine.

Thanks Again, Larry!

It's worth noting that in THINK C (and probably MPW), the call to
HandToHand() in the included code below should be:

	HandToHand(&diskCopy);

It occurs to me that calling DetachResource() on _any_ resource in the
currently running Application could be dangerous (if that resource has
been GetResource()'ed by some other part of your program).  It might
help to think of my application as a parasitic FKEY resource editor
(it's not-- it's the Prepare() View Editor) that can't really know what
resources are in use by the host application.  (Similarly, the View
Editor is intended to work compiled into any other application, whose
objects may be using resources).

Is it possible to know what resources have been gotten and have since
been purged? Or gotten with SetResLoad(FALSE)? You can't call
DetachResource() on those, either, I presume, although you can
HandToHand() it and return the copy, then EmptyHandle() the resource
handle if it was empty before.  Or I could call HPurge() on the
resource handle (if it was empty before), so it might remain
in memory until the next time it's GetResource()'ed.  Is this kosher?

/* Detach a resource, leaving previous references around */

Handle MyDetachResource(Handle aResHandle, Boolean wasLoaded)
{
	Handle		aDataHandle;
	
	aDataHandle = aResHandle;
	HandToHand(&aResHandle);
	if (!wasLoaded) {
		HPurge(aResHandle);    OR     EmptyHandle(aResHandle);
		}
	return aDataHandle;
	}
	

-Eric








-- 
Eric K. Olson, Editor, Prepare()      NOTE:     olson@bootsie.uucp doesn't work
Lexington Software Design             Internet: olson@endor.harvard.edu
72A Lowell St., Lexington, MA  02173  Uucp:     harvard!endor!olson
(617) 863-9624                        Bitnet:   OLSON@HARVARD