Re: [xmlvm-users] Mixing GC code with Objective-C code

[Steve H. <st...@we...>]

Thanks for the reply, Arno.  The paper you sent me was quite helpful
on this subject also.  Both here, and in the paper, you talk about
wrapping Objective-C objects with GC managed objects.  I'm curious
about the inverse situation, where you are wrapping GC managed objects
with Objective-C objects.

E.g. consider this class definition:

//
//  ViewController.h
//  XcodeGUIApp
//
//  Created by Steve Hannah on 2013-02-20.
//  Copyright (c) 2013 Web Lite Solutions. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "xmlvm.h"

@interface NotesListController : UIViewController
<UITableViewDataSource, UITableViewDelegate>
@property (retain, nonatomic) IBOutlet UITableView *tableView;
@property JAVA_OBJECT notes;
-(void)refreshNotes;
-(void)viewDidAppear:(BOOL)animated;
-(void)tableView:(UITableView *)tableView
didSelectRowAtIndexPath:(NSIndexPath *)indexPath;
@end

(In particular, notice the
@property JAVA_OBJECT notes;
)

Then at some point the "notes" property is set like this:

self.notes = ca_weblite_crossmobile_shared_Note_getNotes__();

Do I need to do anything special to let the GC know that the
JAVA_OBJECT is being "used" in this structure?  I.e. is there a chance
that the GC will free the notes object while the Objective-C class
still needs it?

Thanks again for all your help.

-Steve




On Thu, Feb 21, 2013 at 10:30 PM, Arno Puder <ar...@pu...> wrote:
>
> this is an extremely tricky subject. Yes, you have to be very careful
> when mixing the two memory management models. I can only barely scratch
> the surface but, in essence, the cross-compiled Java version of NSObject
> becomes a wrapper around the native instance to an NSObject. When the GC
> reclaims the cross-compiled NSObject, it will call a finalizer
> (essentially overriding Object.finalize()) that will delegate the
> release to the wrapped Objective-C instance. But as I said, it gets a
> lot more complicated: associations between objects (e.g.
> UIView.subviews) and delegates need special attention.
>
> Arno
>
>
> On 2/21/13 7:49 PM, Steve Hannah wrote:
>> I'm experimenting using XMLVM to compile business logic, which I then
>> use inside a Cocoa GUI app - built with Xcode.  I am trying to get an
>> understanding of the implications of XMLVM's garbage collected
>> pointers used together with objective-c objects.
>>
>> This page <http://www.hpl.hp.com/personal/Hans_Boehm/gc/simple_example.html>
>> says:
>> "It is usually best not to mix garbage-collected allocation with the
>> system malloc-free. If you do, you need to be careful not to store
>> pointers to the garbage-collected heap in memory allocated with the
>> system malloc."
>>
>> Does this mean that I shouldn't be storing JAVA_OBJECTs as properties
>> of objective-c classes?  Are there any best practices that should be
>> followed here?
>>
>> Thanks for any tips.
>>
>> -Steve
>>
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>
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-- 
Steve Hannah
Web Lite Solutions Corp.