Dealloc problem with SPMovieClip

membersheep

I noticed some memory leaks in the app I'm working on and I found the source of those problems in the SPMovieClips.
Basically when [clip play] is called from a touch event listener the clip won't be deallocated. Here's the example code to put in the barebone project. Just put a breakpoint in the dealloc implementation of the SPMovieClip class and try commenting and uncommenting the [clip play] in the init (when is commented touch near the top left corner of the screen to trigger the clip).
I never noticed this problem until now but it's clear it's causing many leaks in my app.
Here's the example code:

#import "Game.h"

@implementation Game

- (id)init
{
    if ((self = [super init]))
    {
        SPMovieClip *clip = [[SPMovieClip alloc]initWithFrame:[SPTexture textureWithContentsOfFile:@"Default.png"] fps:2];
        clip.name = @"clip";
// [clip addFrameWithTexture:[SPTexture textureWithContentsOfFile:@"frame1.png"]];
        [self addChild:clip];
        [[Sparrow juggler] addObject:clip];
        [clip stop];
// [clip play];
        [clip addEventListener:@selector(onTouch:)
                      atObject:self
                       forType:SP_EVENT_TYPE_TOUCH];
        [clip addEventListener:@selector(onComplete:)
                      atObject:self
                       forType:SP_EVENT_TYPE_COMPLETED];
    }
    return self;
}

- (void)onTouch:(SPEvent*)event
{
    SPMovieClip *clip = (SPMovieClip *)[self childByName:@"clip"];
    [clip play];
}

- (void)onComplete:(SPEvent*)event
{
    SPMovieClip *clip = (SPMovieClip *)[self childByName:@"clip"];
    [clip removeEventListener:@selector(onTouch:)
                     atObject:self
                      forType:SP_EVENT_TYPE_TOUCH];
    [clip removeEventListener:@selector(onComplete:)
                     atObject:self
                      forType:SP_EVENT_TYPE_COMPLETED];
    [self removeChild:clip];
    [[Sparrow juggler] removeObject:clip];
}

@end

Does anyone know what I'm doing wrong?
How do you start a clip by touching it?

Shilo

This is a nice catch! It could be possible that this bug existed in Sparrow before the change to ARC. I can't figure out the solution, but it seems the problem is related to the touch handling and SPTouch retaining the movieclip as the target.

Possible touch events that actually cause a dealloc:

Slow touch down and touch up
Touch down and move
Touch down twice

I believe the touches remain retained until the next set of touches are processed, which also means the target of the touches will remain retained. I am really rusty with MRC, so I can't even imagine a way to implement SPTouch's target property while keeping a weak instance.

I can only think of a workaround for this scenario:

@interface SPTouch (Internal)
- (void)setTarget:(SPDisplayObject *)target;
@end

...

//Release the target for all the touches
for (SPTouch *touch in event.touches) {
    [touch setTarget:nil];
}

Full code:

#import "Game.h"

@interface SPTouch (Internal)

- (void)setTarget:(SPDisplayObject *)target;

@end

@implementation Game {
    SPMovieClip *_clip;
}

- (id)init
{
    if ((self = [super init]))
    {
        _clip = [[SPMovieClip alloc]initWithFrame:[SPTexture textureWithContentsOfFile:@"Default.png"] fps:2];
        [self addChild:_clip];
        [_clip stop];
        [[Sparrow juggler] addObject:_clip];
        [_clip addEventListener:@selector(onTouch:)
                       atObject:self
                        forType:SP_EVENT_TYPE_TOUCH];
        [_clip addEventListener:@selector(onComplete:)
                          atObject:self
                           forType:SP_EVENT_TYPE_COMPLETED];
    }
    return self;
}

- (void)onTouch:(SPTouchEvent*)event
{
    [_clip play];

    //Release the target for all the touches
    for (SPTouch *touch in event.touches) {
        [touch setTarget:nil];
    }
}

- (void)onComplete:(SPEvent*)event
{
    [self removeChild:_clip];
    [[Sparrow juggler] removeObject:_clip];
    _clip = nil;
}

@end

Of course, you wouldn't want to do this for any other scenario. Again, my MRC knowledge is very rusty, so I could be overlooking the obvious.

Hopefully someone (Daniel) can shed some light on this.

membersheep

Thank you for your analysis I will try this asap on my test project. 🙂

Daniel

I just had a look at it, and actually I don't think it's that much of a problem.

You're right, when you add the breakpoint in "dealloc", it won't fire when the movie clip has finished playing, as you'd expect. However, just touch the screen a second time, and you'll see that the movie clip will be deallocated!

As Shilo correctly pointed out, the reason for this behavior is that the touch instance stores a reference to the movie clip. As you know, an "SPTouch" goes through a life cycle of "began - (moved) - ended". When you touch the screen a second time, "SPTouchProcessor" will notice that the previous touch has ended and will release the touch — and, at the same time, the movie clip.

So you won't lose any memory, it's just released a little later than one would expect.

The main issue is probably that "Instruments" won't be smart enough to understand that behavior, so you'll have lots of leak reports that are actually not a problem. But I can't think of an alternative solution, either: the touch instance must store (and retain) a reference to the target. If it didn't retain it, the code might run into a much severe problem: using an invalid pointer.

membersheep

Yeah I just tested it and it works exactly as you said, it's not a big deal since kids (main users of our apps) tend to touch the screen 100 times per second... 😃

Daniel

LOL! Good point. 🤣

Shilo

@Daniel
That's a good point. I was simply thinking of a "solution", but never wondered if it was really a "problem". Unless it is a very heavy movieclip, having the dealloc delayed by one touch isn't a big deal, as you pointed out. But it's also interesting that ARC can change the behavior of an app.

@membersheep
Those pesky 100TPS kids!

membersheep

Thank you for your answers.