Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[じょいすじょん]

> On 2016 Dec 7, at 6:27, Carl Hoefs  wrote:
> 
>> 
>> On Dec 6, 2016, at 1:33 PM, Carl Hoefs  
>> wrote:
>> 
>>> On Dec 6, 2016, at 1:24 PM, David Duncan  wrote:
>>> 
>>> Your safest bets are to either clear the delegate of the layer at an 
>>> appropriate time (possibly in your view controller’s dealloc is all that is 
>>> necessary), or to use a UIView instead of a raw CALayer in this case. 
>>> Removing the layer would also suffice, as that would prevent UIKit from 
>>> seeing it at the time in question. Making the layer weak is probably 
>>> causing your reference to deallocate before it can be added to the layer 
>>> tree, which is why it doesn’t display in that case.
>> 
>> Thanks for this explanation, David! 
>> 
>> I've verified that using either of:
>>   [self.layer setDelegate:nil];
>> or
>>   [self.layer removeFromSuperlayer];
>> will prevent the crash. 
> 
> Followup: It turns out that the 'offending' line of code is:
> 
>  [self.layer setDelegate:self];
> 
> If I don't set this, everything still works correctly, and there's no crash 
> at dealloc time.
> 
> -Carl
> 
That sure looks like a circle until you remove something :)
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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[Carl Hoefs]

> On Dec 6, 2016, at 1:33 PM, Carl Hoefs  wrote:
> 
>> On Dec 6, 2016, at 1:24 PM, David Duncan  wrote:
>> 
>> Your safest bets are to either clear the delegate of the layer at an 
>> appropriate time (possibly in your view controller’s dealloc is all that is 
>> necessary), or to use a UIView instead of a raw CALayer in this case. 
>> Removing the layer would also suffice, as that would prevent UIKit from 
>> seeing it at the time in question. Making the layer weak is probably causing 
>> your reference to deallocate before it can be added to the layer tree, which 
>> is why it doesn’t display in that case.
> 
> Thanks for this explanation, David! 
> 
> I've verified that using either of:
>[self.layer setDelegate:nil];
> or
>[self.layer removeFromSuperlayer];
> will prevent the crash. 

Followup: It turns out that the 'offending' line of code is:

  [self.layer setDelegate:self];

If I don't set this, everything still works correctly, and there's no crash at 
dealloc time.

-Carl


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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[Carl Hoefs]

> On Dec 6, 2016, at 1:24 PM, David Duncan  wrote:
> 
> Your safest bets are to either clear the delegate of the layer at an 
> appropriate time (possibly in your view controller’s dealloc is all that is 
> necessary), or to use a UIView instead of a raw CALayer in this case. 
> Removing the layer would also suffice, as that would prevent UIKit from 
> seeing it at the time in question. Making the layer weak is probably causing 
> your reference to deallocate before it can be added to the layer tree, which 
> is why it doesn’t display in that case.

Thanks for this explanation, David! 

I've verified that using either of:
[self.layer setDelegate:nil];
or
[self.layer removeFromSuperlayer];
will prevent the crash. It's just a bit
surprising to me that this is needed...

-Carl


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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[David Duncan]

> On Dec 6, 2016, at 11:51 AM, Doug Hill  wrote:
> 
> I've wondered about this before, but maybe some Objective-C runtime experts 
> know.
> 
> Does writing directly to the ivar backing a property bypass the ARC features 
> of the property. For example, will a strong property be retained if you write 
> directly to the ivar?

Yes, under ARC assigning to a strong ivar and assigning via a strong property 
are identical with respect to the resulting retain count semantics (otherwise 
typically constructed ARC-based setter methods wouldn’t work).

> 
> If not, that's your problem.
> 
> Doug
> 
>> On Dec 6, 2016, at 11:44 AM, Carl Hoefs > > wrote:
>> 
>> I get the following crash in my iOS 9 app simply by adding a CALayer to the 
>> current view controller's self.view.layer and then dismissing the current 
>> view controller. Simplified code:
>> 
>>   @property (strong,nonatomic) CALayer *layer;
>>   .  .  .
>>   _layer = [[CALayer alloc] init];
>>   [_layer setDelegate: self];
>>   [self.view.layer addSublayer:_layer];
>> 
>> Upon dismissing the VC:
>> 
>>   [self dismissViewControllerAnimated:YES completion:nil];
>> 
>> The following exception occurs:
>> 
>> (lldb) bt
>> * thread #1: tid = 0x121bd, 0x22c2c68a libobjc.A.dylib`objc_retain + 10, 
>> queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
>> address=0xb010)
>>   frame #0: 0x22c2c68a libobjc.A.dylib`objc_retain + 10
>>   frame #1: 0x27a2a22a UIKit`-[UIView(Hierarchy) subviews] + 330
>>   frame #2: 0x27b3e1ea UIKit`discardEngineRecursive + 118
>>   frame #3: 0x27a2fd06 UIKit`-[UIView dealloc] + 630
>>   frame #4: 0x2336cd98 CoreFoundation`-[__NSDictionaryM dealloc] + 132
>>   frame #5: 0x22c2cf8a libobjc.A.dylib`objc_object::sidetable_release(bool) 
>> + 150
>>   frame #6: 0x22c2d3cc libobjc.A.dylib`(anonymous 
>> namespace)::AutoreleasePoolPage::pop(void*) + 388
>>   frame #7: 0x23363f30 CoreFoundation`_CFAutoreleasePoolPop + 16
>>   frame #8: 0x23415c56 CoreFoundation`__CFRunLoopRun + 1598
>>   frame #9: 0x233641c8 CoreFoundation`CFRunLoopRunSpecific + 516
>>   frame #10: 0x23363fbc CoreFoundation`CFRunLoopRunInMode + 108
>>   frame #11: 0x24980af8 GraphicsServices`GSEventRunModal + 160
>>   frame #12: 0x27a9c434 UIKit`UIApplicationMain + 144
>> * frame #13: 0x001b655e ProteinFold`main(argc=1, argv=0x0043bbc8) + 122 at 
>> main.m:14
>> 
>> If I remove the CALayer first before the 
>> -dismissViewControllerAnimated:completion:, it doesn't crash:
>> 
>>   [layer removeFromSuperlayer];
>> 
>> Why do I need to explicitly remove my added CALayer before dismissing the 
>> VC? Note: If I declare layer as weak, the crash does not occur, but neither 
>> does the layer display onscreen.
>> -Carl
>> 
>> 
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> 
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--
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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[David Duncan]

> On Dec 6, 2016, at 11:44 AM, Carl Hoefs  
> wrote:
> 
> I get the following crash in my iOS 9 app simply by adding a CALayer to the 
> current view controller's self.view.layer and then dismissing the current 
> view controller. Simplified code:
> 
>@property (strong,nonatomic) CALayer *layer;
>.  .  .
>_layer = [[CALayer alloc] init];
>[_layer setDelegate: self];
>[self.view.layer addSublayer:_layer];
> 
> Upon dismissing the VC:
> 
>[self dismissViewControllerAnimated:YES completion:nil];
> 
> The following exception occurs:
> 
> (lldb) bt
> * thread #1: tid = 0x121bd, 0x22c2c68a libobjc.A.dylib`objc_retain + 10, 
> queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
> address=0xb010)
>frame #0: 0x22c2c68a libobjc.A.dylib`objc_retain + 10
>frame #1: 0x27a2a22a UIKit`-[UIView(Hierarchy) subviews] + 330
>frame #2: 0x27b3e1ea UIKit`discardEngineRecursive + 118
>frame #3: 0x27a2fd06 UIKit`-[UIView dealloc] + 630
>frame #4: 0x2336cd98 CoreFoundation`-[__NSDictionaryM dealloc] + 132
>frame #5: 0x22c2cf8a libobjc.A.dylib`objc_object::sidetable_release(bool) 
> + 150
>frame #6: 0x22c2d3cc libobjc.A.dylib`(anonymous 
> namespace)::AutoreleasePoolPage::pop(void*) + 388
>frame #7: 0x23363f30 CoreFoundation`_CFAutoreleasePoolPop + 16
>frame #8: 0x23415c56 CoreFoundation`__CFRunLoopRun + 1598
>frame #9: 0x233641c8 CoreFoundation`CFRunLoopRunSpecific + 516
>frame #10: 0x23363fbc CoreFoundation`CFRunLoopRunInMode + 108
>frame #11: 0x24980af8 GraphicsServices`GSEventRunModal + 160
>frame #12: 0x27a9c434 UIKit`UIApplicationMain + 144
>  * frame #13: 0x001b655e ProteinFold`main(argc=1, argv=0x0043bbc8) + 122 at 
> main.m:14

This is due to the confluence of a few UIKit implementation details. The bottom 
line is that UIKit is trying to iterate the subviews of your view controller’s 
view, encounters your layer, and tries to retain the layer’s delegate. Because 
the layer’s delegate is assign (not weak) and the view controller has already 
been deallocated, this explodes taking your app with it.

Your safest bets are to either clear the delegate of the layer at an 
appropriate time (possibly in your view controller’s dealloc is all that is 
necessary), or to use a UIView instead of a raw CALayer in this case. Removing 
the layer would also suffice, as that would prevent UIKit from seeing it at the 
time in question. Making the layer weak is probably causing your reference to 
deallocate before it can be added to the layer tree, which is why it doesn’t 
display in that case.

> 
> If I remove the CALayer first before the 
> -dismissViewControllerAnimated:completion:, it doesn't crash:
> 
>[layer removeFromSuperlayer];
> 
> Why do I need to explicitly remove my added CALayer before dismissing the VC? 
> Note: If I declare layer as weak, the crash does not occur, but neither does 
> the layer display onscreen.
> -Carl
> 
> 
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--
David Duncan


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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[Carl Hoefs]

FWIW, it still crashes if I change the code to use self.layer instead of _layer:

   @property (strong,nonatomic) CALayer *layer;
   .  .  .
   self.layer = [[CALayer alloc] init];
   [self.layer setDelegate: self];
   [self.view.layer addSublayer:self.layer];

-Carl

> On Dec 6, 2016, at 12:51 PM, Doug Hill  wrote:
> 
> I've wondered about this before, but maybe some Objective-C runtime experts 
> know.
> 
> Does writing directly to the ivar backing a property bypass the ARC features 
> of the property. For example, will a strong property be retained if you write 
> directly to the ivar?
> 
> If not, that's your problem.
> 
> Doug
> 
>> On Dec 6, 2016, at 11:44 AM, Carl Hoefs  
>> wrote:
>> 
>> I get the following crash in my iOS 9 app simply by adding a CALayer to the 
>> current view controller's self.view.layer and then dismissing the current 
>> view controller. Simplified code:
>> 
>>   @property (strong,nonatomic) CALayer *layer;
>>   .  .  .
>>   _layer = [[CALayer alloc] init];
>>   [_layer setDelegate: self];
>>   [self.view.layer addSublayer:_layer];
>> 
>> Upon dismissing the VC:
>> 
>>   [self dismissViewControllerAnimated:YES completion:nil];
>> 
>> The following exception occurs:
>> 
>> (lldb) bt
>> * thread #1: tid = 0x121bd, 0x22c2c68a libobjc.A.dylib`objc_retain + 10, 
>> queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
>> address=0xb010)
>>   frame #0: 0x22c2c68a libobjc.A.dylib`objc_retain + 10
>>   frame #1: 0x27a2a22a UIKit`-[UIView(Hierarchy) subviews] + 330
>>   frame #2: 0x27b3e1ea UIKit`discardEngineRecursive + 118
>>   frame #3: 0x27a2fd06 UIKit`-[UIView dealloc] + 630
>>   frame #4: 0x2336cd98 CoreFoundation`-[__NSDictionaryM dealloc] + 132
>>   frame #5: 0x22c2cf8a libobjc.A.dylib`objc_object::sidetable_release(bool) 
>> + 150
>>   frame #6: 0x22c2d3cc libobjc.A.dylib`(anonymous 
>> namespace)::AutoreleasePoolPage::pop(void*) + 388
>>   frame #7: 0x23363f30 CoreFoundation`_CFAutoreleasePoolPop + 16
>>   frame #8: 0x23415c56 CoreFoundation`__CFRunLoopRun + 1598
>>   frame #9: 0x233641c8 CoreFoundation`CFRunLoopRunSpecific + 516
>>   frame #10: 0x23363fbc CoreFoundation`CFRunLoopRunInMode + 108
>>   frame #11: 0x24980af8 GraphicsServices`GSEventRunModal + 160
>>   frame #12: 0x27a9c434 UIKit`UIApplicationMain + 144
>> * frame #13: 0x001b655e ProteinFold`main(argc=1, argv=0x0043bbc8) + 122 at 
>> main.m:14
>> 
>> If I remove the CALayer first before the 
>> -dismissViewControllerAnimated:completion:, it doesn't crash:
>> 
>>   [layer removeFromSuperlayer];
>> 
>> Why do I need to explicitly remove my added CALayer before dismissing the 
>> VC? Note: If I declare layer as weak, the crash does not occur, but neither 
>> does the layer display onscreen.
>> -Carl
>> 
>> 
>> ___
>> 
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>> 
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> 


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Re: iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[Doug Hill]

I've wondered about this before, but maybe some Objective-C runtime experts 
know.

Does writing directly to the ivar backing a property bypass the ARC features of 
the property. For example, will a strong property be retained if you write 
directly to the ivar?

If not, that's your problem.

Doug

> On Dec 6, 2016, at 11:44 AM, Carl Hoefs  
> wrote:
> 
> I get the following crash in my iOS 9 app simply by adding a CALayer to the 
> current view controller's self.view.layer and then dismissing the current 
> view controller. Simplified code:
> 
>@property (strong,nonatomic) CALayer *layer;
>.  .  .
>_layer = [[CALayer alloc] init];
>[_layer setDelegate: self];
>[self.view.layer addSublayer:_layer];
> 
> Upon dismissing the VC:
> 
>[self dismissViewControllerAnimated:YES completion:nil];
> 
> The following exception occurs:
> 
> (lldb) bt
> * thread #1: tid = 0x121bd, 0x22c2c68a libobjc.A.dylib`objc_retain + 10, 
> queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
> address=0xb010)
>frame #0: 0x22c2c68a libobjc.A.dylib`objc_retain + 10
>frame #1: 0x27a2a22a UIKit`-[UIView(Hierarchy) subviews] + 330
>frame #2: 0x27b3e1ea UIKit`discardEngineRecursive + 118
>frame #3: 0x27a2fd06 UIKit`-[UIView dealloc] + 630
>frame #4: 0x2336cd98 CoreFoundation`-[__NSDictionaryM dealloc] + 132
>frame #5: 0x22c2cf8a libobjc.A.dylib`objc_object::sidetable_release(bool) 
> + 150
>frame #6: 0x22c2d3cc libobjc.A.dylib`(anonymous 
> namespace)::AutoreleasePoolPage::pop(void*) + 388
>frame #7: 0x23363f30 CoreFoundation`_CFAutoreleasePoolPop + 16
>frame #8: 0x23415c56 CoreFoundation`__CFRunLoopRun + 1598
>frame #9: 0x233641c8 CoreFoundation`CFRunLoopRunSpecific + 516
>frame #10: 0x23363fbc CoreFoundation`CFRunLoopRunInMode + 108
>frame #11: 0x24980af8 GraphicsServices`GSEventRunModal + 160
>frame #12: 0x27a9c434 UIKit`UIApplicationMain + 144
>  * frame #13: 0x001b655e ProteinFold`main(argc=1, argv=0x0043bbc8) + 122 at 
> main.m:14
> 
> If I remove the CALayer first before the 
> -dismissViewControllerAnimated:completion:, it doesn't crash:
> 
>[layer removeFromSuperlayer];
> 
> Why do I need to explicitly remove my added CALayer before dismissing the VC? 
> Note: If I declare layer as weak, the crash does not occur, but neither does 
> the layer display onscreen.
> -Carl
> 
> 
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iOS 9: Adding CALayer to self.view.layer causes EXC_BAD_ACCESS

[Carl Hoefs]

I get the following crash in my iOS 9 app simply by adding a CALayer to the 
current view controller's self.view.layer and then dismissing the current view 
controller. Simplified code:

@property (strong,nonatomic) CALayer *layer;
.  .  .
_layer = [[CALayer alloc] init];
[_layer setDelegate: self];
[self.view.layer addSublayer:_layer];

Upon dismissing the VC:

[self dismissViewControllerAnimated:YES completion:nil];

The following exception occurs:

(lldb) bt
* thread #1: tid = 0x121bd, 0x22c2c68a libobjc.A.dylib`objc_retain + 10, queue 
= 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, 
address=0xb010)
frame #0: 0x22c2c68a libobjc.A.dylib`objc_retain + 10
frame #1: 0x27a2a22a UIKit`-[UIView(Hierarchy) subviews] + 330
frame #2: 0x27b3e1ea UIKit`discardEngineRecursive + 118
frame #3: 0x27a2fd06 UIKit`-[UIView dealloc] + 630
frame #4: 0x2336cd98 CoreFoundation`-[__NSDictionaryM dealloc] + 132
frame #5: 0x22c2cf8a libobjc.A.dylib`objc_object::sidetable_release(bool) + 
150
frame #6: 0x22c2d3cc libobjc.A.dylib`(anonymous 
namespace)::AutoreleasePoolPage::pop(void*) + 388
frame #7: 0x23363f30 CoreFoundation`_CFAutoreleasePoolPop + 16
frame #8: 0x23415c56 CoreFoundation`__CFRunLoopRun + 1598
frame #9: 0x233641c8 CoreFoundation`CFRunLoopRunSpecific + 516
frame #10: 0x23363fbc CoreFoundation`CFRunLoopRunInMode + 108
frame #11: 0x24980af8 GraphicsServices`GSEventRunModal + 160
frame #12: 0x27a9c434 UIKit`UIApplicationMain + 144
  * frame #13: 0x001b655e ProteinFold`main(argc=1, argv=0x0043bbc8) + 122 at 
main.m:14

If I remove the CALayer first before the 
-dismissViewControllerAnimated:completion:, it doesn't crash:

[layer removeFromSuperlayer];

Why do I need to explicitly remove my added CALayer before dismissing the VC? 
Note: If I declare layer as weak, the crash does not occur, but neither does 
the layer display onscreen.
-Carl


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