CODEWITHSUNDEEP
objective-ciossegmentation-fault
Joel Martinez
Joel Martinez

Reputation: 47759

Translating an iOS stack trace - SIGSEGV/SEGV_ACCERR on viewDidUnload

I'm guessing that this problem is a lifecycle problem. The app receives a memory warning and tries to unload some user interface items. But I'm not 100% sure how to interpret the error in the context of the last reported item on the stack trace.

Exception Type:  SIGSEGV
Exception Codes: SEGV_ACCERR at 0xa0d9f968
Crashed Thread:  0

Thread 0 Crashed:
0   libobjc.A.dylib                     0x361dc026 objc_msgSend_stret + 18
1   TheApp                              0x000b4d31 -**[TheAppFeedController removeAdView]** (TheAppFeedController.m:**189**)
2   TheApp                              0x0000d68d -[TheAppViewController viewDidUnload] (TheAppViewController.m:177)
3   TheApp                              0x000b4a63 -[TheAppFeedController viewDidUnload] (TheAppFeedController.m:137)
4   UIKit                               0x32e66a37 -[UIViewController unloadViewForced:] + 251
5   UIKit                               0x32fae3ad -[UIViewController purgeMemoryForReason:] + 65

So the stack trace points to this method which doesn't really make sense why it would throw this error.

-(void) removeAdView {
    [super removeAdView];
    [self fixLayoutForAdRemoval:self.tableView];
}

The one thing I did notice when you look up the stack is that [super viewDidUnload] was being called as the first line of code. So I moved it to the bottom, after I do all my "unloading" work. There seems to be some disagreement online whether this really matters or not, some SO answers say that the super class' viewDidUnload method does nothing, and as such it doesn't matter if you call it at the beginning or the end.

So I've made that change, but since I've never been able to reproduce this error I'm not sure if it's the actual fix. Wanted to get more opinions on the problem to see if my reasoning is correct.

Upvotes: 0

Views: 1872

Answers (1)

bbum
bbum

Reputation: 162712

[super removeAdView];
[self fixLayoutForAdRemoval:self.tableView];

If removeAdView is tearing down parts of self; if it is causing self to be released to the point of deallocation, then the subsequent call to fixLayoutForAdRemoval: could easily fail.

Turn on Zombie detection in Instruments and see what it detects.

Upvotes: 1

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