Malloc Crash when creating UIImage?

Question

I know its a little bit general , but we did EVERY possible thing to find what it is, and we just couldn't .

We have this crash that happens here and there, not always, on this line :

[self.imageOperationQueue addOperationWithBlock:^
 {
    if(!data)
        return ;
    UIImage *image=[[UIImage alloc] initWithData:data]; // *** CRASH !

The crash log says :

malloc: *** error for object 0x7fecdb06e5c0: double free
*** set a breakpoint in malloc_error_break to debug

As you can see, and upon our check , data is not nil when we are creating the image , we have also tried with : [UIImage initWithData:data]; without allocation , but same thing.

EDIT: this is how the code looks like after this row :

       if(!data)
          return ;


      UIImage *image=[[UIImage alloc] initWithData:data];
      UIImageView *modelview=[self.allImageView objectAtIndex:index];
      float newH=image.size.height* (1.65*modelview.frame.size.width/image.size.width);
      CGSize s=CGSizeMake(1.65*modelview.frame.size.width, newH);

      if (image)
      {
          UIGraphicsBeginImageContextWithOptions(s , NO, 0.0);
          [image drawInRect:CGRectMake(0, 0, s.width, s.height)];

          image = UIGraphicsGetImageFromCurrentImageContext();
          UIGraphicsEndImageContext();
      }

Yes, set a breakpoint in malloc_error_break to debug and enable zombies — Lefteris, Nov 06 '14 at 10:24
http://stackoverflow.com/questions/10587266/double-free-set-a-breakpoint-in-malloc-error-break-to-debug-in-arc go through this link. — , Nov 06 '14 at 11:03
why not simply [[UIImage alloc] initWithData:data.copy] and see how it goes — Nicolas Manzini, Nov 06 '14 at 13:00
http://stackoverflow.com/questions/10587266/double-free-set-a-breakpoint-in-malloc-error-break-to-debug-in-arc?lq=1 — Nicolas Manzini, Nov 06 '14 at 13:01
I got this crash when the disk is full. Don't know how to solve it yet. — Jaybo, Jan 07 '17 at 06:08

score 3 · Answer 1 · answered Nov 06 '14 at 10:52

3

Your data is likely being over-released on another thread. The double-free indicates a memory management imbalance, not a nil-pointer.

If I had to predict the problem, I'd guess you're generating data from an unsafe pointer, maybe the result of a CoreGraphics call, or a NSData over malloc'ed memory that gets freed behind your back. Here's how my theory works:

You create the NSData over unsafe memory
You create this operation block, which puts a retain on the NSData
Somewhere else, you free the underlying memory
The operation block runs
This is the last line that uses data
ARC notices that and so releases data at the semicolon
Releasing data leads to a free()
Memory was already freed by someone else
Crash

The key is that NSData typically should be the sole owner of its memory; if it's not, then you have to be very careful, especially in multi-threaded operations.

answered Nov 06 '14 at 10:52

Rob Napier

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thanks-Please check my edit : you right i do use core graphic right after that, but the crash shows that its that line . So , bottom line how would i change this code to stop this from happen ? every time i want to load 4 next images from a server i use this block( a regular lazy loading) – Curnelious Nov 06 '14 at 12:50
1

@Curnelious - By the time you get to the failing line it's too late. – Hot Licks Nov 06 '14 at 12:53
The bug probably isn't here. It's probably in the code that generates data and then calls this. – Rob Napier Nov 07 '14 at 14:39

Malloc Crash when creating UIImage?

1 Answers1