应用程序在iPad 2上工作正常，在iPad 3上崩溃，内存警告低

Question

as the title says, I have an app which works on iPad 2, but crashes on iPad 3. when running it the console gives me a low memory warning message. When the crash happens I symbolicate it, but there's really nothing that I can relate to the code, like it shows

   process name, UUID, rpages, recent_max, [reason] (state)

and under those column headers just hexadecimal stuff, nothing showing method calls or lines in the project.

Any ideas? am I missing some flags in the code that allows for a better crash log?

Thanks.

Answer 1

If you're getting low memory warnings and fail to release enough memory to resolve the issue, your app will almost certainly crash. The thing is, I don't think that the particulars of how or why it crashed can possibly be illuminating. At that point, you're evaluating secondary symptoms. You really need to go back and figure out why you got the low memory warning in the first place and fix that problem.

As Daniel said, you can look at Technical Note 2151 , but as it says:

When you see a low memory crash, rather than be concerned about what part of your code was executing at the time of termination, you should investigate your memory usage patterns and your responses to low memory warnings. Memory Allocations Help lists detailed steps on how to use the Leaks Instrument to discover memory leaks, and how to use the Allocations Instrument's Mark Heap feature to avoid abandoned memory. Memory Usage Performance Guidelines discusses the proper ways to respond to low-memory notifications as well as many tips for using memory effectively. It is also recommended that you check out the WWDC 2010 session, Advanced Memory Analysis with Instruments .

So, a couple of thoughts:

1. Have you looked for leaks? The Finding Leaks article walks you through how to use instruments to find your leaks.

2. If you turned on zombies, have you turned them off? Zombies is a great diagnostic tool, but just consumes memory.

3. Have you run your code through the static analyzer ( shift + command + B or select "Analyze" on the "Product" menu)? Especially if using non-ARC code, this can find lots of memory issues.

4. Have you examined your allocations for unexplained increases without offsetting decreases with the Instrument's Allocations tool. Using that, you can run the program, look at the consumption of memory on the graph and see if you see any increases that aren't offset at some point by the corresponding decreases. And if so, highlight those increases in the graph:

   For example, when running the Allocations tool, hold down the option key and then click-and-drag with your mouse to highlight a portion of the timeline, to identify what you want to inspect. You probably want to focus on one of your spikes in allocations. For example, I found a bump in my allocations and highlighted it as such (this was a ludicrously simple example where I create a huge array in viewDidLoad , but hopefully it give you the idea):

   

   Note, I find it useful to show the call tree in the lower panel, it's often useful to select "Hide System Libraries", to focus on your code (and "Invert Call Tree", too). And if you double click on the method name in Instruments (in my example, here, it would be viewDidLoad), Instruments will then show you your code that's doing the allocation:

   

Answer 2

Low memory warnings generate a different kind of log than standard crashes. Take a look at the "Understanding Low Memory Reports" section of this article to understand what happened with your application and how you can debug it using Instruments: http://developer.apple.com/library/ios/#technotes/tn2151/_index.html