Intermittent memory leaks

Question

I am testing a particular use case for leaks. Sometimes, I get the leaks and other times I don't even if I go through the same usecase. Can you suggest whether it is because of the system frameworks or my code?

I have checked in my code and everthing looks perfect without any unreleased objects. Can you suggest a solution?

Thanks

Answer 1

The most likely source for an intermittent memory leak is autorelased objects. Autoreleased objects hang around until the autorelease pool to which they belong is drained. Depending on memory conditions, they may look like they're leaking during one run but then they don't the next run.

See Avoiding, finding and removing memory leaks in Cocoa to learn how to track down memory leaks.

Edit01:

You might get away with it but I wouldn't recommend it. If it leaks while Apple is testing it you stand a good chance of being rejected.

As a quality issue, it depends on how bad the leaks are and how long they can go on during real world use. Every app probably leaks a few bytes here and there. (For example, there are known leaks in some of the frameworks.) If the leaks are very small, they won't cause problems especially on an app that only runs for a short time. However, if the leaks are larger or the app is designed to run for a long time, then the leaks will eventually bring the app down.

For example, suppose you have a program like the weather app. As a quality issue, it really wouldn't matter if it leaked a bit because the weather app is used quickly. People open it, look at the weather and then close it. The leaks don't have time to accumulation. On the other hand, if you had an app like a web browser or a eReader which people leave open for long periods the leaks could accumulate and bring the app down.

In short, like all other programming task, tracking down leaks is a tradeoff between perceived quality versus development. It is very common to spend more resources tracking down a trivial but common bug than to track down a serious but very rare one.

I would reiterate that the memory leak detection methods in the leak above will eventually locate the leak. If you spend the time on it you will eventually find it.

Answer 2

It's extremely unlikely to be the framework. Don't forget that there are hundreds (thousands?) of developers out there using it so the chances of someone not noticing a bug there is rather slimmer than code that's only been reviewed by yourself.