Our staff is back at work on Goldenseal Pro. The first thing we faced was a new problem while editing list items. The OK and Cancel buttons used to work fine, but suddenly they didn’t. It turned into a journey down the rabbit hole of Cocoa memory management.
Memory is a general problem for all programmers. Apps need to use many small chunks of RAM: thousands, sometimes millions of them. If you don’t delete them when done, it’s a memory leak. Leaks cause the app to gradually use up more and more memory space. Eventually it will get slow. Pile up enough leaks, and it will crash. Web browsers often do that.
Preventing leaks is not easy. Delete something too early, and the program will fail when you access a long-gone bit of memory. Usually the app crashes from that, but sometimes it reads corrupted data and causes a hard-to-fix bug. Wait too long, and there’s no way to go back to tidy up.
The C and C++ programming languages are considered “hard” because they require programmers to manage raw memory. On the other hand, most newer programming languages do the memory management for you. Usually that involves periodic garbage collection: automatically deleting objects from memory, when they are no longer needed.
Apple’s Cocoa framework started out by requiring programmers to manage their own memory, just like C++. It then added its own memory manager in 2010. Rather than garbage collection, Cocoa uses something called ARC (automatic reference counting).
We turned on ARC when we first started programming Goldenseal Pro for Mac. Sometime in the past year or two it was accidentally turned it off, possibly during an Xcode update. The setting is buried in a list of 200+ other build settings, so it’s easy to overlook.
Removing ARC caused no noticeable problems, since the app was never used long enough to show leaks. Finally we noticed the setting this March, and turned ARC back on. That broke the buttons, and a few other things.
Our staff has worked with ARC long enough now that I feel confident in saying it’s the worst of both worlds. Yet another complaint about Cocoa.
It’s possible to write code in Python, Java, Javascript or other garbage-collected languages, and simply not worry about memory. It’s all taken care of for you. During run time there may be weird multi-second delays as the app cleans up memory, but it’s a small price to pay for convenience.
It’s also possible to use C or C++, and manage memory reliably. Many tricks exist to make it easier. We used them for the original Goldenseal, and it almost never leaks or crashes. Recent versions of C++ provide even better tools for managing memory. We use them in any new code we write.
With its in-between approach, ARC is definitely not mindless. It makes you decide whether to make connections “strong” or “weak”. It sometimes deletes things unexpectedly. It also is hard to debug. There are tricks to help track down memory problems, but nothing as simple as in C++.
Despite all that, the buttons are working again. Then for a while, the app crashed when editing a second list item. That is fixed too. Both were general “object lifetime” problems caused by ARC. They also applied to code in other places, so all those are also fixed now. Sometimes it’s one step backwards, two steps forward.
Dennis Kolva
Programming Director
TurtleSoft.com
