Thursday, November 06, 2008

When Is A Leak Not A Leak

I was sent a bug report on some software I had written a while back wherein it would become less and less responsive over time till it just sort of died. Sounds like a leak.

But when I hooked it up to the Leaks Instrument, I saw no leaks. No red peaks at all. Must not be a leak then.

But one more look. The net objects allocated were going up and up and up. This should not happen, the application should have reached an equilibrium point of net objects allocated, and oscillated around it.

So, I let it run for a while in the Objects Allocated instrument, and then examined the blocks which were being allocated and not deallocated. Turns out I had an object, an audio player, which had a scheduled NSTimer associated with it. When I released the player, it was still being referred to by the NSTimer, so it did not get deallocated. And in this case, I was creating one of these every second or so (probably not a good idea), which meant that not only was the memory leaking, but all those timers were adding overhead to the event loop. No wonder it crawled to a halt. So remember to invalidate unwanted timers.