Weird CPU usage problem when app is backgrounded

I'm experiencing a very weird CPU usage bug with my audio streaming app.

When the app is in the foreground and playing music, the total device CPU usage is only about 15%. However, as soon as the app is put in the background, the CPU usage spikes to 100% and stays there.

About 40% of this is coming from the app process itself, and roughly the other 60% is coming from the SpringBoard process, which apparently handles a开发者_如何学编程ll Core Animation calls (though I'm not explicitly using Core Animation, I assume that it also handles other UI related activity). Also, according to the "CPU Activity" instrument, most of the additional CPU usage from the app process itself falls into the "graphics" category, though I do see an increase in both the "audio processing" and (strangely) the "foreground app activity" category.

How can I figure out what is causing this problem? Instruments is telling me at high level what is happening, but not why it's happening.

That's extremely odd. However, without any code, it makes it really hard to say anything about anything. Purely based on speculation, I'd say you're updating the UI without knowing it in the background. Perhaps an animation call on -(void)applicationDidEnterBackground? Give us some more to work with! I'm really curious about this now :)

Mystery solved!

Of course I missed the obvious, thank you to Dylan G for pointing me in the right direction. I was running a loop to check the remaining background time. I wasn't sleeping the loop thread at all so it was apparently just running full speed sucking up all CPU power.

I'm not sure why it was looking like it was graphics related and involving the SpringBoard process, but as soon as I added a sleep(1) at the end of the loop, the CPU usage no longer rose when the app was placed in the background. The strange thing is that I'm not calling any UI or graphic related methods in that loop, just calls to [[UIApplication sharedApplication] backgroundTimeRemaining] and accessing some integer and bool properties.

There is still a quick spike of CPU for the second or so after it's placed in the background, and SpringBoard spikes as well, but just for a second, then CPU usage drops back to the same as when the app is running.