applicationDidEnterBackground
アプリケーションがバックグラウンドに入ったときアプリケーションのbackgroundTimeRemaining プロパティで示される残り時間が 0 になる前に処理を終えなくてはならない。この値は最初 10 秒にセットされている（ことが多い？）
処理を終えないとこんな感じで終わらせられる。
Thu Nov 25 11:30:01 xxxxx-no-iPhone BT[4821] : Remain:0.683624 100000127 is prime
Thu Nov 25 11:30:02 xxxxx-no-iPhone SpringBoard[1557] : BT[4821] has active assertions beyond permitted time:
{(
<SBProcessAssertion: 0x94d5ca0> identifier: Suspending process: BT[4821] permittedBackgroundDuration: 10.000000 reason: suspend owner pid:1557 preventSuspend preventThrottleDownCPU preventThrottleDownUI
)}
Thu Nov 25 11:30:02 xxxxx-no-iPhone SpringBoard[1557] : Forcing crash report of BT[4821]...
Thu Nov 25 11:30:02 xxxxx-no-iPhone SpringBoard[1557] : Finished crash reporting.
Thu Nov 25 11:30:02 xxxxx-no-iPhone com.apple.launchd[1] (UIKitApplication:jp.co.xxxxx.BT[0xc343][4821]) : (UIKitApplication:jp.co.xxxxx.BT[0xc343]) Exited: Killed
Thu Nov 25 11:30:02 xxxxx-no-iPhone SpringBoard[1557] : Application 'BT' exited abnormally with signal 9: Killed
Thu Nov 25 11:30:02 xxxxx-no-iPhone ReportCrash[4830] : Saved crashreport to /var/mobile/Library/Logs/CrashReporter/BT_2010-11-25-113002_xxxxx-no-iPhone.plist using uid: 0 gid: 0, synthetic_euid: 501 egid: 0
Saturn on Thu 25 Nov 2010 at 02:45 with 0 comments
