Time Profiler & hangs

Time Profiler: where CPU time actually goes

Time Profiler samples every thread many times a second and builds a call tree from those samples — the more samples land inside a function, the more CPU time it's costing. Sort by heaviest stack and you get a ranked list of "what PawWalk is actually spending its CPU on" instead of a guess. It's the tool for "why does this screen feel sluggish," whether the cost is on the main thread or a background one.

A hang is a specific, user-visible case: the main thread blocked long enough that the UI stops responding — taps don't register, animations freeze. Apple's guidance flags anything past roughly 250ms of main-thread unresponsiveness as a hang; Instruments' Hangs (and Animation Hitches) templates surface these automatically while you use the app, with an adjustable threshold.