116: Jittery Moment

iOhYes

Discussion: Time Profiler

• But first: a brief rundown of the Instruments UI

  • Toolbar
    • Record/Stop
    • Pause
    • Target Selection
    • Status display
    • Strategy Selection
      • CPU data
      • Instrument data
      • Thread data
    • Detail/inspector toggles
  • Timeline
    • Plots data along the time your app was sampled
    • Can be filtered and zoomed
    • Disclosure arrow can toggle display of just the current run or of all runs in the trace document
  • Detail
    • Contents vary by Instrument, but this will generally be a table with some representation of the sampled data
  • Inspectors
    • Record Settings
    • Display Settings
    • Extended detail (often the heaviest stack trace)

• What is Time Profiler?

  • An Instrument providing sample-based analysis of an application’s activity
  • Periodically samples the call stack to determine where an app is spending its time
    • These are instantaneous samples. They don’t track the duration of a function call, but rather how many times when sampled was the application currently in said function call.
    • No distinction between a fast function called many times and a slow function called few times
    • Extremely fast functions may not get sampled at all, if they happen to occur in between samples
  • Provides a detail view listing call trees, optionally separated by thread and/or state, allowing the developer to drive down into calls to identify areas that may need to be optimized
    • Weight - Percentage of samples in which a function appeared and an aggregate summary of samples (count * sample interval)
    • Self Weight - Aggregate summary of samples in which the function was at the top of the call stack
    • Symbol Name - The thing represented in the current row (may be a function, method, closure/block, thread, or app)
    • Category
    • Additional columns available:
      • Count
      • Self Count
      • Library

Picks

John

• SelfControl

Darryl

• WWDC 2016 Session 418 - Using Time Profiler in Instruments

Alternative show title suggestions

• Try harder
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• my code, vs not my code
• expected or unexpected
• notion of runs

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