enum PerfCounters
Swift
enum PerfCountersProcess-wide counters for work the frame pipeline did.
These exist because wall-clock alone is a bad regression gate: the same machine varies 20-30% run to run, so a threshold loose enough not to cry wolf is too loose to catch a 2x algorithmic regression until it is a 4x one. Counts have no variance. "How many lines did we shape to draw this frame" is 41 or it is 200,000, and the second one is the bug — the exact bug that made opening a 10 MB log in TraceLoom take 601 ms.
So LavaBench gates on counters and reports times. A counter moving is
a hard failure; a time moving is a number to look at.
Incremented unconditionally rather than behind an isEnabled flag. Each
site is per-shaped-line or per-Yoga-measure — thousands per frame at the
very worst, against work that is orders of magnitude more expensive — and
a branch on a second global would cost more than the add it guards.
Sources/LavaUI/PerfCounters.swift:19
Properties
nonisolated(unsafe) static var imageDecodes: IntImages decoded + uploaded because ImageStore missed.
Sources/LavaUI/PerfCounters.swift:39
nonisolated(unsafe) static var imageEvictions: IntImages dropped by the byte budget. With imageDecodes, this is the
thrash signal: a scroll that decodes and evicts the same covers over
and over shows up here long before it shows up as a slow frame.
Sources/LavaUI/PerfCounters.swift:43
nonisolated(unsafe) static var layoutPasses: IntLayoutHost.calculateLayout calls, including the lazy-window settle
re-passes (which is why this can exceed one per frame).
Sources/LavaUI/PerfCounters.swift:37
nonisolated(unsafe) static var lineWraps: IntLogical lines broken into rows by a soft-wrap pass — the ones the wrap
cache could not reuse. Shaping alone does not show this: a line whose
text is unchanged is served from UIFont's shape cache and never
reaches HarfBuzz, but it still pays for its advances to be laid out and
its breaks to be found. On an edit this should be a handful; anything
proportional to the buffer means the cache was thrown away.
Sources/LavaUI/PerfCounters.swift:32
nonisolated(unsafe) static var textShapeHits: IntLines served from that cache. textShapes + textShapeHits is the
number of shaping requests, which is the interesting one for emit:
it should track visible rows, not buffer size.
Sources/LavaUI/PerfCounters.swift:25
nonisolated(unsafe) static var textShapes: IntLines handed to HarfBuzz because UIFont's shape cache missed.
Sources/LavaUI/PerfCounters.swift:21
nonisolated(unsafe) static var yogaMeasures: IntLeafNode.measureForYoga calls — Yoga measure-function invocations.
Sources/LavaUI/PerfCounters.swift:34
Methods
static func reset()Not documented.
Sources/LavaUI/PerfCounters.swift:45
static func snapshot() -> [(name: String, value: Int)]Ordered so a printed table has a stable column order.
Sources/LavaUI/PerfCounters.swift:56