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(for example, flutter build ios --bundle-sksl-path
flutter_01.sksl.json --target=test_driver/app.dart).
test the newly built app.
alternatively, you can write some integration tests to
automate the first three steps using a single command.
for example:
with such integration tests,
you can easily and reliably get the
new SkSLs when the app code changes,
or when flutter upgrades.
such tests can also be used to verify the performance change
before and after the SkSL warm-up.
even better, you can put those tests into a
CI (continuous integration) system so the
SkSLs are generated and tested automatically over the lifetime of an app.
info note
the integration_test package is now the recommended way
to write integration tests. refer to the
integration testing
page for details.
take the original version of flutter gallery as an example.
the CI system is set up to generate SkSLs for every flutter commit,
and verifies the performance, in the transitions_perf_test.dart test.
for more details,
check out the flutter_gallery_sksl_warmup__transition_perf and
flutter_gallery_sksl_warmup__transition_perf_e2e_ios32 tasks.
the worst frame rasterization time is a useful metric from
such integration tests to indicate the severity of shader
compilation jank.
for instance,
the steps above reduce flutter gallery’s shader compilation
jank and speeds up its worst frame rasterization time on a
moto g4 from ~90 ms to ~40 ms. on iPhone 4s,
it’s reduced from ~300 ms to ~80 ms. that leads to the visual
difference as illustrated in the beginning of this article.
<topic_end>
<topic_start>
performance metrics
for a complete list of performance metrics flutter measures per commit, visit
the following sites, click query, and filter the test and
sub_result fields:
<topic_end>
<topic_start>
concurrency and isolates
all dart code runs in isolates,
which are similar to threads,
but differ in that isolates have their own isolated memory.
they do not share state in any way,
and can only communicate by messaging.
by default,
flutter apps do all of their work on a single isolate –
the main isolate.
in most cases, this model allows for simpler programming and
is fast enough that the application’s UI doesn’t become unresponsive.
sometimes though,
applications need to perform exceptionally large computations
that can cause “ui jank” (jerky motion).
if your app is experiencing jank for this reason,
you can move these computations to a helper isolate.
this allows the underlying runtime environment
to run the computation concurrently
with the main UI isolate’s work
and takes advantage of multi-core devices.
each isolate has its own memory
and its own event loop.
the event loop processes
events in the order that they’re added to an event queue.
on the main isolate,
these events can be anything from handling a user tapping in the UI,
to executing a function,
to painting a frame on the screen.
the following figure shows an example event queue
with 3 events waiting to be processed.
for smooth rendering,
flutter adds a “paint frame” event to the event queue
60 times per second(for a 60hz device).
if these events aren’t processed on time,
the application experiences UI jank,
or worse,
become unresponsive altogether.
whenever a process can’t be completed in a frame gap,
the time between two frames,
it’s a good idea to offload the work to another isolate
to ensure that the main isolate can produce 60 frames per second.
when you spawn an isolate in dart,
it can process the work concurrently with the main isolate,
without blocking it.
you can read more about how isolates
and the event loop work in dart on
the concurrency page of the dart
documentation.
<topic_end>
<topic_start>
common use cases for isolates
there is only one hard rule for when you should use isolates,
and that’s when large computations are causing your flutter application
to experience UI jank.
this jank happens when there is any computation that takes longer than
flutter’s frame gap.
any process could take longer to complete,