ce61eda70c
## Background
The Windows runner has a race at startup:
1. **Platform thread**: creates a hidden window
2. **Platform thread**: launches the Flutter engine
3. **UI/Raster threads**: renders the first frame
4. **Platform thread**: Registers a callback to show the window once the next frame has been rendered.
Steps 3 and 4 happen in parallel and it is possible for step 3 to complete before step 4 starts. In this scenario, the next frame callback is never called and the window is never shown.
As a result the `windows_startup_test`'s test, which [verifies that the "show window" callback is called](1f09a8662d/dev/integration_tests/windows_startup_test/windows/runner/flutter_window.cpp (L60-L64)), can flake if the first frame is rendered before the show window callback has been registered.
## Solution
This change makes the runner schedule a frame after it registers the next frame callback. If step 3 hasn't completed yet, this no-ops as a frame is already scheduled. If step 3 has already completed, a new frame will be rendered, which will call the next frame callback and show the window.
Part of https://github.com/flutter/flutter/issues/119415
See this thread for alternatives that were considered: https://github.com/flutter/engine/pull/42061#issuecomment-1550080722
Flutter Tools
This section of the Flutter repository contains the command line developer tools for building Flutter applications.
Working on Flutter Tools
Be sure to follow the instructions on CONTRIBUTING.md to set up your development environment. Further, familiarize yourself with the style guide, which we follow.
Setting up
First, ensure that the Dart SDK and other necessary artifacts are available by invoking the Flutter Tools wrapper script. In this directory run:
$ flutter --version
Running the Tool
To run Flutter Tools from source, in this directory run:
$ dart bin/flutter_tools.dart
followed by command-line arguments, as usual.
Running the analyzer
To run the analyzer on Flutter Tools, in this directory run:
$ flutter analyze
Writing tests
As with other parts of the Flutter repository, all changes in behavior must be
tested.
Tests live under the test/ subdirectory.
-
Hermetic unit tests of tool internals go under
test/general.shardand must run in significantly less than two seconds. -
Tests of tool commands go under
test/commands.shard. Hermetic tests go under itshermetic/subdirectory. Non-hermetic tests go under itspermeablesub-directory. Avoid adding tests here and prefer writing either a unit test or a full integration test. -
Integration tests (e.g. tests that run the tool in a subprocess) go under
test/integration.shard. -
Slow web-related tests go in the
test/web.sharddirectory.
In general, the tests for the code in a file called file.dart should
go in a file called file_test.dart in the subdirectory that matches
the behavior of the test.
The dart_test.yaml file configures the timeout for these tests to be
15 minutes. The test.dart script that is used in CI overrides this
to two seconds for the test/general.shard directory, to catch
behaviour that is unexpectedly slow.
Please avoid setting any other timeouts.
Using local engine builds in integration tests
The integration tests can be configured to use a specific local engine
variant by setting the FLUTTER_LOCAL_ENGINE environment variable to the
name of the local engine (e.g. "android_debug_unopt"). If the local engine build
requires a source path, this can be provided by setting the FLUTTER_LOCAL_ENGINE_SRC_PATH
environment variable. This second variable is not necessary if the flutter and
engine checkouts are in adjacent directories.
export FLUTTER_LOCAL_ENGINE=android_debug_unopt
flutter test test/integration.shard/some_test_case
Running the tests
To run all of the unit tests:
$ flutter test test/general.shard
The tests in test/integration.shard are slower to run than the tests
in test/general.shard. Depending on your development computer, you
might want to limit concurrency. Generally it is easier to run these
on CI, or to manually verify the behavior you are changing instead of
running the test.
The integration tests also require the FLUTTER_ROOT environment
variable to be set. The full invocation to run everything might
therefore look something like:
$ export FLUTTER_ROOT=~/path/to/flutter-sdk
$ flutter test --concurrency 1
This may take some time (on the order of an hour). The unit tests alone take much less time (on the order of a minute).
You can run the tests in a specific file, e.g.:
$ flutter test test/general.shard/utils_test.dart
Forcing snapshot regeneration
To force the Flutter Tools snapshot to be regenerated, delete the following files:
$ rm ../../bin/cache/flutter_tools.stamp ../../bin/cache/flutter_tools.snapshot