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
Examples of Flutter's layered architecture
This directory contains several self-contained examples that illustrate Flutter's layered architecture.
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raw/ These examples show how to program against the lowest layer of the system. They manually receive input packets and construct composited scenes.
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rendering/ These examples use Flutter's render tree to structure your app using a retained tree of visual objects. These objects coordinate to determine their size and position on screen and to handle events.
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widgets/ These examples use Flutter's widgets to build more elaborate apps using a reactive framework.
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services/ These examples use services available in Flutter to interact with the host platform.
To run each example, specify the demo file on the flutter run
command line, for example:
flutter run raw/spinning_square.dart
flutter run rendering/spinning_square.dart
flutter run widgets/spinning_square.dart