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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
76 lines
2.2 KiB
C++
76 lines
2.2 KiB
C++
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "flutter_window.h"
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#include <optional>
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#include "flutter/generated_plugin_registrant.h"
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FlutterWindow::FlutterWindow(const flutter::DartProject& project)
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: project_(project) {}
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FlutterWindow::~FlutterWindow() {}
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bool FlutterWindow::OnCreate() {
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if (!Win32Window::OnCreate()) {
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return false;
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}
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RECT frame = GetClientArea();
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// The size here must match the window dimensions to avoid unnecessary surface
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// creation / destruction in the startup path.
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flutter_controller_ = std::make_unique<flutter::FlutterViewController>(
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frame.right - frame.left, frame.bottom - frame.top, project_);
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// Ensure that basic setup of the controller was successful.
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if (!flutter_controller_->engine() || !flutter_controller_->view()) {
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return false;
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}
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RegisterPlugins(flutter_controller_->engine());
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SetChildContent(flutter_controller_->view()->GetNativeWindow());
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flutter_controller_->engine()->SetNextFrameCallback([&]() {
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this->Show();
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});
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// Flutter can complete the first frame before the "show window" callback is
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// registered. Ensure a frame is pending to ensure the window is shown.
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// This no-ops if the first frame hasn't completed yet.
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flutter_controller_->ForceRedraw();
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return true;
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}
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void FlutterWindow::OnDestroy() {
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if (flutter_controller_) {
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flutter_controller_ = nullptr;
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}
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Win32Window::OnDestroy();
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}
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LRESULT
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FlutterWindow::MessageHandler(HWND hwnd, UINT const message,
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WPARAM const wparam,
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LPARAM const lparam) noexcept {
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// Give Flutter, including plugins, an opportunity to handle window messages.
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if (flutter_controller_) {
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std::optional<LRESULT> result =
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flutter_controller_->HandleTopLevelWindowProc(hwnd, message, wparam,
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lparam);
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if (result) {
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return *result;
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}
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}
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switch (message) {
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case WM_FONTCHANGE:
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flutter_controller_->engine()->ReloadSystemFonts();
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break;
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}
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return Win32Window::MessageHandler(hwnd, message, wparam, lparam);
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}
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