Fix WPF inference UI thread blocking and add busy indicator

[yeelam-gordon]

Summary

The WPF WindowsML sample's RunInference call was blocking the UI thread, risking freezes on larger models. This PR fixes the threading issue and adds a visual busy indicator.

Changes

1. Move inference to background thread (Task.Run)

• InferenceEngine.RunInference is synchronous (calls session.Run). Even though the calling method is async, prior await calls resume on the UI thread via WPF's SynchronizationContext, so RunInference still blocks the UI thread.
• Wrapped in await Task.Run(...) to offload to a thread pool thread.

2. Add indeterminate ProgressBar busy indicator

• Added a ProgressBar with IsIndeterminate=True that appears during inference and model loading.
• Added SetBusy(bool) helper that toggles the progress bar and disables interactive buttons (Run Inference, Select Image, Load/Reload Model) to prevent double-clicks.
• Applied to both RunInferenceButton_Click and ReloadSessionButton_Click with try/finally.
• Removed the old Dispatcher.Invoke render-flush workaround (no longer needed).

Testing

• Built successfully with dotnet build (0 errors, 0 warnings)
• Ran the app via dotnet run and verified the window launches correctly

Fixes ADO #61791035

[Copilot]

Pull request overview

This PR updates the WindowsML WPF sample to avoid UI freezes during inference by running the synchronous ONNX Runtime session.Run(...) work off the UI thread, and adds a busy indicator to communicate/guard “work in progress” states.

Changes:

• Add a SetBusy(bool) helper to show an indeterminate progress bar and disable user actions during long-running work.
• Offload InferenceEngine.RunInference(...) to a background thread via Task.Run(...).
• Wrap model reload in try/catch/finally to reliably clear the busy state and surface errors in the results textbox.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
Samples/WindowsML/cs-wpf/MainWindow.xaml.cs	Adds SetBusy, moves inference to Task.Run, and adds busy-state handling around model reload/inference.
Samples/WindowsML/cs-wpf/MainWindow.xaml	Adds a hidden-by-default indeterminate ProgressBar used as the busy indicator.

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[Copilot]

SetBusy() disables the three buttons but leaves other interactive controls enabled (e.g., EpCombo, DeviceCombo, AllowProviderDownloadCheckBox). Because LoadModelAndLabelsAsync() reads these values after await points, the user can change selections mid-load and end up creating a session with a different EP/device than the one they clicked with. Consider disabling those inputs while busy (or snapshotting their values before any awaits) so model load is deterministic.

Suggested change

	SelectImageButton.IsEnabled = !busy;
	SelectImageButton.IsEnabled = !busy;
	EpCombo.IsEnabled = !busy;
	DeviceCombo.IsEnabled = !busy;
	AllowProviderDownloadCheckBox.IsEnabled = !busy;

[Copilot]

SetBusy() computes RunInferenceButton.IsEnabled based on _session and _selectedImagePath, but SelectImageButton_Click elsewhere still sets RunInferenceButton.IsEnabled = true unconditionally. That can re-enable the button when _session is null (model not loaded) and undermines the new centralized enable/disable logic. Consider updating the image-selection path to call a single helper (e.g., SetBusy(false) / UpdateUiState()) instead of directly toggling RunInferenceButton.IsEnabled so the enabled state is consistent everywhere.

[Copilot]

Task.Run(() => InferenceEngine.RunInference(_session, ...)) captures the _session field and runs inference on a background thread, but MainWindow_Closed calls Dispose() which disposes _session without coordinating with any in-flight inference task. Closing the window during inference can therefore dispose the session while session.Run(...) is executing, which can lead to crashes or undefined behavior (native resources). Consider capturing _session into a local variable before starting the task and coordinating shutdown (e.g., track/await the inference task on close, or prevent disposal until the background work completes / is canceled).

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

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[Copilot]

SelectImageButton_Click now disables the Run Inference button when _session is null, but the status text still says "Click 'Run Inference'" even when inference can’t be run yet. Update the message to reflect whether the model is loaded (e.g., prompt to load/reload the model first when _session is null).

Suggested change

	ResultsTextBox.Text = "Image selected. Click 'Run Inference' to classify the image.";
	ResultsTextBox.Text = _session != null
	? "Image selected. Click 'Run Inference' to classify the image."
	: "Image selected. Load or reload the model first to enable inference.";

[Copilot]

SetBusy disables EP/device selection and provider download, but leaves the Perf Mode radio buttons enabled. Since Perf Mode is read during model load and affects session creation, it should also be disabled while busy to avoid users changing configuration mid-load/inference and getting inconsistent behavior.

[Copilot]

RunInferenceButton_Click captures _session into a local session for Task.Run, but then calls ExtractResults(_session, results) using the field again. If _session changes (or is disposed) across the awaited calls, results extraction can use a different session’s metadata or hit a null/disposed session. Use the same captured non-null session for both RunInference and ExtractResults, and capture it before the first await in the method to keep it consistent for the whole inference operation.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[Copilot]

Running inference on a background thread introduces a new lifecycle/concurrency edge case: the window can be closed while the Task.Run inference is still executing, and MainWindow.Dispose() will dispose _session concurrently with session.Run. This can lead to ObjectDisposedException or native failures. Consider preventing window close while busy, or tracking the in-flight inference task and awaiting it (or otherwise coordinating) before disposing the session/environment.

Suggested change

	using var results = await Task.Run(() => InferenceEngine.RunInference(session, inputTensor));
	using var results = InferenceEngine.RunInference(session, inputTensor);

[Copilot]

SetBusy(bool) unconditionally sets DeviceCombo.IsEnabled and EpCombo.IsEnabled to !busy, which can override the intended enabled/disabled state managed by PopulateDeviceCombo (e.g., when only one device type exists or when there are no devices for the selected EP). After an inference/model load completes, this can leave DeviceCombo enabled with no valid selections and cause LoadModelAndLabelsAsync to prompt for a device type that cannot be selected. Consider restoring each control to its logical enabled state (e.g., recompute from current EP/devices, or disable a parent container while busy instead of forcing individual IsEnabled values).

Suggested change

	private void SetBusy(bool busy)
	{
	BusyIndicator.Visibility = busy ? Visibility.Visible : Visibility.Collapsed;
	RunInferenceButton.IsEnabled = !busy && _session != null && !string.IsNullOrEmpty(_selectedImagePath);
	ReloadSessionButton.IsEnabled = !busy;
	SelectImageButton.IsEnabled = !busy;
	EpCombo.IsEnabled = !busy;
	DeviceCombo.IsEnabled = !busy;
	private bool _epComboEnabledBeforeBusy;
	private bool _deviceComboEnabledBeforeBusy;
	private void SetBusy(bool busy)
	{
	if (busy)
	{
	_epComboEnabledBeforeBusy = EpCombo.IsEnabled;
	_deviceComboEnabledBeforeBusy = DeviceCombo.IsEnabled;
	}
	BusyIndicator.Visibility = busy ? Visibility.Visible : Visibility.Collapsed;
	RunInferenceButton.IsEnabled = !busy && _session != null && !string.IsNullOrEmpty(_selectedImagePath);
	ReloadSessionButton.IsEnabled = !busy;
	SelectImageButton.IsEnabled = !busy;
	EpCombo.IsEnabled = busy ? false : _epComboEnabledBeforeBusy;
	DeviceCombo.IsEnabled = busy ? false : _deviceComboEnabledBeforeBusy;

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[Copilot]

SetBusy(true) disables DeviceCombo, but LoadModelAndLabelsAsync uses DeviceCombo.IsEnabled to decide whether to read DeviceCombo.SelectedItem (and whether to require a device selection). When ReloadSessionButton_Click calls SetBusy(true) before LoadModelAndLabelsAsync, the chosen device type will always be treated as null, which can change EP/device selection behavior. Consider capturing the EP/device selection before calling SetBusy(true), or update LoadModelAndLabelsAsync to use a separate “device selection required” signal (e.g., based on available device types / item count) rather than IsEnabled, since IsEnabled is now also used for the busy UI state.

Suggested change

	{
	SetBusy(true);
	{
	var deviceComboWasEnabled = DeviceCombo.IsEnabled;
	var selectedDevice = DeviceCombo.SelectedItem;
	SetBusy(true);
	// Preserve the user's device-selection state for model loading.
	// LoadModelAndLabelsAsync uses DeviceCombo.IsEnabled/SelectedItem to decide
	// whether a device selection is required and which device to use. SetBusy(true)
	// temporarily disables the combo for UI purposes, so restore the pre-busy state
	// before loading to avoid changing EP/device selection behavior.
	DeviceCombo.IsEnabled = deviceComboWasEnabled;
	DeviceCombo.SelectedItem = selectedDevice;

[Copilot]

ImageProcessor.LoadImageFileAsync returns a VideoFrame (disposable). Unlike the WinUI/WinForms versions of this sample, this handler doesn’t dispose the videoFrame, which can leak native resources/file handles across repeated inferences. Use a using/Dispose pattern for the returned VideoFrame (and ensure any downstream objects that hold it are disposed as needed).

Suggested change

	var videoFrame = await ImageProcessor.LoadImageFileAsync(_selectedImagePath);
	using var videoFrame = await ImageProcessor.LoadImageFileAsync(_selectedImagePath);

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

Samples/WindowsML/cs-wpf/MainWindow.xaml.cs:233

• RunInferenceButton_Click 的前置校验同时覆盖了“未选图片”和“模型未加载(_session==null)”两种情况，但提示文本固定为“Please select an image first.”。在本 PR 中你已经在选图后根据 _session 是否为 null 给出了不同提示，这里建议也区分两种情况（例如分别提示先加载模型 / 先选择图片），避免用户在模型未加载时被误导。

            if (string.IsNullOrEmpty(_selectedImagePath) || _session == null)
            {
                ResultsTextBox.Text = "Please select an image first.";
                return;

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