Added keep alive setting

[craigloewen-msft]

Summary of the Pull Request

Added a setting to WSL settings to keep the WSL VM alive at all times.

PR Checklist

Very simple change.
Adds a 'InstanceIdleTimeout' setting and a "WSL keep VM alive" setting to WSL settings.

Detailed Description of the Pull Request / Additional comments

Did this in WSL settings only, no major code changes.

Validation Steps Performed

Validated settings loaded correctly.

[Copilot]

Pull request overview

This PR adds a new WSL Settings UI toggle to keep the WSL VM running indefinitely by driving the existing wsl2.vmIdleTimeout setting into a negative value (which the service interprets as “do not idle-terminate”).

Changes:

• Add a “Keep WSL VM alive” toggle to Optional Features, and disable the VM idle timeout expander when keep-alive is active.
• Extend the Optional Features view model with keep-alive/enablement properties and related change notifications.
• Add en-US localized strings (header/description and accessibility text) for the new setting.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/windows/wslsettings/Views/Settings/OptionalFeaturesPage.xaml	Adds keep-alive toggle and disables the idle-timeout expander based on view model state.
src/windows/wslsettings/ViewModels/Settings/OptionalFeaturesViewModel.cs	Adds computed properties for keep-alive and VM idle-timeout enablement, and updates change notification flow.
localization/strings/en-US/Resources.resw	Adds localized strings for the new keep-alive setting and toggle accessibility metadata.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

src/windows/wslsettings/Views/Settings/OptionalFeaturesPage.xaml:62

• InstanceIdleTimeout is used to implement “Keep WSL VM alive” by setting a negative timeout, but this header TextBlock formats the raw value via MillisecondsStringConverter. With keep-alive enabled, this will display "-1 milliseconds" (and similarly for other negative values), which is user-unfriendly and doesn’t reflect the toggle semantics.

                <ctControls:SettingsExpander x:Name="InstanceIdleTimeoutExpander" x:Uid="Settings_InstanceIdleTimeout" IsEnabled="{x:Bind ViewModel.InstanceIdleTimeoutEnabled, Mode=OneWay}">
                    <TextBlock Style="{StaticResource TextBlockSettingStyle}" Text="{x:Bind ViewModel.InstanceIdleTimeout, Mode=OneWay, Converter={StaticResource MillisecondsStringConverter}}"/>

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (2)

src/windows/wslsettings/ViewModels/Settings/OptionalFeaturesViewModel.cs:93

• Toggling “Keep WSL VM alive” off always writes _defaultInstanceIdleTimeout back to InstanceIdleTimeout, which can discard a user’s previously configured distribution idle timeout (e.g., user sets 30000ms → enables keep-alive → disables keep-alive → value becomes default 15000ms). Consider preserving/restoring the last non-negative timeout value so the toggle doesn’t lose user configuration.

    public bool IsOnKeepVMAlive
    {
        get { return _instanceIdleTimeout!.Int32Value < 0; }
        set
        {
            Set(ref _instanceIdleTimeout!, value ? -1 : _defaultInstanceIdleTimeout, nameof(IsOnKeepVMAlive));
            OnPropertyChanged(nameof(InstanceIdleTimeout));
            OnPropertyChanged(nameof(InstanceIdleTimeoutEnabled));
            OnPropertyChanged(nameof(VMIdleTimeoutEnabled));
            InstanceIdleTimeout_ResetEnabled = !Equals(_defaultInstanceIdleTimeout, _instanceIdleTimeout!.Int32Value);
        }

src/windows/wslsettings/Views/Settings/SettingsApplyHelper.cs:180

• Pending changes formatting will currently show negative idle timeouts as “-1 ms”. Since the service treats values < 0 as “never idle-terminate”, the apply dialog should format negative InstanceIdleTimeout/VMIdleTimeout as a user-friendly localized value (e.g. “Never”) instead of a negative duration.

                    case WslConfigEntry.InitialAutoProxyTimeout:
                    case WslConfigEntry.InstanceIdleTimeout:
                    case WslConfigEntry.VMIdleTimeout:
                        return string.Format("Settings_MillisecondsStringFormat".GetLocalized(), (int)value);
                    default:

[benhillis]

Nice, the mechanism checks out - _VmIsIdle() only returns true once no running instance has a valid client id, so pinning instanceIdleTimeout to a negative value does keep the VM up. A few things I hit while reading through it.

[benhillis]

When the toggle is on, InstanceIdleTimeout is -1, and MillisecondsStringConverter only special-cases ulong 0, so this collapsed summary ends up reading literally -1 ms. Same thing shows up in the apply-changes dialog, since SettingsApplyHelper.FormatValue runs the new entry through Settings_MillisecondsStringFormat - so toggling Keep WSL VM alive produces a confirmation line like Distribution idle timeout: -1 ms for a field the user never touched.

Could we have the converter return null (or something like Never) for negative values, and map the toggle to Settings_KeepVMAlive/Header in the apply summary?

[benhillis]

Toggling off always snaps back to the built-in default, so someone who had instanceIdleTimeout = 5000 and flips this on and then off again silently loses their 5000. Worth stashing the previous positive value in a field and restoring that, falling back to _defaultInstanceIdleTimeout only when there wasn't one.

[benhillis]

Two small wording things here. This is backed by general.instanceIdleTimeout, which also applies to WSL1 instances (see the LxssInstance path in LxssUserSession.cpp), so Keep WSL VM alive undersells what it actually does. It also doesn't start anything - it only stops an already-running VM from being shut down, and wsl --shutdown still works. Might be worth reflecting both in the description so nobody expects the VM to come up on boot.