Add IsRestarting property to Umbraco application notifications

[ronaldbarendse]

Prerequisites

• I have added steps to test this contribution in the description below

Description

This is a minor addition to PR #11857 that adds a very useful IsRestarting property to the UmbracoApplicationStartingNotification, UmbracoApplicationStartedNotification, UmbracoApplicationStoppingNotification and UmbracoApplicationStoppedNotification.

In 'normal' applications the running process is killed when it's stopped (and the application state is clean when started again), but that's not the case when Umbraco restarts: it's only stopping and starting the runtime, not the whole application.

So if you only want to execute some code on the initial startup of Umbraco, handling the UmbracoApplicationStartingNotification could result in running it twice when Umbraco has installed or upgraded (as that's when the Umbraco runtime gets restarted). In hindsight, we should've probably named these UmbracoRuntime...Notification instead 🤡

Testing can be done using the same steps as described in the related PR, but you can replace the UmbracoApplicationNotificationHandler with the class below to log the value of the new property:

public class UmbracoApplicationNotificationHandler : INotificationHandler<UmbracoApplicationStartingNotification>, INotificationHandler<UmbracoApplicationStartedNotification>, INotificationHandler<UmbracoApplicationStoppingNotification>, INotificationHandler<UmbracoApplicationStoppedNotification>
{
    private readonly ILogger _logger;

    public UmbracoApplicationNotificationHandler(ILogger<UmbracoApplicationNotificationHandler> logger) => _logger = logger;

    public void Handle(UmbracoApplicationStartingNotification notification) => Log(notification, notification.IsRestarting);

    public void Handle(UmbracoApplicationStartedNotification notification) => Log(notification, notification.IsRestarting);

    public void Handle(UmbracoApplicationStoppingNotification notification) => Log(notification, notification.IsRestarting);

    public void Handle(UmbracoApplicationStoppedNotification notification) => Log(notification, notification.IsRestarting);

    private void Log(INotification notification, bool isRestarting) => _logger.LogInformation("{Type} - {IsRestarting}", notification.GetType().Name, isRestarting);
}

[ronaldbarendse]

If it makes sense, we can even move the IsRestarting property to an interface and/or base class:

public interface IUmbracoApplicationLifetimeNotification : INotification
{
    bool IsRestarting { get; }
}

public abstract class UmbracoApplicationLifetimeNotificationBase : IUmbracoApplicationLifetimeNotification
{
    public UmbracoApplicationLifetimeNotificationBase(bool isRestarting = false) => IsRestarting = isRestarting;

    public bool IsRestarting { get; }
}

I'm a bit undecided on this, as it adds some inheritance/complexity, but removes some duplication (including XML docs).

[ronaldbarendse]

After having another look, adding an IUmbracoApplicationLifetimeNotification interface does add some value: it conceptually groups the notifications and ensures they all use the same property type/name/documentation.

I've also updated the constructors of the notifications, so you need to explicitly pass in a value for this property. I've only left the original constructors for the existing UmbracoApplicationStartingNotification and UmbracoApplicationStoppingNotification, but obsoleted them, so they can be removed in a next major release.

The new interface also allows the UmbracoApplicationNotificationHandler (used for testing) to be a little bit cleaner too:

public class UmbracoApplicationNotificationHandler : INotificationHandler<UmbracoApplicationStartingNotification>, INotificationHandler<UmbracoApplicationStartedNotification>, INotificationHandler<UmbracoApplicationStoppingNotification>, INotificationHandler<UmbracoApplicationStoppedNotification>
{
    private readonly ILogger _logger;

    public UmbracoApplicationNotificationHandler(ILogger<UmbracoApplicationNotificationHandler> logger) => _logger = logger;

    public void Handle(UmbracoApplicationStartingNotification notification) => Log(notification);

    public void Handle(UmbracoApplicationStartedNotification notification) => Log(notification);

    public void Handle(UmbracoApplicationStoppingNotification notification) => Log(notification);

    public void Handle(UmbracoApplicationStoppedNotification notification) => Log(notification);

    private void Log(IUmbracoApplicationLifetimeNotification notification) => _logger.LogInformation("{Type} - {IsRestarting}", notification.GetType().Name, notification.IsRestarting);
}

[bergmania]

Cherry picked to 9.3rc