HostingAbstractionsHostExtensions RunAsync disposes without logging

[snakefoot]

Description

The RunAsync in HostingAbstractionsHostExtensions.cs disposes the Host on exit:

runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostingAbstractionsHostExtensions.cs

Lines 60 to 70 in 2be87c9

	public static async Task RunAsync(this IHost host, CancellationToken token = default)
	{
	try
	{
	await host.StartAsync(token).ConfigureAwait(false);
	await host.WaitForShutdownAsync(token).ConfigureAwait(false);
	}
	finally
	{
	if (host is IAsyncDisposable asyncDisposable)

This disposes the ServiceProvider and the LoggerFactory, so unable to perform any logging after this point.

Inside the Host StartAsync then it nicely logs Starting, but any exception happing in the following code is not caught and logged:

runtime/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs

Lines 56 to 66 in 215b39a

	public async Task StartAsync(CancellationToken cancellationToken = default)
	{
	_logger.Starting();
	using var combinedCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, _applicationLifetime.ApplicationStopping);
	CancellationToken combinedCancellationToken = combinedCancellationTokenSource.Token;
	await _hostLifetime.WaitForStartAsync(combinedCancellationToken).ConfigureAwait(false);
	combinedCancellationToken.ThrowIfCancellationRequested();
	_hostedServices = Services.GetRequiredService<IEnumerable<IHostedService>>();

And because of the dispose, then any logging is impossible on exception:

Reproduction Steps

        var builder = Host.CreateDefaultBuilder();
        builder.ConfigureServices(s => s.AddHostedService<BrokenHostedService>());
        builder.Build().Run();

        class BrokenHostedService : IHostedService
        {
            public Task StartAsync(CancellationToken cancellationToken)
            {
                throw new Exception("Hosted service startup error!");
            }

            public Task StopAsync(CancellationToken cancellationToken)
            {
                return Task.CompletedTask;
            }
        }

Expected behavior

Exception is logged to the Microsoft Console Provider.

Actual behavior

Application crashes without any trace.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

Tagging subscribers to this area: @dotnet/area-extensions-hosting
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

The RunAsync in HostingAbstractionsHostExtensions.cs disposes the Host on exit:

runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostingAbstractionsHostExtensions.cs

Lines 60 to 70 in 2be87c9

	public static async Task RunAsync(this IHost host, CancellationToken token = default)
	{
	try
	{
	await host.StartAsync(token).ConfigureAwait(false);
	await host.WaitForShutdownAsync(token).ConfigureAwait(false);
	}
	finally
	{
	if (host is IAsyncDisposable asyncDisposable)

This disposes the ServiceProvider and the LoggerFactory, so unable to perform any logging after this point.

Inside the Host StartAsync then it nice logs Starting, but any exception happing in the code is not caught and logged:

runtime/src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs

Lines 56 to 59 in 215b39a

	public async Task StartAsync(CancellationToken cancellationToken = default)
	{
	_logger.Starting();

And because of the dispose, then any logging is impossible.

Reproduction Steps

        var builder = Host.CreateDefaultBuilder();
        builder.ConfigureServices(s => s.AddHostedService<BrokenHostedService>());
        builder.Build().Run();

        class BrokenHostedService : IHostedService
        {
            public Task StartAsync(CancellationToken cancellationToken)
            {
                throw new Exception("Hosted service startup error!");
            }

            public Task StopAsync(CancellationToken cancellationToken)
            {
                return Task.CompletedTask;
            }
        }

Expected behavior

Exception is logged to the Microsoft Console Provider.

Actual behavior

Application crashes without any trace.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

Author:	snakefoot
Assignees:	-
Labels:	area-Extensions-Hosting
Milestone:	-

[eerhardt]

The application crashes because an unhandled exception is being thrown and killing the Main thread. StartAsync is called directly on the Main thread, and until you await a Task it continues on the Main thread. See #36063 for more info on that.

You can workaround this by wrapping your StartAsync method in a Task.Run, which will execute your code on a background thread and not block the Main method of the app. However, if you throw an unhandled exception from that background thread, your app won't crash and nothing will be logged unless you log it yourself. See #36017. If you want Hosting to handle the logging of unhandled exceptions, you need to inherit from BackgroundService.

[snakefoot]

Yes I'm aware that with enough effort, then one can add try-catches everywhere in user-code to ensure exception is logged.

But since having the Host-wrapper, that already now performs logging of Host-"Starting" and Host-"Stopped", then to me it would be natural that it also performed logging of Host-"Startup Error" on exception. Thus making the user-code cleaner with more focus on the success path, than the error-path.

[kmcclellan]

I also find it odd that exceptions thrown starting hosted services aren't logged while stopping exceptions are.

I include this boilerplate in my apps as a workaround. Definitely feels less idiomatic than host.RunAsync().

await using ((IAsyncDisposable)(host = builder.Build()))
{
    var logger = host.Services.GetService<ILogger<Program>>();

    try
    {
        await host.StartAsync();
    }
    catch (Exception exception)
    {
        logger?.LogCritical(exception, "Failed to start host");
        throw;
    }

    await host.WaitForShutdownAsync();
}

[steveharter]

Expected behavior

Exception is logged to the Microsoft Console Provider.

This is fixed with #112534