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Graceful Shutdown

When a PCF app is stopped (i.e. cf stop), it receives a CTRL_SHUTDOWN_EVENT and is allowed 10 seconds to gracefully shutdown. In order to use this feature, the app must provide a control handler as seen in the example below. See [2] for more information on how control handlers work.

Graceful shutdown is not supported on deployments running versions prior to Windows Server 2019.

Add the following class to your application

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;

namespace MyApplication
{
    public static class ApplicationLifecycle
    {
        private static readonly CancellationTokenSource _appShutdownCts = new CancellationTokenSource();
        private static readonly ManualResetEvent _shutdownCompleteHandle = new ManualResetEvent(false);

        private static readonly List<Func<Task>> _shutdownDelegates = new List<Func<Task>>();

        static ApplicationLifecycle()
        {
            SetConsoleEventHandler(OnTerminateCommand);
        }

        public static WaitHandle ShutdownCompleteHandle => _shutdownCompleteHandle;

        private static bool OnTerminateCommand(CtrlEvent eventtype)
        {
            Shutdown();
            return true;
        }

        public static void Shutdown()
        {
            _appShutdownCts.Cancel();
            Task.WhenAll(_shutdownDelegates.Select(x => x())).Wait(TimeSpan.FromSeconds(10));
            _shutdownCompleteHandle.Set();
        }

        public static CancellationToken RegisterForGracefulShutdown(Func<Task> serviceCleanup)
        {
            _shutdownDelegates.Add(serviceCleanup);
            return _appShutdownCts.Token;
        }
        
        
        public delegate bool ConsoleEventDelegate(CtrlEvent eventType);

        private static ConsoleEventDelegate _handler; // Keeps it from getting garbage collected

        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern bool SetConsoleCtrlHandler(ConsoleEventDelegate callback, bool add);

        public static void SetConsoleEventHandler(ConsoleEventDelegate handler)
        {
            _handler = handler;
            SetConsoleCtrlHandler(_handler, true);
        }

        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern bool GenerateConsoleCtrlEvent(CtrlEvent sigevent, int dwProcessGroupId);
        public enum CtrlEvent
        {
            CTRL_C_EVENT = 0,
            CTRL_BREAK_EVENT = 1,
            CTRL_CLOSE_EVENT = 5,
            CTRL_LOGOFF_EVENT = 5,
            CTRL_SHUTDOWN_EVENT = 6
        }
    }
}

In Global.asmx Application_Start method, register each component that wants to participate in graceful shutdown using RegisterForGracefulShutdown method.

Example:

ApplicationLifecycle.RegisterForGracefulShutdown(async () =>
{
	Console.WriteLine("Doing some gracefulshutdown tasks");
	await Task.Delay(1000);
    Console.WriteLine("Shutdown tasks complete");
});

You must also add the following hook to Application_Stop to ensure the application doesn’t exit before all the components had a chance to shutdown:

protected void Application_Stop()
{
    ApplicationLifecycle.ShutdownCompleteHandle.WaitOne();
}

Example steps to see logs written after CTRL_SHUTDOWN_EVENT is received:

cf push YourApp -s windows -b hwc_buildpack
curl YourApp.<domain>.com
cf stop YourApp
cf logs YourApp --recent | grep Graceful
[APP/PROC/WEB/0] OUT Doing some gracefulshutdown tasks
[APP/PROC/WEB/0] OUT Shutdown tasks complete

References

[1] Microsoft Docs: SetConsoleCtrlHandler

[2] Microsoft Docs: HandlerRoutine callback function

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