Kill child process when parent process is killed

Question

From this forum, credit to 'Josh'.

Application.Quit() and Process.Kill() are possible solutions, but have proven to be unreliable. When your main application dies, you are still left with child processes running. What we really want is for the child processes to die as soon as the main process dies.

The solution is to use "job objects" http://msdn.microsoft.com/en-us/library/ms682409(VS.85).aspx.

The idea is to create a "job object" for your main application, and register your child processes with the job object. If the main process dies, the OS will take care of terminating the child processes.

public enum JobObjectInfoType
{
    AssociateCompletionPortInformation = 7,
    BasicLimitInformation = 2,
    BasicUIRestrictions = 4,
    EndOfJobTimeInformation = 6,
    ExtendedLimitInformation = 9,
    SecurityLimitInformation = 5,
    GroupInformation = 11
}

[StructLayout(LayoutKind.Sequential)]
public struct SECURITY_ATTRIBUTES
{
    public int nLength;
    public IntPtr lpSecurityDescriptor;
    public int bInheritHandle;
}

[StructLayout(LayoutKind.Sequential)]
struct JOBOBJECT_BASIC_LIMIT_INFORMATION
{
    public Int64 PerProcessUserTimeLimit;
    public Int64 PerJobUserTimeLimit;
    public Int16 LimitFlags;
    public UInt32 MinimumWorkingSetSize;
    public UInt32 MaximumWorkingSetSize;
    public Int16 ActiveProcessLimit;
    public Int64 Affinity;
    public Int16 PriorityClass;
    public Int16 SchedulingClass;
}

[StructLayout(LayoutKind.Sequential)]
struct IO_COUNTERS
{
    public UInt64 ReadOperationCount;
    public UInt64 WriteOperationCount;
    public UInt64 OtherOperationCount;
    public UInt64 ReadTransferCount;
    public UInt64 WriteTransferCount;
    public UInt64 OtherTransferCount;
}

[StructLayout(LayoutKind.Sequential)]
struct JOBOBJECT_EXTENDED_LIMIT_INFORMATION
{
    public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
    public IO_COUNTERS IoInfo;
    public UInt32 ProcessMemoryLimit;
    public UInt32 JobMemoryLimit;
    public UInt32 PeakProcessMemoryUsed;
    public UInt32 PeakJobMemoryUsed;
}

public class Job : IDisposable
{
    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
    static extern IntPtr CreateJobObject(object a, string lpName);

    [DllImport("kernel32.dll")]
    static extern bool SetInformationJobObject(IntPtr hJob, JobObjectInfoType infoType, IntPtr lpJobObjectInfo, uint cbJobObjectInfoLength);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool AssignProcessToJobObject(IntPtr job, IntPtr process);

    private IntPtr m_handle;
    private bool m_disposed = false;

    public Job()
    {
        m_handle = CreateJobObject(null, null);

        JOBOBJECT_BASIC_LIMIT_INFORMATION info = new JOBOBJECT_BASIC_LIMIT_INFORMATION();
        info.LimitFlags = 0x2000;

        JOBOBJECT_EXTENDED_LIMIT_INFORMATION extendedInfo = new JOBOBJECT_EXTENDED_LIMIT_INFORMATION();
        extendedInfo.BasicLimitInformation = info;

        int length = Marshal.SizeOf(typeof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION));
        IntPtr extendedInfoPtr = Marshal.AllocHGlobal(length);
        Marshal.StructureToPtr(extendedInfo, extendedInfoPtr, false);

        if (!SetInformationJobObject(m_handle, JobObjectInfoType.ExtendedLimitInformation, extendedInfoPtr, (uint)length))
            throw new Exception(string.Format("Unable to set information.  Error: {0}", Marshal.GetLastWin32Error()));
    }

    #region IDisposable Members

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    #endregion

    private void Dispose(bool disposing)
    {
        if (m_disposed)
            return;

        if (disposing) {}

        Close();
        m_disposed = true;
    }

    public void Close()
    {
        Win32.CloseHandle(m_handle);
        m_handle = IntPtr.Zero;
    }

    public bool AddProcess(IntPtr handle)
    {
        return AssignProcessToJobObject(m_handle, handle);
    }

}

Looking at the constructor ...

JOBOBJECT_BASIC_LIMIT_INFORMATION info = new JOBOBJECT_BASIC_LIMIT_INFORMATION();
info.LimitFlags = 0x2000;

The key here is to setup the job object properly. In the constructor I'm setting the "limits" to 0x2000, which is the numeric value for JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE.

MSDN defines this flag as:

Causes all processes associated with the job to terminate when the last handle to the job is closed.

Once this class is setup...you just have to register each child process with the job. For example:

[DllImport("user32.dll", SetLastError = true)]
public static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

Excel.Application app = new Excel.ApplicationClass();

uint pid = 0;
Win32.GetWindowThreadProcessId(new IntPtr(app.Hwnd), out pid);
 job.AddProcess(Process.GetProcessById((int)pid).Handle);

This answer started with @Matt Howells' excellent answer plus others (see links in the code below). Improvements:

• Supports 32-bit and 64-bit.
• Fixes some problems in @Matt Howells' answer:
  1. The small memory leak of extendedInfoPtr
  2. The 'Win32' compile error, and
  3. A stack-unbalanced exception I got in the call to CreateJobObject (using Windows 10, Visual Studio 2015, 32-bit).
• Names the Job, so if you use SysInternals, for example, you can easily find it.
• Has a somewhat simpler API and less code.

Here's how to use this code:

// Get a Process object somehow.
Process process = Process.Start(exePath, args);
// Add the Process to ChildProcessTracker.
ChildProcessTracker.AddProcess(process);

To support Windows 7 requires:

• A simple app.manifest change as @adam smith describes.
• Registry settings to be added if you are using Visual Studio.

In my case, I didn't need to support Windows 7, so I have a simple check at the top of the static constructor below.

/// <summary>
/// Allows processes to be automatically killed if this parent process unexpectedly quits.
/// This feature requires Windows 8 or greater. On Windows 7, nothing is done.</summary>
/// <remarks>References:
///  https://stackoverflow.com/a/4657392/386091
///  https://stackoverflow.com/a/9164742/386091 </remarks>
public static class ChildProcessTracker
{
    /// <summary>
    /// Add the process to be tracked. If our current process is killed, the child processes
    /// that we are tracking will be automatically killed, too. If the child process terminates
    /// first, that's fine, too.</summary>
    /// <param name="process"></param>
    public static void AddProcess(Process process)
    {
        if (s_jobHandle != IntPtr.Zero)
        {
            bool success = AssignProcessToJobObject(s_jobHandle, process.Handle);
            if (!success && !process.HasExited)
                throw new Win32Exception();
        }
    }

    static ChildProcessTracker()
    {
        // This feature requires Windows 8 or later. To support Windows 7 requires
        //  registry settings to be added if you are using Visual Studio plus an
        //  app.manifest change.
        //  https://stackoverflow.com/a/4232259/386091
        //  https://stackoverflow.com/a/9507862/386091
        if (Environment.OSVersion.Version < new Version(6, 2))
            return;

        // The job name is optional (and can be null) but it helps with diagnostics.
        //  If it's not null, it has to be unique. Use SysInternals' Handle command-line
        //  utility: handle -a ChildProcessTracker
        string jobName = "ChildProcessTracker" + Process.GetCurrentProcess().Id;
        s_jobHandle = CreateJobObject(IntPtr.Zero, jobName);

        var info = new JOBOBJECT_BASIC_LIMIT_INFORMATION();

        // This is the key flag. When our process is killed, Windows will automatically
        //  close the job handle, and when that happens, we want the child processes to
        //  be killed, too.
        info.LimitFlags = JOBOBJECTLIMIT.JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;

        var extendedInfo = new JOBOBJECT_EXTENDED_LIMIT_INFORMATION();
        extendedInfo.BasicLimitInformation = info;

        int length = Marshal.SizeOf(typeof(JOBOBJECT_EXTENDED_LIMIT_INFORMATION));
        IntPtr extendedInfoPtr = Marshal.AllocHGlobal(length);
        try
        {
            Marshal.StructureToPtr(extendedInfo, extendedInfoPtr, false);

            if (!SetInformationJobObject(s_jobHandle, JobObjectInfoType.ExtendedLimitInformation,
                extendedInfoPtr, (uint)length))
            {
                throw new Win32Exception();
            }
        }
        finally
        {
            Marshal.FreeHGlobal(extendedInfoPtr);
        }
    }

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
    static extern IntPtr CreateJobObject(IntPtr lpJobAttributes, string name);

    [DllImport("kernel32.dll")]
    static extern bool SetInformationJobObject(IntPtr job, JobObjectInfoType infoType,
        IntPtr lpJobObjectInfo, uint cbJobObjectInfoLength);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool AssignProcessToJobObject(IntPtr job, IntPtr process);

    // Windows will automatically close any open job handles when our process terminates.
    //  This can be verified by using SysInternals' Handle utility. When the job handle
    //  is closed, the child processes will be killed.
    private static readonly IntPtr s_jobHandle;
}

public enum JobObjectInfoType
{
    AssociateCompletionPortInformation = 7,
    BasicLimitInformation = 2,
    BasicUIRestrictions = 4,
    EndOfJobTimeInformation = 6,
    ExtendedLimitInformation = 9,
    SecurityLimitInformation = 5,
    GroupInformation = 11
}

[StructLayout(LayoutKind.Sequential)]
public struct JOBOBJECT_BASIC_LIMIT_INFORMATION
{
    public Int64 PerProcessUserTimeLimit;
    public Int64 PerJobUserTimeLimit;
    public JOBOBJECTLIMIT LimitFlags;
    public UIntPtr MinimumWorkingSetSize;
    public UIntPtr MaximumWorkingSetSize;
    public UInt32 ActiveProcessLimit;
    public Int64 Affinity;
    public UInt32 PriorityClass;
    public UInt32 SchedulingClass;
}

[Flags]
public enum JOBOBJECTLIMIT : uint
{
    JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE = 0x2000
}

[StructLayout(LayoutKind.Sequential)]
public struct IO_COUNTERS
{
    public UInt64 ReadOperationCount;
    public UInt64 WriteOperationCount;
    public UInt64 OtherOperationCount;
    public UInt64 ReadTransferCount;
    public UInt64 WriteTransferCount;
    public UInt64 OtherTransferCount;
}

[StructLayout(LayoutKind.Sequential)]
public struct JOBOBJECT_EXTENDED_LIMIT_INFORMATION
{
    public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
    public IO_COUNTERS IoInfo;
    public UIntPtr ProcessMemoryLimit;
    public UIntPtr JobMemoryLimit;
    public UIntPtr PeakProcessMemoryUsed;
    public UIntPtr PeakJobMemoryUsed;
}

---

I carefully tested both the 32-bit and 64-bit versions of the structs by programmatically comparing the managed and native versions to each other (the overall size as well as the offsets for each member).

I've tested this code on Windows 7, 8, and 10.

This post is intended as an extension to @Matt Howells' answer, specifically for those who run into problems with using Job Objects under Vista or Win7, especially if you get an access denied error ('5') when calling AssignProcessToJobObject.

tl;dr

To ensure compatibility with Vista and Win7, add the following manifest to the .NET parent process:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
  <v3:trustInfo xmlns:v3="urn:schemas-microsoft-com:asm.v3">
    <v3:security>
      <v3:requestedPrivileges>
        <v3:requestedExecutionLevel level="asInvoker" uiAccess="false" />
      </v3:requestedPrivileges>
    </v3:security>
  </v3:trustInfo>
  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
    <!-- We specify these, in addition to the UAC above, so we avoid Program Compatibility Assistant in Vista and Win7 -->
    <!-- We try to avoid PCA so we can use Windows Job Objects -->
    <!-- See https://stackoverflow.com/questions/3342941/kill-child-process-when-parent-process-is-killed -->

    <application>
      <!--The ID below indicates application support for Windows Vista -->
      <supportedOS Id="{e2011457-1546-43c5-a5fe-008deee3d3f0}"/>
      <!--The ID below indicates application support for Windows 7 -->
      <supportedOS Id="{35138b9a-5d96-4fbd-8e2d-a2440225f93a}"/>
    </application>
  </compatibility>
</assembly>

Note that when you add new manifest in Visual Studio 2012 it will contain the above snippet already so you do not need to copy it from hear. It will also include a node for Windows 8.

full explanation

Your job association will fail with an access denied error if the process you're starting is already associated with another job. Enter Program Compatibility Assistant, which, starting in Windows Vista, will assign all kinds of processes to its own jobs.

In Vista you can mark your application to be excluded from PCA by simply including an application manifest. Visual Studio seems to do this for .NET apps automatically, so you're fine there.

A simple manifest no longer cuts it in Win7. [1] There, you have to specifically specify that you're compatible with Win7 with the tag in your manifest. [2]

This led me to worry about Windows 8. Will I have to change my manifest once again? Apparently there's a break in the clouds, as Windows 8 now allows a process to belong to multiple jobs. [3] So I haven't tested it yet, but I imagine that this madness will be over now if you simply include a manifest with the supportedOS information.

Tip 1: If you're developing a .NET app with Visual Studio, as I was, here [4] are some nice instructions on how to customize your application manifest.

Tip 2: Be careful with launching your application from Visual Studio. I found that, after adding the appropriate manifest, I still had problems with PCA when launching from Visual Studio, even if I used Start without Debugging. Launching my application from Explorer worked, however. After manually adding devenv for exclusion from PCA using the registry, starting applications that used Job Objects from VS started working as well. [5]

Tip 3: If you ever want to know if PCA is your problem, try launching your application from the command line, or copy the program to a network drive and run it from there. PCA is automatically disabled in those contexts.

[1] http://blogs.msdn.com/b/cjacks/archive/2009/06/18/pca-changes-for-windows-7-how-to-tell-us-you-are-not-an-installer-take-2-because-we-changed-the-rules-on-you.aspx

[2] http://ayende.com/blog/4360/how-to-opt-out-of-program-compatibility-assistant

[3] http://msdn.microsoft.com/en-us/library/windows/desktop/ms681949(v=vs.85).aspx: "A process can be associated with more than one job in Windows 8"

[4] How can I embed an application manifest into an application using VS2008?

[5] How to stop the Visual Studio debugger starting my process in a job object?

Here's an alternative that may work for some when you have control of the code the child process runs. The benefit of this approach is it doesn't require any native Windows calls.

The basic idea is to redirect the child's standard input to a stream whose other end is connected to the parent, and use that stream to detect when the parent has gone away. When you use System.Diagnostics.Process to start the child, it's easy to ensure its standard input is redirected:

Process childProcess = new Process();
childProcess.StartInfo = new ProcessStartInfo("pathToConsoleModeApp.exe");
childProcess.StartInfo.RedirectStandardInput = true;

childProcess.StartInfo.CreateNoWindow = true; // no sense showing an empty black console window which the user can't input into

And then, on the child process, take advantage of the fact that Reads from the standard input stream will always return with at least 1 byte until the stream is closed, when they will start returning 0 bytes. An outline of the way I ended up doing this is below; my way also uses a message pump to keep the main thread available for things other than watching standard in, but this general approach could be used without message pumps too.

using System;
using System.IO;
using System.Threading;
using System.Windows.Forms;

static int Main()
{
    Application.Run(new MyApplicationContext());
    return 0;
}

public class MyApplicationContext : ApplicationContext
{
    private SynchronizationContext _mainThreadMessageQueue = null;
    private Stream _stdInput;

    public MyApplicationContext()
    {
        _stdInput = Console.OpenStandardInput();

        // feel free to use a better way to post to the message loop from here if you know one ;)    
        System.Windows.Forms.Timer handoffToMessageLoopTimer = new System.Windows.Forms.Timer();
        handoffToMessageLoopTimer.Interval = 1;
        handoffToMessageLoopTimer.Tick += new EventHandler((obj, eArgs) => { PostMessageLoopInitialization(handoffToMessageLoopTimer); });
        handoffToMessageLoopTimer.Start();
    }

    private void PostMessageLoopInitialization(System.Windows.Forms.Timer t)
    {
        if (_mainThreadMessageQueue == null)
        {
            t.Stop();
            _mainThreadMessageQueue = SynchronizationContext.Current;
        }

        // constantly monitor standard input on a background thread that will
        // signal the main thread when stuff happens.
        BeginMonitoringStdIn(null);

        // start up your application's real work here
    }

    private void BeginMonitoringStdIn(object state)
    {
        if (SynchronizationContext.Current == _mainThreadMessageQueue)
        {
            // we're already running on the main thread - proceed.
            var buffer = new byte[128];

            _stdInput.BeginRead(buffer, 0, buffer.Length, (asyncResult) =>
                {
                    int amtRead = _stdInput.EndRead(asyncResult);

                    if (amtRead == 0)
                    {
                        _mainThreadMessageQueue.Post(new SendOrPostCallback(ApplicationTeardown), null);
                    }
                    else
                    {
                        BeginMonitoringStdIn(null);
                    }
                }, null);
        }
        else
        {
            // not invoked from the main thread - dispatch another call to this method on the main thread and return
            _mainThreadMessageQueue.Post(new SendOrPostCallback(BeginMonitoringStdIn), null);
        }
    }

    private void ApplicationTeardown(object state)
    {
        // tear down your application gracefully here
        _stdInput.Close();

        this.ExitThread();
    }
}

Caveats to this approach:

1. the actual child .exe that is launched must be a console application so it remains attached to stdin/out/err. As in the above example, I easily adapted my existing application that used a message pump (but didn't show a GUI) by just creating a tiny console project that referenced the existing project, instantiating my application context and calling Application.Run() inside the Main method of the console .exe.

2. Technically, this merely signals the child process when the parent exits, so it will work whether the parent process exited normally or crashed, but its still up to the child processes to perform its own shutdown. This may or may not be what you want...