Kill child process when parent process is killed

Question

I\'m creating new processes using System.Diagnostics.Process class from my application.

I want this processes to be killed when/if my application has cr

Answer 1

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.

Answer 2

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);

Answer 3

Yet another addition to the abundant richness of solutions proposed so far....

The problem with many of them is that they rely upon the parent and child process to shut down in an orderly manner, which isn't always true when development is underway. I found that my child process was often being orphaned whenever I terminated the parent process in the debugger, which required me to kill the orphaned process(es) with Task Manager in order to rebuild my solution.

The solution: Pass the parent process ID in on the commandline (or even less invasive, in the environment variables) of the child process.

In the parent process, the process ID is available as:

Process.CurrentProcess.Id;

In the child process:

Process parentProcess = Process.GetProcessById(parentProcessId);
parentProcess.Exited += (s, e) =>
{
    // clean up what you can.
    this.Dispose();
    // maybe log an error
    ....

    // And terminate with prejudice! 
    //(since something has already gone terribly wrong)
    Process.GetCurrentProcess().Kill();
};

I am of two minds as to whether this is acceptable practice in production code. On the one hand, this should never happen. But on the other hand, it may mean the difference between restarting a process, and rebooting a production server. And what should never happen often does.

And it sure is useful while debugging orderly shutdown problems.