c# – Hung Office interop processes


Suppose an application needs to use Office interop. (no options) Everyone knows that he creates office applications without an interface and performs work through them.

Well, what if the user incorrectly completed work with the program? For example, killed through the task manager. It turns out that office applications remain hanging in the processes.

Can this be prevented? If not, is it possible to understand when the application is started (repeatedly) that there is garbage in the processes that remains from the previous launch and crash these processes without affecting the real office applications (for example, the user launched Excel.)


Alternatively, using Win32 tools, you can combine the application and the processes launched from it into a job ( Job ) then the Interop processes will be completed along with the parent application.

To do this, you will need to create a job using CreateJobObject , and then add the created processes to the job using AssignProcessToJobObject

There is a similar discussion in English: " Kill child process when parent process is killed ". From @Ron's answer, you can take the wrapper class code for ChildProcessTracker :

/// <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="processHandle"></param>
    public static void AddProcess(int processHandle)
        if (s_jobHandle != IntPtr.Zero)
            bool success = AssignProcessToJobObject(s_jobHandle, new IntPtr(processHandle));
            if (!success)
                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))

        // 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);


        // 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.

        var 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(s_jobHandle, JobObjectInfoType.ExtendedLimitInformation,
                extendedInfoPtr, (uint)length))
                throw new Win32Exception();

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

    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

    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;

public enum JOBOBJECTLIMIT : uint

public struct IO_COUNTERS
    public UInt64 ReadOperationCount;
    public UInt64 WriteOperationCount;
    public UInt64 OtherOperationCount;
    public UInt64 ReadTransferCount;
    public UInt64 WriteTransferCount;
    public UInt64 OtherTransferCount;

    public JOBOBJECT_BASIC_LIMIT_INFORMATION BasicLimitInformation;
    public IO_COUNTERS IoInfo;
    public UIntPtr ProcessMemoryLimit;
    public UIntPtr JobMemoryLimit;
    public UIntPtr PeakProcessMemoryUsed;
    public UIntPtr PeakJobMemoryUsed;

, and use it to register Excel processes as children:

static extern int GetWindowThreadProcessId(int hWnd, out int lpdwProcessId);

var app = new Microsoft.Office.Interop.Excel.Application();
int processId;
GetWindowThreadProcessId(app.Hwnd, out processId);

, and then the OS will kill them along with the parent process.

I recommend that you read the documentation and read the comments in the discussion at the link, there may be nuances with support for different versions of the OS and Visual Studio, when running with limited rights, when starting the parent application from other processes.

If not, is it possible to understand when the application is started (repeatedly) that there is garbage in the processes that remains from the previous launch and crash these processes without affecting the real office applications (for example, the user launched Excel.)

I doubt there is a reliable method. An Excel process started by an old process is no different than a process started by the current/other applications/user. It is possible, as suggested by @VadimTagil, to write code that will save running processes to permanent storage (disk / database / registry) and kill them according to certain logic. Another option is to move the Excel generation into separate task processes that do not depend on the main application.

In general, if there is no garbage left in the normal course of the application, then problems will arise only in exceptional cases (a process killed from the outside), the processing of which can be left to the user. Make sure that Marshal.ReleaseComObject is called on all objects and that all processes are terminated so that the job can probably be dispensed with.

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