System.Diaganostics.Process.Id Isn't the Same Process Id Shown in Task Manager. Why?

Question

I'm using C#'s System.Diagnostic.Process object.
One of its properties is Id.
The Id this produces is not the same as the PID, shown in Windows Task Manager.
Why is this?

You see, once this process is started.
It launches two other unmanaged processes, for which I can't explicitly get IDs for by object property references.
I have to search through all processes to find them by process name via System.Diagnostics.Process.GetProcesses().

I'm trying to find a reliable way to kill this process and all associated processes by PID, the one that shows in Task Manager.
Is there a better way?

I can't just kill all processes with the associated process names, because that might kill other instances of those processes that have nothing to do with my program.

Gain

If you start the process with System.Diagnostics.Process, then call .Refresh() before checking the ID. The ID is assigned by the OS when the process starts, not when the Process object is instantiated. – Misapprehension

Answer 1

The key is that you don't want to kill your process by Id. In fact, that's a race condition: your spawned process could die and another process could get created with the same Id. Then when you go to kill it, you would end up killing the new process instead of the old one that was already dead.

The most reliable way to kill spawned processes is to put them in a Job object and terminate the Job once your task is completed.

Here's some simple code to implement a Job class:

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

    [DllImport("kernel32.dll")]
    public static extern bool AssignProcessToJobObject(IntPtr hJob, IntPtr hProcess);

    [DllImport("kernel32.dll")]
    public static extern bool TerminateJobObject(IntPtr hJob, uint uExitCode);

    IntPtr job;

    public Process StartProc(string commandLine)
    {
        if (job == IntPtr.Zero)
            job = CreateJobObject(IntPtr.Zero, null);
        ProcessStartInfo si = new ProcessStartInfo(@"c:\windows\system32\cmd.exe");
        si.Arguments = "/c " + commandLine;
        si.CreateNoWindow = false;
        si.UseShellExecute = false;
        Process proc = Process.Start(si);
        AssignProcessToJobObject(job, proc.Handle);
        return proc;
    }

    public void TerminateProc()
    {
        // terminate the Job object, which kills all processes within it
        if (job != null)
            TerminateJobObject(job, 0);
        job = IntPtr.Zero;
    }
}

Centesimal

I did imagine that possibility, but didn't know what to do. Will those unmanage-sub-processes (that are indirectly started by the process I start) be subordinately related to this job object too? So that if I kill the job, all 3 process get killed? – Gain

BTW, I'm scared of code in angle brackets; I don't understand it yet. Are those attributes at the top? Is this code limited to 32 bit architecture? – Gain

Terminating the Job object will terminate the process you started and every process started by it, and so on. And yes, those are attributes at the top in brackets. I haven't run this on a 64-bit machine, but there's no reason to believe it won't work. – Centesimal

Answer 2

I can't reproduce this. I've just run the following code:

foreach (var proc in Process.GetProcesses()
                            .OrderBy(proc => proc.Id))
{
    Console.WriteLine("{0}: {1}", p.Id, p.ProcessName);
}

All the processes listed have matches the PID in Task Manager. This is using Windows 7 - what OS are you using? If you look at other processes, do they match the PID shown in Task Manager?

Osteoblast

Jon, the other two processes (the unmanaged ones started indirectly by the process I start) match. But, the process I start's id is different in task manager, than it is in the property reference via myProcess.Id. – Gain

BTW, I like that .OrderBy method you posted. I didn't know you could do that. – Gain