Clipboard Chaos!

Note: this content originally from http://mygreenpaste.blogspot.com. If you are reading it from some other site, please take the time to visit My Green Paste, Inc. Thank you.

OK, so perhaps chaos is a bit of a harsh word here. But the clipboard was recently driving me nuts! All I was trying to do was copy some text to it, and the operation was failing. Of course, as it was an ad hoc app, I didn't have any kind of error handling. The app worked just fine on one system, but running the app on another system (a virtual machine) consistently resulted in failure to copy the text to the clipboard.

Ultimately, I was able to determine what process was preventing my app from putting data in the clipboard, but I haven't yet found a decent workaround for when the problem happens. It's not critical for me, as the act of copying the text to the clipboard is more of a nicety than a requirement.

Anyway, using P/Invoke and System.Diagnostics, I found that vmusrvc.exe - the Virtual PC "Virtual Machine User Services" - had the clipboard open. Using the timestamps from Process Monitor's Profiling Events (generated at 100 ms intervals), and the timestamp of the failed operation from my app, I was able to determine the stack of vmusrvc.exe:

ntdll.dll	KiFastSystemCallRet
vmusrvc.exe	vmusrvc.exe + 0x9a17
vmusrvc.exe	vmusrvc.exe + 0x9c24
vmusrvc.exe	vmusrvc.exe + 0x91f8
vmusrvc.exe	vmusrvc.exe + 0x907f
USER32.dll	InternalCallWinProc + 0x28
USER32.dll	UserCallWinProcCheckWow + 0x150
USER32.dll	DispatchClientMessage + 0xa3
USER32.dll	__fnDWORD + 0x24
ntdll.dll	KiUserCallbackDispatcher + 0x13
vmusrvc.exe	vmusrvc.exe + 0x2d29
vmusrvc.exe	vmusrvc.exe + 0xdba6
kernel32.dll	BaseProcessStart + 0x23

No parameters, of course, and symbol information for vmusrvc.exe does not appear to be available, but obviously user32.dll is processing some message. I may look into this more at a later point.

To find the process that was interfering with my clipboard work, I used P/Invoke to call GetOpenClipboardWindow() and then GetWindowThreadProcessId(), passing in the handle returned by GetOpenClipboardWindow(). Then, finding the process' executable name was just a matter of using the Modules collection of the Process instance returned by passing in the process id retrieved by GetWindowThreadProcessId() to System.Diagnostics.Process.GetProcessById().

The following code:

using System.Runtime.InteropServices;
using System.Diagnostics;
...
string data = "aasdlkjasdlk alkjsdl kajsdlkj al";
try
{
    Clipboard.SetData( System.Windows.Forms.DataFormats.Text, data );
}
catch( ExternalException ee )
{
    LogIt( ee.ToString() );
    IntPtr hWnd = GetOpenClipboardWindow();
    if( IntPtr.Zero != hWnd )
    {
        uint pid = 0;
        uint tid = GetWindowThreadProcessId( hWnd, out pid );
        LogIt( "Process with hWnd {0}, PID {1} ({1:x}), TID {2} ({2:x}), " +
                "name {3} has the clipboard", hWnd, pid, tid,
                Process.GetProcessById( (int)pid ).Modules[0].FileName );
    }
}

Resulted in the following output:

2008-03-25 00:54:45.4938864--> System.Runtime.InteropServices.ExternalException: Requested Clipboard operation did not succeed.
 at System.Windows.Forms.Clipboard.ThrowIfFailed(Int32 hr)
 at System.Windows.Forms.Clipboard.SetDataObject(Object data, Boolean copy, Int32 retryTimes, Int32 retryDelay)
 at System.Windows.Forms.Clipboard.SetData(String format, Object data)
 at Clippy.Form1.button1_Click(Object sender, EventArgs e)
2008-03-25 00:54:45.5339440--> Process with hWnd 65716 (65716), PID 1492 (5d4), TID 1496 (5d8), name C:\Program Files\Virtual Machine Additions\vmusrvc.exe has the clipboard

Interestingly, trying an alternative method of the Clipboard to set the content also failed. The Clipboard.SetDataObject() overload that takes a retryTimes and retryDelay parameter failed in the same fashion after roughly ten seconds when invoked as follows:

Clipboard.SetDataObject( data, false, 100, 100 );

I tried variations on retryTimes and retryDelay, to no avail.

Not sure what vmusrvc.exe is doing with the clipboard (probably has to do with monitoring it for host / guest VM interaction), but the act of setting the contents of the clipboard didn't fail 100% of the time in the VM. Often enough to make it extremely unreliable, though. During "normal" system usage, I was not able to cause a failure when running the app on a non-virtual (actual?) system.

Use C# to Find What Services are Running in a Process

Note: this content originally from http://mygreenpaste.blogspot.com. If you are reading it from some other site, please take the time to visit My Green Paste, Inc. Thank you.

Recently, an individual going by the moniker 'hi' posted a comment to Setting the Priority of a Service Process via Script:

How would I, if I want to, find which services are part of a particular svchost.exe? Can in be done in C#?

Thanks!

I replied via comment, but one has even less control over formatting in comments than one does in the actual blog posting, so I figured I would post the response here as well.

=================

Tasklist.exe with the /svc param can tell you, as can Process Explorer. You can also inspect the registry to determine what services would load with what SVCHOST group (see "Troubleshooting Performance Issues with Automatic Updates" for more details).

As far as C# code, the following requires a reference to System.Management. Invoke the program, passing it the process id of the process you're curious about, and it will output the services running in that process.

using System;
using System.Management;

namespace MyGreenPaste
{
  class Program
  {
    static void Main( string[] args )
    {
      if( args.GetLength( 0 ) <= 0 )
      {
        Console.WriteLine( "Usage: {0} pid",
          System.IO.Path.GetFileName(
            System.Diagnostics.Process.GetCurrentProcess().
              MainModule.FileName ) );
        Console.WriteLine( "  where pid is the process id " +
          "of a process hosting at least one service" );
        return;
      }

      try
      {
        ManagementObjectSearcher mos =
          new ManagementObjectSearcher( "root\\CIMV2",
            string.Format( "SELECT * FROM Win32_Service " +
              "where ProcessId={0}", args[0] ) );
        foreach( ManagementObject result in mos.Get() )
        {
          Console.WriteLine( "{0} -> {1}", result["Name"],
            result["DisplayName"] );
        }
      }
      catch( ManagementException mex )
      {
          Console.WriteLine( "** Error querying WMI:{0}{1}",
            System.Environment.NewLine, mex.Message );
      }
    }
  }
}

Setting the Priority of a Service Process via Script

Previously (here and here), I've written about isolating shared services so that they run in their own process, with a specific focus on the Windows Update Automatic Updates Service (wuauserv) that typically runs in the NETSVCS SVCHOST.EXE instance. One thing that can be done once this is accomplished is to lower the priority of the process so that when the service winds up consuming 100% of the CPU, the system doesn't become unresponsive.

Since we're dealing with a service, setting the priority of such a SVCHOST.EXE process can become problematic - the service may already be running, or, because it is a service, it is not started as non-service processes are, so one is not able to use START / [LOW NORMAL HIGH REALTIME ABOVENORMAL BELOWNORMAL] to impose a priority when the process starts. One can use a utility like Task Manager or Process Explorer to set the priority of a process on an ad hoc basis, but when the service restarts or the system reboots one has to remember to set the priority again.

Though not an ideal solution the following scripts (VBS using WMI, and PowerShell) can be used to set the priority of the SVCHOST.EXE instance hosting the isolated Windows Update Automatic Updates Service service to "below normal". Note that no check is done to ensure that the SVCHOST.EXE instance is only hosting one service - if wuauserv is found to be a service inside of the process, the priority is adjusted. Note also that no error handling is implemented.

I'll try to format the code so it looks nice, but I fear I will be limited...

Here's the code for the VBS / WMI script:

Const BELOW_NORMAL = 16384
Set objWMIService = GetObject("winmgmts:\\.\root\CIMV2")
Set colServices = objWMIService.ExecQuery( _
    "SELECT * FROM Win32_Service where name='wuauserv'")
For Each oService in colServices
    Set colProcesses = objWMIService.ExecQuery( _
        "SELECT * FROM Win32_Process where ProcessId=" & oService.ProcessId )
    For Each oProcess in colProcesses
        oProcess.SetPriority(BELOW_NORMAL)
    Next
Next

Here's the code for the PowerShell script:

(gps -id (get-wmiobject win32_service  where {$_.name -eq "wuauserv"}).ProcessId).PriorityClass="BelowNormal"

The different values for the priority parameter of the SetPriority method of the Win32_Process WMI class can be found in the documentation for the SetPriority method.

The different values for the PriorityClass in the PowerShell script are "Normal", "Idle", "High", "RealTime", "BelowNormal", or "AboveNormal". Or, to get a list of the available options, one can use the following PowerShell command:

[ENUM]::getNames("System.Diagnostics.ProcessPriorityClass")

Once the script is in place and working, one can cause it to be invoked at will, or via scheduled task at specific times, or after logon, or any other way that one can get something to happen when Windows boots or a user logs on.

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