How do I find out which process is locking a file using .NET?

It is very complex to invoke Win32 from C#.

You should use the tool Handle.exe.

After that your C# code have to be the following:

string fileName = @"c:\aaa.doc";//Path to locked file

Process tool = new Process();
tool.StartInfo.FileName = "handle.exe";
tool.StartInfo.Arguments = fileName+" /accepteula";
tool.StartInfo.UseShellExecute = false;
tool.StartInfo.RedirectStandardOutput = true;
tool.Start();           
tool.WaitForExit();
string outputTool = tool.StandardOutput.ReadToEnd();

string matchPattern = @"(?<=\s+pid:\s+)\b(\d+)\b(?=\s+)";
foreach(Match match in Regex.Matches(outputTool, matchPattern))
{
    Process.GetProcessById(int.Parse(match.Value)).Kill();
}

One of the good things about handle.exe is that you can run it as a subprocess and parse the output.

We do this in our deployment script - works like a charm.

I had issues with stefan's solution. Below is a modified version which seems to work well.

using System;
using System.Collections;
using System.Diagnostics;
using System.Management;
using System.IO;

static class Module1
{
    static internal ArrayList myProcessArray = new ArrayList();
    private static Process myProcess;

    public static void Main()
    {
        string strFile = "c:\\windows\\system32\\msi.dll";
        ArrayList a = getFileProcesses(strFile);
        foreach (Process p in a)
        {
            Debug.Print(p.ProcessName);
        }
    }

    private static ArrayList getFileProcesses(string strFile)
    {
        myProcessArray.Clear();
        Process[] processes = Process.GetProcesses();
        int i = 0;
        for (i = 0; i <= processes.GetUpperBound(0) - 1; i++)
        {
            myProcess = processes[i];
            //if (!myProcess.HasExited) //This will cause an "Access is denied" error
            if (myProcess.Threads.Count > 0)
            {
                try
                {
                    ProcessModuleCollection modules = myProcess.Modules;
                    int j = 0;
                    for (j = 0; j <= modules.Count - 1; j++)
                    {
                        if ((modules[j].FileName.ToLower().CompareTo(strFile.ToLower()) == 0))
                        {
                            myProcessArray.Add(myProcess);
                            break;
                            // TODO: might not be correct. Was : Exit For
                        }
                    }
                }
                catch (Exception exception)
                {
                    //MsgBox(("Error : " & exception.Message)) 
                }
            }
        }

        return myProcessArray;
    }
}

UPDATE

If you just want to know which process(es) are locking a particular DLL, you can execute and parse the output of tasklist /m YourDllName.dll. Works on Windows XP and later. See

What does this do? tasklist /m "mscor*"

This works for DLLs locked by other processes. This routine will not find out for example that a text file is locked by a word process.

C#:

using System.Management; 
using System.IO;   

static class Module1 
{ 
static internal ArrayList myProcessArray = new ArrayList(); 
private static Process myProcess; 

public static void Main() 
{ 

    string strFile = "c:\\windows\\system32\\msi.dll"; 
    ArrayList a = getFileProcesses(strFile); 
    foreach (Process p in a) { 
        Debug.Print(p.ProcessName); 
    } 
} 


private static ArrayList getFileProcesses(string strFile) 
{ 
    myProcessArray.Clear(); 
    Process[] processes = Process.GetProcesses; 
    int i = 0; 
    for (i = 0; i <= processes.GetUpperBound(0) - 1; i++) { 
        myProcess = processes(i); 
        if (!myProcess.HasExited) { 
            try { 
                ProcessModuleCollection modules = myProcess.Modules; 
                int j = 0; 
                for (j = 0; j <= modules.Count - 1; j++) { 
                    if ((modules.Item(j).FileName.ToLower.CompareTo(strFile.ToLower) == 0)) { 
                        myProcessArray.Add(myProcess); 
                        break; // TODO: might not be correct. Was : Exit For 
                    } 
                } 
            } 
            catch (Exception exception) { 
            } 
            //MsgBox(("Error : " & exception.Message)) 
        } 
    } 
    return myProcessArray; 
} 
} 

VB.Net:

Imports System.Management
Imports System.IO

Module Module1
Friend myProcessArray As New ArrayList
Private myProcess As Process

Sub Main()

    Dim strFile As String = "c:\windows\system32\msi.dll"
    Dim a As ArrayList = getFileProcesses(strFile)
    For Each p As Process In a
        Debug.Print(p.ProcessName)
    Next
End Sub


Private Function getFileProcesses(ByVal strFile As String) As ArrayList
    myProcessArray.Clear()
    Dim processes As Process() = Process.GetProcesses
    Dim i As Integer
    For i = 0 To processes.GetUpperBound(0) - 1
        myProcess = processes(i)
        If Not myProcess.HasExited Then
            Try
                Dim modules As ProcessModuleCollection = myProcess.Modules
                Dim j As Integer
                For j = 0 To modules.Count - 1
                    If (modules.Item(j).FileName.ToLower.CompareTo(strFile.ToLower) = 0) Then
                        myProcessArray.Add(myProcess)
                        Exit For
                    End If
                Next j
            Catch exception As Exception
                'MsgBox(("Error : " & exception.Message))
            End Try
        End If
    Next i
    Return myProcessArray
End Function
End Module