How to Identify Processes Locking a File in .NET Using the Restart Manager API?

Utilizing the .NET Framework to Identify Processes Locking Files

Traditionally, pinpointing the specific process holding a file lock within the .NET framework presented a significant challenge. However, with modern Windows advancements, the Restart Manager API now provides a reliable mechanism to track this information.

Solution Implementation:

The following code snippet offers a robust method for identifying processes that have established locks on a designated file:

public static List<Process> IdentifyFileLockers(string filePath)
{
    uint sessionHandle;
    string sessionKey = Guid.NewGuid().ToString();
    List<Process> lockedByProcesses = new List<Process>();

    int result = RmStartSession(out sessionHandle, 0, sessionKey);
    if (result != 0) throw new Exception("Failed to initiate restart session.  Unable to identify file locker.");

    try
    {
        const int ERROR_MORE_DATA = 234;
        uint processesNeeded = 0,
            processesReturned = 0,
            rebootReasons = RmRebootReasonNone;

        string[] resources = new string[] { filePath }; // Targeting a single resource.

        result = RmRegisterResources(sessionHandle, (uint)resources.Length, resources, 0, null, 0, null);

        if (result != 0) throw new Exception("Resource registration failed.");

        //Note: A race condition exists here. The initial RmGetList() call returns
        //      the total process count.  Subsequent RmGetList() calls to retrieve
        //      actual processes might encounter an increased count.
        result = RmGetList(sessionHandle, out processesNeeded, ref processesReturned, null, ref rebootReasons);

        if (result == ERROR_MORE_DATA)
        {
            // Allocate an array to store process information.
            RM_PROCESS_INFO[] processInfoArray = new RM_PROCESS_INFO[processesNeeded];
            processesReturned = processesNeeded;

            // Retrieve the process list.
            result = RmGetList(sessionHandle, out processesNeeded, ref processesReturned, processInfoArray, ref rebootReasons);
            if (result == 0)
            {
                lockedByProcesses = new List<Process>((int)processesReturned);

                // Iterate through results and populate the return list.
                for (int i = 0; i < processesReturned; i++)
                {
                    try
                    {
                        //Attempt to get the process by ID.  May fail if the process is already gone.
                        Process p = Process.GetProcessById(processInfoArray[i].Process.dwProcessId);
                        lockedByProcesses.Add(p);
                    }
                    catch (ArgumentException) { } // Ignore processes that no longer exist.
                }
            }
        }
    }
    finally
    {
        RmEndSession(sessionHandle);
    }

    return lockedByProcesses;
}

Important Note: Executing this code requires unprivileged registry access. If the process lacks the necessary permissions, implementing an IPC mechanism (e.g., a named pipe) to delegate the call to a privileged process is recommended.

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