restart windows explorer.exe from powershell with Windows Restart Manager API

restart_explorer.ps1

# restart-explorer.ps1
# Restarts explorer.exe using Windows Restart Manager.

Add-Type -TypeDefinition @"
using System;
using System.Runtime.InteropServices;
using System.Text;

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct RM_UNIQUE_PROCESS
{
    public int dwProcessId;
    public System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
}

// https://learn.microsoft.com/en-us/windows/win32/api/restartmanager/ns-restartmanager-rm_process_info
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct RM_PROCESS_INFO
{
    public RM_UNIQUE_PROCESS Process;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    public string strAppName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
    public string strServiceShortName;
    public uint ApplicationType;
    public uint AppStatus;
    public uint TSSessionId;
    [MarshalAs(UnmanagedType.Bool)]
    public bool bRestartable;
}

// omitted RmGetFilterList RmAddFilter RmJoinSession RmCancelCurrentTask
public static class RestartManager
{
    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmStartSession(
        out int pSessionHandle,
        int dwSessionFlags,
        StringBuilder strSessionKey
    );

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmRegisterResources(
        int dwSessionHandle,
        uint nFiles,
        [MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPWStr)] string[] rgsFiles,
        uint nApplications,
        IntPtr rgApplications, // not used
        uint nServices,
        IntPtr rgsServiceNames // not used
    );

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmGetList(
        int dwSessionHandle,
        out uint pnProcInfoNeeded,
        ref uint pnProcInfo,
        [In, Out] RM_PROCESS_INFO[] rgAffectedApps,
        out uint lpdwRebootReasons
    );

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmShutdown(
        int dwSessionHandle,
        uint lActionFlags,
        IntPtr fnStatus // callback not used
    );

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmRestart(
        int dwSessionHandle,
        uint lActionFlags,
        IntPtr fnStatus // callback not used
    );

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    public static extern int RmEndSession(int dwSessionHandle);
}
"@ -ErrorAction Stop

function Restart-Explorer {
    # Constants
    $RM_SESSION_KEY_LEN = 32

    # Prepare session
    $sessionHandle = 0
    $sessionKey = New-Object System.Text.StringBuilder ($RM_SESSION_KEY_LEN + 1)

    # Start session
    $start = [RestartManager]::RmStartSession([ref]$sessionHandle, 0, $sessionKey)
    if ($start -ne 0) {
        throw "RmStartSession failed with error code $start"
    }

    try {
        # Register explorer.exe by full path
        $explorerPath = Join-Path $env:WINDIR 'explorer.exe'
        $files = @($explorerPath)

        $reg = [RestartManager]::RmRegisterResources(
            $sessionHandle, [uint32]$files.Count, $files, 0, [IntPtr]::Zero, 0, [IntPtr]::Zero
        )
        if ($reg -ne 0) {
            throw "RmRegisterResources failed with error code $reg"
        }

        $needed = 0
        $count = 0
        $reasons = 0
        
        # First call to get required size
        $result = [RestartManager]::RmGetList($handle, [ref]$needed, [ref]$count, $null, [ref]$reasons)
        
        if ($result -eq 234) { # 234 == ERROR_MORE_DATA
            $array = New-Object RM_PROCESS_INFO[] $needed
            $count = $needed
            $result = [RestartManager]::RmGetList($handle, [ref]$needed, [ref]$count, $array, [ref]$reasons)
        
            if ($result -eq 0) {
                Write-Host "Porcesses using Explorer.exe"
                foreach ($proc in $array) {
                    Write-Host "Process: $($proc.strAppName) (PID=$($proc.Process.dwProcessId))"
                }
            }
        }

        # Request shutdown of explorer (no special flags)
        $sh = [RestartManager]::RmShutdown($sessionHandle, 0, [IntPtr]::Zero)
        if ($sh -ne 0) {
            throw "RmShutdown failed with error code $sh"
        }

        Start-Sleep -Milliseconds 500

        # Request restart of explorer
        $rs = [RestartManager]::RmRestart($sessionHandle, 0, [IntPtr]::Zero)
        if ($rs -ne 0) {
            throw "RmRestart failed with error code $rs"
        }

        Write-Host "Explorer restarted via Restart Manager. SessionKey=$($sessionKey.ToString())"
    } finally {
        # End session
        [void][RestartManager]::RmEndSession($sessionHandle)
    }
}

# Execute
Restart-Explorer