DÉCOURVIR LES "BACKGROUND IO PRIORITY" DE VISTA

Imports System.Runtime.InteropServices

''' <summary>
''' Classe fournissant des méthodes permettant changer les priorités IO pour le process et thread courant.
''' </summary>
''' <remarks>Vista ou 2008 Server requit.</remarks>
Public Class IOPriority

    Const THREAD_MODE_BACKGROUND_BEGIN As Integer = &H10000
    Const THREAD_MODE_BACKGROUND_END As Integer = &H20000
    Const PROCESS_MODE_BACKGROUND_BEGIN As Integer = &H100000
    Const PROCESS_MODE_BACKGROUND_END As Integer = &H200000

    Public Const ERROR_THREAD_MODE_ALREADY_BACKGROUND As Integer = &H400
    Public Const ERROR_THREAD_MODE_NOT_BACKGROUND As Integer = &H401
    Public Const ERROR_PROCESS_MODE_ALREADY_BACKGROUND As Integer = &H402
    Public Const ERROR_PROCESS_MODE_NOT_BACKGROUND As Integer = &H403
    Public Const ERROR_FAILED_TO_ENTER_BACKGROUND_MODE As Integer = -1


    ''' <summary>
    ''' Indique si le thread courant est en priorité faible sur les IO.
    ''' </summary>
    ''' <returns><b>True</b> si priorité faible.<b>False</b> sinon.</returns>
    Public Shared Function IsThreadBackgroundMode() As Integer

        Dim iret As Integer = False

        Dim bIOBckMode As Boolean = SetThreadBackgroundMode(True)

        If (bIOBckMode) Then
            SetThreadBackgroundMode(False)
            iret = ERROR_THREAD_MODE_NOT_BACKGROUND
        Else

            If Marshal.GetLastWin32Error() = ERROR_THREAD_MODE_ALREADY_BACKGROUND Then
                iret = ERROR_THREAD_MODE_ALREADY_BACKGROUND
            Else
                iret = ERROR_FAILED_TO_ENTER_BACKGROUND_MODE
            End If

        End If

        Return iret

    End Function

    ''' <summary>
    ''' Indique si le process courant est en priorité faible sur les IO.
    ''' </summary>
    ''' <returns><b>True</b> si priorité faible.<b>False</b> sinon.</returns>
    Public Shared Function IsProcessBackgroundMode() As Integer

        Dim iret As Integer = False

        Dim bIOBckMode As Boolean = SetProcessBackgroundMode(True)

        If (bIOBckMode) Then
            SetProcessBackgroundMode(False)
            iret = ERROR_PROCESS_MODE_NOT_BACKGROUND
        Else

            If Marshal.GetLastWin32Error() = ERROR_PROCESS_MODE_ALREADY_BACKGROUND Then
                iret = ERROR_PROCESS_MODE_ALREADY_BACKGROUND
            Else
                iret = ERROR_FAILED_TO_ENTER_BACKGROUND_MODE
            End If

        End If

        Return iret

    End Function

    ''' <summary>
    ''' Définit la priorité du process courant sur les IO.
    ''' </summary>
    ''' <param name="enable"><b>True</b> pour passer le process en priorité faible sur les IO. <b>False</b> pour restaurer une priorité normal sur les IO.</param>
    ''' <returns><b>True</b> si changement réussi.<b>False</b> en cas d'échec.</returns>
    Public Shared Function SetProcessBackgroundMode(ByVal enable As Boolean) As Boolean

        If CheckOsVersion() Then

            Dim bret As Boolean = False
            Dim hProcess As IntPtr = Process.GetCurrentProcess().Handle

            If enable Then
                bret = NativeMethods.SetPriorityClass(hProcess, PROCESS_MODE_BACKGROUND_BEGIN)
            Else
                bret = NativeMethods.SetPriorityClass(hProcess, PROCESS_MODE_BACKGROUND_END)
            End If

            Return bret

        Else

            Throw New Exception("Not supported by this Windows version.")

        End If

    End Function

    ''' <summary>
    ''' Définit la priorité du thread courant sur les IO.
    ''' </summary>
    ''' <param name="enable"><b>True</b> pour passer le thread en priorité faible sur les IO. <b>False</b> pour restaurer une priorité normal sur les IO.</param>
    ''' <returns><b>True</b> si changement réussi.<b>False</b> en cas d'échec.</returns>
    Public Shared Function SetThreadBackgroundMode(ByVal enable As Boolean) As Boolean

        If CheckOsVersion() Then

            Dim bret As Boolean = False
            Dim hThread As IntPtr = IntPtr.Zero

            Try

                hThread = ThreadHelper.GetCurentThread()

                If enable Then
                    bret = NativeMethods.SetThreadPriority(hThread, THREAD_MODE_BACKGROUND_BEGIN)
                Else
                    bret = NativeMethods.SetThreadPriority(hThread, THREAD_MODE_BACKGROUND_END)
                End If

            Catch ex As Exception

            Finally
                ThreadHelper.CloseHandle(hThread)
            End Try

            Return bret

        Else

            Throw New Exception("Not supported by this Windows version.")

        End If

    End Function

    ''' <summary>
    ''' Vérifie la version de Windows (Vista ou 2008 Server).
    ''' </summary>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Shared Function CheckOsVersion() As Boolean

        If Environment.OSVersion.Version.Major >= 6 Then
            Return True
        Else
            Return False
        End If

    End Function

End Class