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Better Than VB DoEvents


Visual Basic 6, or VB Classic

Doevents in VB utilizes a lot of Windows resources. Use it in a Do-While loop and watch the resource meter on your computer go over the edge! This code I call 'Wait' eleviates this resource intesive task and allows Windows to do it's timeslicing to handle other events.

Original Author: Steve H. Miller

Inputs

To use it, simply cut-and-paste the code into a module (.BAS) and make a call to the 'Wait' event as such:
Call Wait 5 ' Wait for 5 seconds

Assumptions

Just plop the whole thing into a .BAS module and call the function passing the number of seconds as a parameter to wait.

Returns

Returns nothing.

Side Effects

Reduced resource usage!

Code

Option Explicit
    Private Type FILETIME
      dwLowDateTime As Long
      dwHighDateTime As Long
    End Type
    Private Const WAIT_ABANDONED& = &H80&
    Private Const WAIT_ABANDONED_0& = &H80&
    Private Const WAIT_FAILED& = -1&
    Private Const WAIT_IO_COMPLETION& = &HC0&
    Private Const WAIT_OBJECT_0& = 0
    Private Const WAIT_OBJECT_1& = 1
    Private Const WAIT_TIMEOUT& = &H102&
    Private Const INFINITE = &HFFFF
    Private Const ERROR_ALREADY_EXISTS = 183&
    Private Const QS_HOTKEY& = &H80
    Private Const QS_KEY& = &H1
    Private Const QS_MOUSEBUTTON& = &H4
    Private Const QS_MOUSEMOVE& = &H2
    Private Const QS_PAINT& = &H20
    Private Const QS_POSTMESSAGE& = &H8
    Private Const QS_SENDMESSAGE& = &H40
    Private Const QS_TIMER& = &H10
    Private Const QS_MOUSE& = (QS_MOUSEMOVE _
                  Or QS_MOUSEBUTTON)
    Private Const QS_INPUT& = (QS_MOUSE _
                  Or QS_KEY)
    Private Const QS_ALLEVENTS& = (QS_INPUT _
                  Or QS_POSTMESSAGE _
                  Or QS_TIMER _
                  Or QS_PAINT _
                  Or QS_HOTKEY)
    Private Const QS_ALLINPUT& = (QS_SENDMESSAGE _
                  Or QS_PAINT _
                  Or QS_TIMER _
                  Or QS_POSTMESSAGE _
                  Or QS_MOUSEBUTTON _
                  Or QS_MOUSEMOVE _
                  Or QS_HOTKEY _
                  Or QS_KEY)
    Private Declare Function CreateWaitableTimer Lib "kernel32" _
      Alias "CreateWaitableTimerA" ( _
      ByVal lpSemaphoreAttributes As Long, _
      ByVal bManualReset As Long, _
      ByVal lpName As String) As Long
      
    Private Declare Function OpenWaitableTimer Lib "kernel32" _
      Alias "OpenWaitableTimerA" ( _
      ByVal dwDesiredAccess As Long, _
      ByVal bInheritHandle As Long, _
      ByVal lpName As String) As Long
      
    Private Declare Function SetWaitableTimer Lib "kernel32" ( _
      ByVal hTimer As Long, _
      lpDueTime As FILETIME, _
      ByVal lPeriod As Long, _
      ByVal pfnCompletionRoutine As Long, _
      ByVal lpArgToCompletionRoutine As Long, _
      ByVal fResume As Long) As Long
      
    Private Declare Function CancelWaitableTimer Lib "kernel32" ( _
      ByVal hTimer As Long)
      
    Private Declare Function CloseHandle Lib "kernel32" ( _
      ByVal hObject As Long) As Long
      
    Private Declare Function WaitForSingleObject Lib "kernel32" ( _
      ByVal hHandle As Long, _
      ByVal dwMilliseconds As Long) As Long
      
    Private Declare Function MsgWaitForMultipleObjects Lib "user32" ( _
      ByVal nCount As Long, _
      pHandles As Long, _
      ByVal fWaitAll As Long, _
      ByVal dwMilliseconds As Long, _
      ByVal dwWakeMask As Long) As Long
    Public Sub Wait(lNumberOfSeconds As Double)
      Dim ft As FILETIME
      Dim lBusy As Long
      Dim lRet As Long
      Dim dblDelay As Double
      Dim dblDelayLow As Double
      Dim dblUnits As Double
      Dim hTimer As Long
      
      hTimer = CreateWaitableTimer(0, True, App.EXEName & "Timer")
      
      If Err.LastDllError = ERROR_ALREADY_EXISTS Then
        ' If the timer already exists, it does not hurt to open it
        ' as long as the person who is trying to open it has the
        ' proper access rights.
      Else
        ft.dwLowDateTime = -1
        ft.dwHighDateTime = -1
        lRet = SetWaitableTimer(hTimer, ft, 0, 0, 0, 0)
      End If
      
      ' Convert the Units to nanoseconds.
      dblUnits = CDbl(&H10000) * CDbl(&H10000)
      dblDelay = CDbl(lNumberOfSeconds) * 1000 * 10000
      
      ' By setting the high/low time to a negative number, it tells
      ' the Wait (in SetWaitableTimer) to use an offset time as
      ' opposed to a hardcoded time. If it were positive, it would
      ' try to convert the value to GMT.
      ft.dwHighDateTime = -CLng(dblDelay / dblUnits) - 1
      dblDelayLow = -dblUnits * (dblDelay / dblUnits - _
        Fix(dblDelay / dblUnits))
      
      If dblDelayLow < CDbl(&H80000000) Then
        ' &H80000000 is MAX_LONG, so you are just making sure
        ' that you don't overflow when you try to stick it into
        ' the FILETIME structure.
        dblDelayLow = dblUnits + dblDelayLow
      End If
      
      ft.dwLowDateTime = CLng(dblDelayLow)
      lRet = SetWaitableTimer(hTimer, ft, 0, 0, 0, False)
      
      Do
        ' QS_ALLINPUT means that MsgWaitForMultipleObjects will
        ' return every time the thread in which it is running gets
        ' a message. If you wanted to handle messages in here you could,
        ' but by calling Doevents you are letting DefWindowProc
        ' do its normal windows message handling---Like DDE, etc.
        lBusy = MsgWaitForMultipleObjects(1, hTimer, False, _
          INFINITE, QS_ALLINPUT&)
        DoEvents
      Loop Until lBusy = WAIT_OBJECT_0
      
      ' Close the handles when you are done with them.
      CloseHandle hTimer
    End Sub

About this post

Posted: 2003-06-01
By: ArchiveBot
Viewed: 149 times

Categories

Visual Basic 6

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