Microsoft KB Archive/231298

= How To Use SetWaitableTimer With Visual Basic =

Article ID: 231298

Article Last Modified on 7/13/2004

-

APPLIES TO


 * Microsoft Visual Basic 5.0 Learning Edition
 * Microsoft Visual Basic 6.0 Learning Edition
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition
 * Microsoft Visual Basic 4.0 Professional Edition

-



This article was previously published under Q231298



SUMMARY
Many programmers use the Sleep API function to pause the execution of their programs. One of the disadvantages of using Sleep is that it pauses the thread that the application is running in, and that any window that the application has open will not repaint properly. This may present an unattractive user interface to the user. An alternative to Sleep is to use SetWaitableTimer, which will allow the screen to repaint, receive DDE messages, and so forth.



MORE INFORMATION
The following code sample illustrates the use of the SetWaitableTimer API.

Step-by-Step Example
 Start a new Standard EXE project in Visual Basic. Form1 is created by default. Place two CommandButtons on Form1.  Paste the following code into the code module of Form1: Option Explicit

' Sleep API is declared in the form to keep the ' SetWaitableTimer code in its own re-usable module. Private Declare Sub Sleep Lib "kernel32" ( _   ByVal dwMilliseconds As Long)

Private Sub Command1_Click Command1.Enabled = False Wait 10 ' seconds Command1.Enabled = True End Sub

Private Sub Command2_Click Command2.Enabled = False Sleep 10000 ' milliseconds Command2.Enabled = True End Sub

Private Sub Form_Load With Form1 .Height = 1400 .Width = 2400 End With With Command1 .Move 100, 100, 2000, 300 .Caption = "SetWaitableTimer" End With With Command2 .Move 100, 500, 2000, 300 .Caption = "Sleep" End With End Sub  From the Project menu, click Add Module to add a new module (Module1) to the project.  Paste the following code into Module1: 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 Long) 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 ft.dwHighDateTime = ft.dwHighDateTime + 1 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  Run the project. Click the Sleep button. While the application is sleeping, notice that the screen does not repaint (drag another window over top of the application, and then drag it away). Then, try the same test with the SetWaitableTimer button.</li></ol>

<div class="references_section">