How to sleep a process until an event happen.

[Sebastian Zich]

I’m working on a project for the University, on process synchronization and I need to sleep a process until an event happen.
I did something like this but it didn’t work

Dim A as Boolean
----------------------
Sub Wait ()
A= false
While not(A)
doevents
Wend
EndSub
----------------------
Sub Signal()
A= true
EndSub

Thank you very much

Sebastian

[KenX]

i did basically the same code as
you have above and it worked...
i am not sure but i think it would
depend on what events you connected
them to...

Dim A As Boolean

Private Sub Command1_Click()
    A = False
    While Not (A)
        DoEvents
    Wend
    MsgBox "Hello!"
End Sub

Private Sub Command2_Click()
    A = True
End Sub

[SonGouki]

What kind of "event" do you need to wait for?

If what you need is to wait for an app to finish loading or until an app has been closed you could try this:

Wait until an app is loaded

Private Const SYNCHRONIZE As Long = &H100000
Private Const INFINITE As Long = &HFFFF

Private Declare Function WaitForInputIdle _
                Lib "user32" _
                (ByVal hProcess As Long, ByVal dwMilliseconds As Long) As Long

Private Declare Function CloseHandle _
                Lib "kernel32" _
                (ByVal hObject As Long) As Long

Private Declare Function OpenProcess _
                Lib "kernel32" _
                (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
                ByVal dwProcessId As Long) As Long

Private Sub cmdRunApp_Click()
   Dim hProcessID As Long
   Dim hProcess As Long
   Dim sShellPath As String
   
   sShellPath = "C:\WINDOWS\NOTEPAD.EXE"
   
   hProcessID = Shell(sShellPath, vbNormalFocus)
   
   If hProcessID <> 0 Then
      hProcess = apiOpenProcess(SYNCHRONIZE, 0, vhProcID)
      
      If hProcess <> 0 Then
         Call apiWaitForInputIdle(hProcess, INFINITE)
         Call apiCloseHandle(hProcess)
      End If
   
   End If

End Sub

Wait until an app is closed

Private Const SYNCHRONIZE As Long = &H100000
Private Const INFINITE As Long = &HFFFF


Private Declare Function WaitForSingleObject _
                Lib "kernel32" _
                (ByVal hHandle As Long, ByVal dwMilliseconds As Long) As Long

Private Declare Function CloseHandle _
                Lib "kernel32" _
                (ByVal hObject As Long) As Long

Private Declare Function OpenProcess _
                Lib "kernel32" _
                (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
                ByVal dwProcessId As Long) As Long

Private Sub cmdRunApp_Click()
   Dim hProcessID As Long
   Dim hProcess As Long
   Dim sShellPath As String
   
   sShellPath = "C:\WINDOWS\NOTEPAD.EXE"
   
   hProcessID = Shell(sShellPath, vbNormalFocus)
   
   If hProcessID <> 0 Then
      hProcess = apiOpenProcess(SYNCHRONIZE, 0, vhProcID)
      
      If hProcess <> 0 Then
         Call Me.Hide
         App.TaskVisible = False
         Call apiWaitForSingleObject(hProcess, INFINITE)
         Call apiCloseHandle(hProcess)
         App.TaskVisible = True
         Call Me.Show
      End If
   
   End If

End Sub

To put an app to sleep

Private Declare Sub Sleep Lib "kernel32" Alias "Sleep" (ByVal dwMilliseconds As Long)

Just specify the number of seconds you want the app to wait in the dwMilliseconds parameter.

Et Voila!
Hope it helps.

[SonGouki]

Oops! A copy and paste mistake.

Change vhProcID to hProcessID in the first two examples.

Sorry if it caused any confusion.


PS.
Anybody know why I can't Edit a response anymore?

[Sebastian Zich]

Thank you very much for your help.
It is not for running an application, its a Buffer class, that use a Monitor to solve Producer and Consumer problem, and the Monitor use a Semaphores for synchronisation, and the Semaphores use the Signal and Wait functions,
So when consumer ask for data to the Buffer it call the Semaphores and it call a Wait if the buffer is empty, and when the producer put data in de buffer it calls the Semaphores and it call Signal that wake up all the cascade process.
The problem is that it works with, a single Producer, single Consumer but it didn't work when you have some many instances of the buffer, Ex : The first instance of the SignalWait class is stopped forever by the second instance of it.

Thank you very much for your help, again.

Sebastian