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Locking Functions due to Multi-Threading in Visual Basic 6 Possible?

Posted on 2003-03-05
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Last Modified: 2013-11-25
Is theere a way to lock a function (or rather, a selection of code) from being executed by more than 1 thread.  I noticed there was a SyncLock command in VB .NET but this does not exist for VB6.  Can someone give me the deatails so i can implement the same kind of feature.
If it is of importance i am calling a function that writes out to a file.  The problem is that there are many threads running that could call this same function to write out to the file (append to it).  Since i could actually be writing to the file before i am interrupted by another thread which causes it to begin writing you can see it can end up being a mess without the lock feature

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Question by:aniston
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Mikal613 earned 80 total points
ID: 8071745
how about CreateMutex or Semaphore you can create a "Lock" on a thread untill the process ended.

Declare Function CreateMutex Lib "kernel32" Alias "CreateMutexA" (lpMutexAttributes As SECURITY_ATTRIBUTES, ByVal bInitialOwner As Long, ByVal lpName As String) As Long

Example.
Private Declare Function ReleaseMutex Lib "kernel32" (ByVal hMutex As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Sub Form_Load()
    Dim hMutex As Long
    'Try to create a new Mutex
    hMutex = CreateMutex(ByVal 0&, 1, App.Title)
    'Did the mutex already exist?
    If (Err.LastDllError = ERROR_ALREADY_EXISTS) Then

        'Then Dont write to the file.-----

        ReleaseMutex hMutex
        CloseHandle hMutex
          exit sub
    Else
        Write to the File
    End If
End Sub
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