Useful synchronization MACROs for multithreaded applications

[Kev Peel]

'______________________________________________________________________________
'
'  WorkerThread Example
'
'  Spawns a second "worker" thread and demonstrates synchronizing variables
'  between each thread using a critical section object and a couple of MACROs.
'
'  Posted By Kev Peel ([URL="http://www.kgpsoftware.com"]www.kgpsoftware.com[/URL]), Dec 2007.
'______________________________________________________________________________
#Compile Exe
#Dim All
#Register None
%USEMACROS = 1                      ' Cuts code size.
#Include "WIN32API.INC"             ' Includes required API definitions.
Global gCS As CRITICAL_SECTION      ' Thread synchronization object.
Global gnEndApp As Long             ' Set to TRUE to exit the application.

'------------------------------------------------------------------------------
' Safely reads any variable type to a temporary variable and returns it.
' This function uses the global critical section variable.
'------------------------------------------------------------------------------
Macro Function SafeReadVar(vVar, vType)
  MacroTemp vTmp
  Local vTmp As vType
  EnterCriticalSection gCS
  vTmp = vVar
  LeaveCriticalSection gCS
End Macro = vTmp

'------------------------------------------------------------------------------
' Safely writes any value to the specified variable.
' This function uses the global critical section variable.
'------------------------------------------------------------------------------
Macro SafeWriteVar(vVar, vValue)
  EnterCriticalSection gCS
  vVar = vValue
  LeaveCriticalSection gCS
End Macro

'------------------------------------------------------------------------------
' Sample "worker thread" Does background stuff.
'------------------------------------------------------------------------------
Function WorkerThread(ByVal dummy As Long) As Long
  Do
     If MessageBox(%HWND_DESKTOP, "Close the app?", "WorkerThread Example", %MB_OKCANCEL Or %MB_ICONINFORMATION) = %IDOK Then
        ' Safely assign the flag...
        SafeWriteVar(gnEndApp, %TRUE)
        ' End the thread...
        Exit Function
     End If
  Loop
  
End Function
 
'------------------------------------------------------------------------------
' Creates a worker thread and enters a sample message loop.
'------------------------------------------------------------------------------
Function PBMain
  Local dummy As Long
  gnEndApp = %FALSE
  InitializeCriticalSection gCS
  ' Spawn worker thread...
  Thread Create WorkerThread(0) To dummy
  ' Sample message loop...
  Do Until SafeReadVar(gnEndApp, Long) <> %FALSE
     Dialog DoEvents
  Loop
  DeleteCriticalSection gCS
End Function