vb.net - Test while running two functions at the same time -

i running these 2 simple functions using background workers, (write test file) , (read text file) shouldn't give errors getting these exceptions

a first chance exception of type 'system.io.ioexception' occurred in mscorlib.dll

any idea how prevent that?

option explicit on option strict on  public class form1      dim istring string     dim worker1 boolean = false     dim worker2 boolean = false      private sub button2_click(byval sender system.object, byval e system.eventargs) handles button2.click         timer1.enabled = true     end sub      private sub timer1_tick(sender object, e eventargs) handles timer1.tick         try             if worker1 = false                 worker1 = true                 backgroundworker1.runworkerasync()             end if              if worker2 = false                 worker2 = true                 backgroundworker2.runworkerasync()             end if         catch ex exception             debug.print("timer1_tick error:" & date.now & ex.message)         end try     end sub       private sub backgroundworker1_dowork(byval sender system.object, byval e system.componentmodel.doworkeventargs) handles backgroundworker1.dowork         call writedatatofile(date.now.tostring("h:mm:ss tt - fff"), "test.txt")     end sub      private sub backgroundworker2_dowork(byval sender system.object, byval e system.componentmodel.doworkeventargs) handles backgroundworker2.dowork         istring = gettextdatacontents("test.txt")     end sub      private sub backgroundworker1_complete(byval sender system.object, byval e system.componentmodel.runworkercompletedeventargs) handles backgroundworker1.runworkercompleted         worker1 = false     end sub      private sub backgroundworker2_complete(byval sender system.object, byval e system.componentmodel.runworkercompletedeventargs) handles backgroundworker2.runworkercompleted         worker2 = false         label1.text = istring     end sub       public sub writedatatofile(byval strdata string, byval strfile string, optional byval fullpath boolean = false)         if fullpath = false strfile = system.appdomain.currentdomain.basedirectory & strfile          dim notinuse = true         while notinuse             try                 using objwriter new system.io.streamwriter(strfile, false)                     objwriter.write(strdata)                     objwriter.close()                     notinuse = false                 end using             catch ex exception                 debug.print("writedatatofile error:" & date.now & ex.message)                 system.threading.thread.sleep(1)             end try         end while     end sub       function gettextdatacontents(byval strfile string, optional byval fullpath boolean = false) string         gettextdatacontents = nothing         if fullpath = false strfile = system.appdomain.currentdomain.basedirectory & strfile          dim notinuse = true         while notinuse             try                 dim strcontents string                 dim objreader system.io.streamreader                  objreader = new system.io.streamreader(strfile, true)                 strcontents = objreader.readtoend()                 objreader.close()                  notinuse = false                 return strcontents             catch ex exception                 debug.print(date.now & " gettextdatacontents error " & ex.message)                 system.threading.thread.sleep(1)             end try         end while     end function   end class 

the file may locked editing while writing it.

see article more details - http://msdn.microsoft.com/en-us/library/vstudio/kztecsys%28v=vs.100%29.aspx