For my USB Disk Ejector program:
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I`m catching windows messages related to drive addition/removal. When I get the messages that a drive has been added or removed I rescan all drives and repopulate my list of usb drives.
However sometimes another drive might be added/removed when I'm rescanning all the drives - so I need to scan the drives again.

This is perfectly fine, but what I do now is bad - I have a global variable that I increment each time I get the "DrivesHaveChanged" message. I have a thread that rescans the drives but this thread also writes to the global variable too.

Help me please:
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This is essentially a threading problem. I'm writing to a global variable from within my main thread and a child thread - I know this is bad.

Any ideas on how I fix this? A critical section is apparently one solution?


At the moment I do this:
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Pseudo-pascal code:


fChangeMessageCount: global variable - integer

procedure CatchTheMessages
begin
 if ItsTheMessageIWant then
 begin
   inc(fChangeMessageCount); //increment it
   if EventsThread.Suspended then EventsThread.Resume;
 end;
end


procedure TEventsThread.Execute;
begin
  while not terminated do
  begin
    if self.Terminated then break;

    if (fChangeMessageCount > 0) and (fEjector.Busy = false) then
    begin
      sleep(500);  //gives extra time for devices with multi volumes/partitions
      fChangeMessageCount:=0; //set it back to 0 because we're about to scan
      RescanAllDrives;
    end
    else
      self.Suspend;
  end;
end;