Can I nest critical sections? Is TCriticalSection nestable?

Question

I want to have two procedures which can call each other, or be called from whatever threads are running, but only have one running at a time. How can I do this? Will this work correctly?

var
  cs: TCriticalSection;

procedure a;
begin
  cs.Acquire;
  try
    // Execute single threaded here. 
  finally
    cs.Release;
  end;
end;

procedure b;
begin
  cs.Acquire;
  try
    // Execute single threaded here. Maybe with calls to procedure a.
  finally
    cs.Release;
  end;
end;

Answer 1

Yes, that will work. Procedure A can call B and vice versa within the same thread and while Thread A is using procedure A or B, Thread B has to wait when it wants to use those procedures.

See the MSDN documentation about Critical Sections: http://msdn.microsoft.com/en-us/library/ms682530%28VS.85%29.aspx

Critical sections can be nested, but for every call to Acquire you must have a call to Release. Because you have your Release call in a try .. finally clause you ensure that this happens, so your code is fine.