TCriticalSection TryEnter Method Always Returns True

Question

When calling the TryEnter method on a TCriticalSection the result is always true. Surely this should only return true if it is able to aquire the lock?

var
  MyCritSect: TCriticalSection;

begin
  MyCritSect := TCriticalSection.Create;
  try
    //    MyCritSect.Enter;
    Writeln(BoolToStr(MyCritSect.TryEnter, True)); // This should return True
    Writeln(BoolToStr(MyCritSect.TryEnter, True)); // This should return False?
    Readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Even if you uncomment the MyCritSect.Enter; line it still returns True for both calls to TryEnter.

I am using Delphi XE and Windows 10.

Answer 1

Critical sections are re-entrant locks. From the documentation:

When a thread owns a critical section, it can make additional calls to EnterCriticalSection or TryEnterCriticalSection without blocking its execution. This prevents a thread from deadlocking itself while waiting for a critical section that it already owns.

Your call to TryEnter will fail if made from a different thread, and the first thread already owns the lock.