9.7 Guard Classes Without Templates

If your compiler doesn't support templates, or your application can't use them, applying the guard class becomes more difficult, but not impossible. You must provide a class that can be locked for each object. For instance, to support RWDBConnection, you must provide the following class:

class GuardRWDBConnection {
    RWDBConnection& conn;
  public:
    GuardRWDBConnection(const RWDBConnection& conn)
      : conn_((RWDBConnection&)conn) { conn_.acquire(); }
    ~GuardRWDBConnection()
      { conn_.release(); }
};

This class can be used like the previous template version. Compare that code with the next example:

void doSomething(const RWDBConnection& conn)
{
  // We're going to use the connection so we'd better 
  // control access
  GuardRWDBConnection guard(conn);   // RWDBConnection supports the
                                     // necessary interface.
  // Do something on the connection.

  // The mutex is released when the Guard instance goes out of
  // scope. 
}