title: Boost - shared_mutex has to be same instance?
body: <p>I want to use shared_mutex with shared/unique locks for read/write.</p>
  
  <p>Now if I have 2 objects and i want them to use the same lock, can I assign the value of the first mutex to the second mutex ?<br>
  Or do I have to work create a pointer to the shared_mutex and then have them both point to the same object instance?</p>
  
  <p>I mean, will this work correctly, and both objects will work on same lock ?:</p>
  
  <pre><code>typedef boost::shared_mutex ReadWriteMutex;
      class A {
      ReadWriteMutex lock;
  }
  
  void test() {
      A a = new A();
      B b = new B()
      b.lock = a.lock;
  }
  </code></pre>