title: Regarding shared_ptr reference count block
body: <p>I had 2 questions regarding the <code>std::shared_ptr</code> control block:</p>
  
  <p>(1) <strong>Regarding size</strong>:
  How can I <em>programatically</em> find the exact size of the control block for a <code>std::shared_ptr</code>?</p>
  
  <p>(2) <strong>Regarding logic</strong>:
  Additionally, <code>boost::shared_ptr</code> mentions that they are completely lock-free with respect to changes in the control block.(<em>Starting with Boost release 1.33.0, <code>shared_ptr</code> uses a lock-free implementation on most common platforms.</em>) I don't think <code>std::shared_ptr</code> follows the same - is this planned for any future C++ version? Doesn't this also mean that <code>boost::shared_ptr</code> is a better idea for multithreaded cases?</p>