title: Reader-writer lock with condition variable
body: <p>I find neither boost nor tbb library's condition variable has the interface of working with reader-writer lock (ie. shared mutex in boost). condition_variable::wait() only accepts mutex lock. But I think it's quite reasonable to have it work with reader-writer lock. Can anyone tell me the reason why they don't support that, or why people don't do that?</p>
  
  <p>Thanks,
  Cui</p>