Re: [Boost-bugs] [Boost C++ Libraries] #1850: request for unlock_guard (and/or unique_unlock) to compliment lock_guard/unique_lock

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #1850: request for unlock_guard (and/or unique_unlock) to compliment lock_guard/unique_lock
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-03-21 20:52:22

#1850: request for unlock_guard (and/or unique_unlock) to compliment
lock_guard/unique_lock
--------------------------------+-------------------------------------------
  Reporter:  bgreen0@…          |       Owner:  viboes                    
      Type:  Feature Requests   |      Status:  assigned                  
 Milestone:  Boost 1.36.0       |   Component:  thread                    
   Version:  Boost 1.35.0       |    Severity:  Not Applicable            
Resolution:                     |    Keywords:  unlock_guard release_guard
--------------------------------+-------------------------------------------

Comment (by viboes):

 I'm wondering if this features is not dangerous combined with other lock
 guards. E.g. The user of lock_guard expects his lock to be locked during
 his lifetime, so nesting a unlock_guard will break the user expectations.
 I think that as far as we unlock we are transferring ownership, so the
 safe way to nest the unlock guard is to use move semantics from a lock
 owning the mutex. What do you think of a reverse_lock

 {{{
     template<typename Lock>
     class reverse_lock
     {
     private:
         Lock& m;

     public:
         reverse_lock(reverse_lock const&) = delete;
         reverse_lock& operator=(reverse_lock const&) = delete;

         typedef typename Lock::mutex_type mutex_type;
         explicit reverse_lock(Lock& m_):
             m(m_)
         {
             BOOST_ASSERT(m.owns_lock());
             m.unlock();
         }
         reverse_lock(Lock& m_,adopt_unlock_t):
             m(m_)
         {
             BOOST_ASSERT(!m.owns_lock());
         }
         ~reverse_lock()
         {
             if(!m.owns_lock())
                 m.lock();
         }
         explicit operator bool() const BOOST_NOEXCEPT
         {
             return m.owns_lock(); // always false
         }
         bool owns_lock() const BOOST_NOEXCEPT
         {
             return m.owns_lock(); // always false
         }

         mutex_type* mutex() const BOOST_NOEXCEPT
         {
             return m.mutex();
         }

         mutex_type* release() BOOST_NOEXCEPT
         {
           return m.release();
         }
     };
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/1850#comment:4>
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