7920393a   
   From: cristom@charter.net   
      
   "Mathias Gaunard"  wrote in message   
   news:0f960bb1-ebad-4dc6-9b33-17d9e701946c@h5g2000vbf.googlegroups.com...   
   > On Oct 24, 6:46 pm, Alexander Terekhov  wrote:   
   >   
   >> I always thought that C++11 mutex locks can be expressed in terms of   
   >> relaxed C++11 atomic<> operations and acquire/release fences (not the   
   >> same as memory_order_seq_cst fence).   
   >   
   > AFAIK, locking a mutex is a full barrier, not just an acquire barrier.   
   > This is not the case for spinlocks though.   
   >   
   > Sure, you can do a a full barrier by doing an acquire followed by a   
   > release, but it's possibly more efficient to just do the full barrier.   
   >   
   >   
   >> class swap_based_mutex_for_windows { // noncopyable   
   >>   
   >>   atomic m_lock_status; // 0: free, 1/-1: locked/contention   
   >>   auto_reset_event m_retry_event; // slow binary semaphore (windows)   
   >   
   > How is that pseudo-code written only using built-in atomic operations   
   > when there is a reference to a heavyweight kernel-level   
   > synchronization mechanism?   
      
   Perhaps something like:   
      
      
      
   _____________________________________________   
   struct auto_reset_event   
   {   
       std::mutex m_mutex;   
       std::condition_variable m_cond;   
       bool m_state;   
      
      
       auto_reset_event() : m_state(false) {}   
       auto_reset_event(bool state) : m_state(state) {}   
      
      
       void set()   
       {   
           m_mutex.lock();   
           m_state = true;   
           lock.unlock();   
           m_cond.notify_one();   
       }   
      
       void wait()   
       {   
           std::unique_lock lock(m_mutex);   
           while (! m_state) m_cond.wait(lock);   
           m_state = false;   
       }   
   };   
   _____________________________________________   
      
      
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