sync-barrier.hpp

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/*
  SYNC-BARRIER.hpp  -  N-fold synchronisation point with yield-wait
 
   Copyright (C)
     2023,            Hermann Vosseler <Ichthyostega@web.de>
 
 **Lumiera** is free software; you can redistribute it and/or modify it
 under the terms of the GNU General Public License as published by the
 Free Software Foundation; either version 2 of the License, or (at your
 option) any later version. See the file COPYING for further details.
 
*/
 
 
#ifndef LIB_SYNC_BARRIER_H
#define LIB_SYNC_BARRIER_H
 
 
#include "lib/error.hpp"
#include "lib/nocopy.hpp"
 
#include <thread>
#include <atomic>
 
 
namespace lib {
  
  
  class SyncBarrier
    : util::NonCopyable
    {
      std::atomic_int latch_;
      
    public:
      explicit
      SyncBarrier (uint nFold =2)
        : latch_{int(nFold)}
        {
          REQUIRE (nFold >= 2, "Pointless to sync less than two participants.");
          ENSURE  (nFold < 100'000, "Danger territory.... sync 100k Threads??");
        }
      
      void
      sync()
        {
          size_t level = latch_.fetch_add(-1, std::memory_order_acq_rel);
          if (1 < level)
            do std::this_thread::yield();
            while (0 < latch_.load (std::memory_order_relaxed));
          else
            latch_.store (0, std::memory_order_relaxed);
        }             //  prevent spurious calls from wrapping
    };
  
  
  
} // namespace lib
#endif /*LIB_SYNC_BARRIER_H*/