atomic_bounded_decrement.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
/*
 * Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration.
 */
#ifndef CXXUTILS_ATOMIC_BOUNDED_DECREMENT_H
#define CXXUTILS_ATOMIC_BOUNDED_DECREMENT_H
 
 
#include "CxxUtils/stall.h"
#include <atomic>
 
 
namespace CxxUtils {
 
 
template <class T>
inline
T atomic_bounded_decrement (std::atomic<T>* a, T bound = 0, T decr = 1,
                            std::memory_order memorder = std::memory_order_seq_cst)
{
  T orig = a->load (memorder);
  // Be careful with the comparison here --- it needs to work for
  // unsigned values, so we don't want to subtract decr from orig.
  while (orig >= bound + decr &&
         !a->compare_exchange_strong (orig, orig - decr, memorder)) {
    CxxUtils::stall();
  }
  return orig;
}
 
 
} // namespace CxxUtils
 
 
#endif // not CXXUTILS_ATOMIC_BOUNDED_DECREMENT_H