atomic_fetch_minmax.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
/*
 * Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration.
 */
 
 
#ifndef CXXUTILS_ATOMIC_FETCH_MINMAX_H
#define CXXUTILS_ATOMIC_FETCH_MINMAX_H
 
 
#include "CxxUtils/stall.h"
#include <atomic>
 
 
namespace CxxUtils {
 
 
#if __cpp_lib_atomic_min_max
 
 
// As of C++26, these are available in stdlib.
 
 
using std::atomic_fetch_min;
using std::atomic_fetch_max;
 
 
#else
 

template <class T>
inline
T atomic_fetch_max (std::atomic<T>* a, T v,
                    std::memory_order memorder = std::memory_order_seq_cst)
{
  T orig = a->load (memorder);
  while (v > orig && !a->compare_exchange_strong (orig, v, memorder)) {
    CxxUtils::stall();
  }
  return orig;
}
 

template <class T>
inline
T atomic_fetch_min (std::atomic<T>* a, T v,
                    std::memory_order memorder = std::memory_order_seq_cst)
{
  T orig = a->load (memorder);
  while (v < orig && !a->compare_exchange_strong (orig, v, memorder)) {
    CxxUtils::stall();
  }
  return orig;
}
 
 
#endif
 
 
} // namespace CxxUtils
 
 
#endif // not CXXUTILS_ATOMIC_FETCH_MINMAX_H