spin_delay.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2020, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2020, Knut Reinert & MPI für molekulare Genetik
// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
// -----------------------------------------------------------------------------------------------------
 
#pragma once
 
#include <thread>
 
#if defined(__SSE2__)  // AMD and Intel
#include <xmmintrin.h>  // _mm_pause()
#endif
 
#include <seqan3/core/platform.hpp>
 
namespace seqan3::detail
{
class spin_delay
{
public:
    constexpr spin_delay()                               noexcept = default;  
    constexpr spin_delay(spin_delay const &)             noexcept = default;  
    constexpr spin_delay(spin_delay &&)                  noexcept = default;  
    constexpr spin_delay & operator=(spin_delay const &) noexcept = default;  
    constexpr spin_delay & operator=(spin_delay &&)      noexcept = default;  
    ~spin_delay()                                        noexcept = default;  
 
    void wait()
    {
        if (current <= max_repetitions)  // Start active spinning phase
        {
            for (int_fast32_t i = 0; i < current; ++i)
                pause_processor();
            current <<= 1;  // double the amount of active CPU waiting cycles.
        }
        else  // Start passive spinning phase
        {
            std::this_thread::yield();
        }
    }
 
private:
 
    void pause_processor()
    {
        #if defined(__SSE2__)  // AMD and Intel
            _mm_pause();
        #elif defined(__armel__) || defined(__ARMEL__) // arm, but broken? ; repeat of default case as armel also defines __arm__
            asm volatile ("nop" ::: "memory");  // default operation - does nothing => Might lead to passive spinning.
        #elif defined(__arm__) || defined(__aarch64__) // arm big endian / arm64
            __asm__ __volatile__ ("yield" ::: "memory");
        #elif defined(__ia64__)  // IA64
            __asm__ __volatile__ ("hint @pause");
        #elif defined(__powerpc__) || defined(__ppc__) || defined(__PPC__) // PowerPC
            __asm__ __volatile__ ("or 27,27,27" ::: "memory");
        #else  // everything else.
            asm volatile ("nop" ::: "memory");  // default operation - does nothing => Might lead to passive spinning.
        #endif
    }
 
    static constexpr int_fast32_t max_repetitions{16};
    int_fast32_t                  current{1};
};
 
} // namespace seqan3::detail