sstmutex.h

// Copyright 2009-2025 NTESS. Under the terms
// of Contract DE-NA0003525 with NTESS, the U.S.
// Government retains certain rights in this software.
//
// Copyright (c) 2009-2025, NTESS
// All rights reserved.
//
// This file is part of the SST software package. For license
// information, see the LICENSE file in the top level directory of the
// distribution.
 
#ifndef SST_CORE_INTERPROCESS_MUTEX_H
#define SST_CORE_INTERPROCESS_MUTEX_H
 
#include <sched.h>
#include <time.h>
 
namespace SST::Core::Interprocess {
 
#define SST_CORE_INTERPROCESS_LOCKED   1
#define SST_CORE_INTERPROCESS_UNLOCKED 0
 
class SSTMutex
{
 
public:
    SSTMutex() { lockVal = SST_CORE_INTERPROCESS_UNLOCKED; }
 
    void processorPause(int currentCount)
    {
        if ( currentCount < 64 ) {
#if defined(__x86_64__)
            __asm__ __volatile__("pause" : : : "memory");
#elif (defined(__arm__) || defined(__aarch64__))
            __asm__ __volatile__("yield");
#else
            // Put some pause code in here
#endif
        }
        else if ( currentCount < 256 ) {
            sched_yield();
        }
        else {
            struct timespec sleepPeriod;
            sleepPeriod.tv_sec  = 0;
            sleepPeriod.tv_nsec = 100;
 
            struct timespec interPeriod;
            nanosleep(&sleepPeriod, &interPeriod);
        }
    }
 
    void lock()
    {
        int loop_counter = 0;
 
        while (
            !__sync_bool_compare_and_swap(&lockVal, SST_CORE_INTERPROCESS_UNLOCKED, SST_CORE_INTERPROCESS_LOCKED) ) {
            processorPause(loop_counter);
            loop_counter++;
        }
    }
 
    void unlock()
    {
        lockVal = SST_CORE_INTERPROCESS_UNLOCKED;
        __sync_synchronize();
    }
 
    bool try_lock()
    {
        return __sync_bool_compare_and_swap(&lockVal, SST_CORE_INTERPROCESS_UNLOCKED, SST_CORE_INTERPROCESS_LOCKED);
    }
 
private:
    volatile int lockVal;
};
 
} // namespace SST::Core::Interprocess
 
#endif // SST_CORE_INTERPROCESS_MUTEX_H