sstmutex.h

// Copyright 2009-2020 NTESS. Under the terms
// of Contract DE-NA0003525 with NTESS, the U.S.
// Government retains certain rights in this software.
//
// Copyright (c) 2009-2020, 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 _H_SST_CORE_INTERPROCESS_MUTEX
#define _H_SST_CORE_INTERPROCESS_MUTEX

#include <sched.h>
#include <time.h>

namespace SST {
namespace Core {
namespace 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");
#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;

};

}
}
}

#endif