sstmutex.h

// Copyright 2009-2019 NTESS. Under the terms
// of Contract DE-NA0003525 with NTESS, the U.S.
// Government retains certain rights in this software.
//
// Copyright (c) 2009-2019, 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