power_play/src/platform/platform_snc.c

////////////////////////////////
//~ Mutex

//- Exclusive mutex lock
P_Lock P_LockSpinE(P_Mutex *m, i32 spin)
{
    b32 locked = 0;
    i32 spin_cnt = 0;
    while (!locked)
    {
        ++spin_cnt;
        u32 v = Atomic32FetchTestSet(&m->v, 0, 0x80000000);
        if (v == 0)
        {
            locked = 1;
        }
        else if (v == 0x40000000)
        {
            /* Lock has pending bit set, try to lock */
            u32 swp = Atomic32FetchTestSet(&m->v, v, 0x80000000);
            while (swp != v && swp == 0x40000000)
            {
                v = swp;
                swp = Atomic32FetchTestSet(&m->v, v, 0x80000000);
            }
            v = swp;
            if (v == 0x40000000)
            {
                locked = 1;
            }
        }
        if (!locked && (v & 0xC0000000) == 0)
        {
            /* Lock has shared lockers and no pending waiter, set pending bit */
            u32 swp = Atomic32FetchTestSet(&m->v, v, v | 0x40000000);
            while (swp != v && (swp & 0xC0000000) == 0 && swp != 0)
            {
                v = swp;
                swp = Atomic32FetchTestSet(&m->v, v, v | 0x40000000);
            }
            v = swp;
        }
        /* Pause or wait */
        if (!locked && v != 0 && v != 0x40000000)
        {
            if (spin_cnt < spin)
            {
                IxPause();
            }
            else
            {
                P_Wait(&m->v, &v, 4, I64Max);
                spin_cnt = 0;
            }
        }
    }

#if RtcIsEnabled
    Atomic32FetchSet(&m->exclusive_fiber_id, FiberId());
#endif

    P_Lock lock = ZI;
    lock.exclusive = 1;
    lock.mutex = m;
    return lock;
}

//- Shared mutex lock
P_Lock P_LockSpinS(P_Mutex *m, i32 spin)
{
    b32 locked = 0;
    i32 spin_cnt = 0;
    while (!locked)
    {
        ++spin_cnt;
        u32 v = Atomic32Fetch(&m->v);
        while (!locked && (v & 0xC0000000) == 0)
        {
            /* Lock has no exclusive or pending exclusive lock, increment shared count */
            u32 swp = Atomic32FetchTestSet(&m->v, v, v + 1);
            if (v == swp)
            {
                locked = 1;
            }
            else
            {
                v = swp;
            }
        }
        /* Pause or wait */
        if (!locked)
        {
            if (spin_cnt < spin)
            {
                IxPause();
            }
            else
            {
                P_Wait(&m->v, &v, 4, I64Max);
                spin_cnt = 0;
            }
        }
    }
    P_Lock lock = ZI;
    lock.mutex = m;
    return lock;
}

//- Mutex lock wrappers
P_Lock P_LockE(P_Mutex *m)
{
    return P_LockSpinE(m, P_DefaultMutexSpin);
}

P_Lock P_LockS(P_Mutex *m)
{
    return P_LockSpinS(m, P_DefaultMutexSpin);
}

void P_Unlock(P_Lock *l)
{
    P_Mutex *m = l->mutex;
    if (l->exclusive)
    {
#if RtcIsEnabled
        Atomic32FetchSet(&m->exclusive_fiber_id, 0);
#endif
        Atomic32FetchSet(&m->v, 0);
    }
    else
    {
        Atomic32FetchAdd(&m->v, -1);
    }
    P_Wake(&m->v, I32Max);
    ZeroStruct(l);
}

////////////////////////////////
//~ Condition variable

void P_WaitOnCv(P_Cv *cv, P_Lock *l)
{
    P_WaitOnCvTime(cv, l, I64Max);
}

void P_WaitOnCvTime(P_Cv *cv, P_Lock *l, i64 timeout_ns)
{
    u64 old_wake_gen = Atomic64Fetch(&cv->wake_gen);
    P_Mutex *mutex = l->mutex;
    b32 exclusive = l->exclusive;
    {
        P_Unlock(l);
        {
            P_Wait(&cv->wake_gen, &old_wake_gen, sizeof(old_wake_gen), timeout_ns);
        }
        if (exclusive)
        {
            *l = P_LockE(mutex);
        }
        else
        {
            *l = P_LockS(mutex);
        }
    }
}

void P_SignalCv(P_Cv *cv, i32 count)
{
    Atomic64FetchAdd(&cv->wake_gen, 1);
    P_Wake(&cv->wake_gen, count);
}

////////////////////////////////
//~ Counter

void P_CounterAdd(P_Counter *counter, i64 x)
{
    i64 old_v = Atomic64FetchAdd(&counter->v, x);
    i64 new_v = old_v + x;
    if (old_v > 0 && new_v <= 0)
    {
        P_Wake(&counter->v, I32Max);
    }
}

void P_WaitOnCounter(P_Counter *counter)
{
    i64 v = Atomic64Fetch(&counter->v);
    while (v > 0)
    {
        P_Wait(&counter->v, &v, sizeof(v), I64Max);
        v = Atomic64Fetch(&counter->v);
    }
}