power_play/src/base/base_futex.c

SharedFutexState shared_futex_state = ZI;

////////////////////////////////
//~ Startup

void InitFutexSystem(void)
{
    SharedFutexState *g = &shared_futex_state;
}

////////////////////////////////
//~ State helpers

FiberNeqFutexState *FiberNeqFutexStateFromId(i16 fiber_id)
{
    return &shared_futex_state.fiber_neq_states[fiber_id];
}

////////////////////////////////
//~ Not-equal futex operations

void FutexYieldNeq(volatile void *addr, void *cmp, u8 cmp_size)
{
    SharedFutexState *g = &shared_futex_state;
    FutexNeqListBin *bin = &g->neq_bins[RandU64FromSeed((u64)addr) % countof(g->neq_bins)];

    b32 cancel = 0;

    LockTicketMutex(&bin->tm);
    {
        /* Now that bin is locked, check if we should cancel insertion based on current value at address */
        {
            union
            {
                volatile void *v;
                Atomic8  *v8;
                Atomic16 *v16;
                Atomic32 *v32;
                Atomic64 *v64;
            } addr_atomic;
            union
            {
                void *v;
                i8 *v8;
                i16 *v16;
                i32 *v32;
                i64 *v64;
            } cmp_int;
            addr_atomic.v = addr;
            cmp_int.v = cmp;
            switch(cmp_size)
            {
                default: Assert(0); cancel = 1; break;  /* Invalid futex size */
                case 1: cancel = Atomic8Fetch(addr_atomic.v8)   != *cmp_int.v8; break;
                case 2: cancel = Atomic16Fetch(addr_atomic.v16) != *cmp_int.v16; break;
                case 4: cancel = Atomic32Fetch(addr_atomic.v32) != *cmp_int.v32; break;
                case 8: cancel = Atomic64Fetch(addr_atomic.v64) != *cmp_int.v64; break;
            }
        }
        if (!cancel)
        {
            /* Grab futex list from address */
            FutexNeqList *list = 0;
            {
                list = bin->first;
                for (; list; list = list->next)
                {
                    if (list->addr == addr) break;
                }
                if (!list)
                {
                    if (bin->first_free)
                    {
                        list = bin->first_free;
                        bin->first_free = list->next;
                        ZeroStruct(list);
                    }
                    else
                    {
                        Arena *perm = PermArena();
                        PushAlign(perm, CachelineSize);
                        list = PushStruct(perm, FutexNeqList);
                        PushAlign(perm, CachelineSize);
                        list->addr = addr;
                    }
                    list->next = bin->first;
                    bin->first = list;
                }
            }

            /* Insert */
            {
                i16 fiber_id = FiberId();
                FiberNeqFutexState *f = FiberNeqFutexStateFromId(fiber_id);
                f->next = list->first;
                list->first = fiber_id;
            }
        }
    }
    UnlockTicketMutex(&bin->tm);

    /* Suspend */
    if (!cancel)
    {
        SuspendFiber();
    }
}

void FutexWakeNeq(void *addr)
{
    SharedFutexState *g = &shared_futex_state;
    FutexNeqListBin *bin = &g->neq_bins[RandU64FromSeed((u64)addr) % countof(g->neq_bins)];

    /* Pull waiting ids */
    i16 first_id = 0;
    {
        LockTicketMutex(&bin->tm);
        {
            FutexNeqList *list = bin->first;
            for (; list; list = list->next)
            {
                if (list->addr == addr) break;
            }
            if (list)
            {
                first_id = list->first;
                /* Free futex list */
                {
                    FutexNeqList *prev = list->prev;
                    FutexNeqList *next = list->next;
                    if (prev)
                    {
                        prev->next = next;
                    }
                    else
                    {
                        bin->first = next;
                    }
                    if (next)
                    {
                        next->prev = prev;
                    }
                    list->next = bin->first_free;
                    bin->first_free = list;
                }
            }
        }
        UnlockTicketMutex(&bin->tm);
    }

    /* Resume fibers */
    if (first_id != 0)
    {
        TempArena scratch = BeginScratchNoConflict();
        i16 *ids = PushDry(scratch.arena, i16);
        i16 ids_count = 0;
        {
            i16 id = first_id;
            while (id != 0)
            {
                FiberNeqFutexState *f = FiberNeqFutexStateFromId(id);
                *PushStructNoZero(scratch.arena, i16) = id;
                ++ids_count;
                id = FiberNeqFutexStateFromId(id)->next;
            }
        }
        ResumeFibers(ids_count, ids);
        EndScratch(scratch);
    }
}

////////////////////////////////
//~ Greater-than-or-equal futex operations

void FutexYieldGte(volatile void *addr, void *cmp, u8 cmp_size)
{
    /* TODO: Actually implement this. Just emulating via neq for now. */
    FutexYieldNeq(addr, cmp, cmp_size);
}

void FutexWakeGte(void *addr)
{
    /* TODO: Actually implement this. Just emulating via neq for now. */
    FutexWakeNeq(addr);
}