skip_stm.c

/******************************************************************************
 * skip_stm.c
 *
 * Skip lists, allowing concurrent update by use of the STM abstraction.
 *
 * Copyright (c) 2003, K A Fraser
 *

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

    * Redistributions of source code must retain the above copyright
    * notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above
    * copyright notice, this list of conditions and the following
    * disclaimer in the documentation and/or other materials provided
    * with the distribution.  Neither the name of the Keir Fraser
    * nor the names of its contributors may be used to endorse or
    * promote products derived from this software without specific
    * prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#define __SET_IMPLEMENTATION__

#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "portable_defns.h"
#include "gc.h"
#include "stm.h"
#include "set.h"

typedef struct node_st node_t;
typedef stm_blk set_t;

struct node_st
{
    int       level;
    setkey_t  k;
    setval_t  v;
    stm_blk  *next[NUM_LEVELS];
};

static struct {
    CACHE_PAD(0);
    stm *memory;    /* read-only */
    CACHE_PAD(2);
} shared;

#define MEMORY (shared.memory)

/*
 * Random level generator. Drop-off rate is 0.5 per level.
 * Returns value 1 <= level <= NUM_LEVELS.
 */
static int get_level(ptst_t *ptst)
{
    unsigned long r = rand_next(ptst);
    int l = 1;
    r = (r >> 4) & ((1 << (NUM_LEVELS-1)) - 1);
    while ( (r & 1) ) { l++; r >>= 1; }
    return l;
}


/*
 * Search for first non-deleted node, N, with key >= @k at each level in @l.
 * RETURN VALUES:
 *  Array @pa: @pa[i] is non-deleted predecessor of N at level i
 *  Array @na: @na[i] is N itself, which should be pointed at by @pa[i]
 *  MAIN RETURN VALUE: same as @na[0], direct pointer open for reading.
 */
static node_t *search_predecessors(
    ptst_t *ptst, stm_tx *tx, set_t *l, setkey_t k, stm_blk **pa, stm_blk **na)
{
    stm_blk *xb, *x_nextb;
    node_t  *x,  *x_next;
    int      i;

    xb = l;
    x  = read_stm_blk(ptst, tx, l);
    for ( i = NUM_LEVELS - 1; i >= 0; i-- )
    {
        for ( ; ; )
        {
            x_nextb = x->next[i];
            x_next  = read_stm_blk(ptst, tx, x_nextb);
            if ( x_next->k >= k ) break;
            xb = x_nextb;
            x  = x_next;
        }

        if ( pa ) pa[i] = xb;
        if ( na ) na[i] = x_nextb;
    }

    return x_next;
}


/*
 * PUBLIC FUNCTIONS
 */

set_t *set_alloc(void)
{
    ptst_t  *ptst;
    stm_blk *hb, *tb;
    node_t  *h, *t;
    int      i;

    ptst = critical_enter();

    tb = new_stm_blk(ptst, MEMORY);
    t  = init_stm_blk(ptst, MEMORY, tb);
    memset(t, 0, sizeof(*t));
    t->k = SENTINEL_KEYMAX;

    hb = new_stm_blk(ptst, MEMORY);
    h  = init_stm_blk(ptst, MEMORY, hb);
    memset(h, 0, sizeof(*h));
    h->k     = SENTINEL_KEYMIN;
    h->level = NUM_LEVELS;
    for ( i = 0; i < NUM_LEVELS; i++ )
        h->next[i] = tb;

    critical_exit(ptst);

    return hb;
}


setval_t set_update(set_t *l, setkey_t k, setval_t v, int overwrite)
{
    ptst_t   *ptst;
    stm_tx   *tx;
    setval_t  ov;
    stm_blk  *bpreds[NUM_LEVELS], *bsuccs[NUM_LEVELS], *newb = NULL;
    node_t   *x, *p, *new;
    int       i;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    do {
        new_stm_tx(tx, ptst, MEMORY);
        x = search_predecessors(ptst, tx, l, k, bpreds, bsuccs);

        if ( x->k == k )
        {
            x    = write_stm_blk(ptst, tx, bsuccs[0]);
            ov   = x->v;
            x->v = v;
        }
        else
        {
            ov = NULL;

            if ( newb == NULL )
            {
                newb = new_stm_blk(ptst, MEMORY);
                new  = init_stm_blk(ptst, MEMORY, newb);
                new->k = k;
                new->v = v;
                new->level = get_level(ptst);
            }

            for ( i = 0; i < new->level; i++ )
            {
                new->next[i] = bsuccs[i];
                p = write_stm_blk(ptst, tx, bpreds[i]);
                p->next[i] = newb;
            }
        }
    }
    while ( !commit_stm_tx(ptst, tx) );

    if ( (ov != NULL) && (newb != NULL) )
        free_stm_blk(ptst, MEMORY, newb);

    critical_exit(ptst);

    return ov;
}


setval_t set_remove(set_t *l, setkey_t k)
{
    setval_t  v;
    ptst_t   *ptst;
    stm_tx   *tx;
    stm_blk  *bpreds[NUM_LEVELS], *bsuccs[NUM_LEVELS];
    node_t   *p, *x;
    int       i;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    do {
        new_stm_tx(tx, ptst, MEMORY);
        x = search_predecessors(ptst, tx, l, k, bpreds, bsuccs);
        if ( x->k == k )
        {
            v = x->v;
            for ( i = 0; i < x->level; i++ )
            {
                p = write_stm_blk(ptst, tx, bpreds[i]);
                p->next[i] = x->next[i];
            }
        }
        else
        {
            v = NULL;
        }
    }
    while ( !commit_stm_tx(ptst, tx) );

    if ( v != NULL )
        free_stm_blk(ptst, MEMORY, bsuccs[0]);

    critical_exit(ptst);

    return v;
}


setval_t set_lookup(set_t *l, setkey_t k)
{
    setval_t  v;
    ptst_t   *ptst;
    stm_tx   *tx;
    node_t   *x;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    do {
        new_stm_tx(tx, ptst, MEMORY);
        x = search_predecessors(ptst, tx, l, k, NULL, NULL);
        v = (x->k == k) ? x->v : NULL;
    }
    while ( !commit_stm_tx(ptst, tx) );

    critical_exit(ptst);

    return v;
}


void _init_set_subsystem(void)
{
    ptst_t *ptst = critical_enter();
    _init_stm_subsystem(0);
    MEMORY = new_stm(ptst, sizeof(node_t));
    critical_exit(ptst);
}