bst_lock_manber.c

/******************************************************************************
 * bst_lock_manber.c
 *
 * Lock-based binary search trees (BSTs), based on:
 *  Udi Manber and Richard E. Ladner.
 *  "Concurrency control in a dynamic search structure".
 *  ACM Transactions on Database Systems, Vol. 9, No. 3, September 1984.
 *
 * Copyright (c) 2002-2003, 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 <ucontext.h>
#include <signal.h>
#include <stdio.h>
#include <limits.h>
#include <errno.h>
#include <stdlib.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdarg.h>
#include "portable_defns.h"
#include "gc.h"
#include "set.h"

#define GARBAGE_FLAG   1
#define REDUNDANT_FLAG 2

#define IS_GARBAGE(_n)   ((int)(_n)->v & GARBAGE_FLAG)
#define MK_GARBAGE(_n)   \
    ((_n)->v = (setval_t)((unsigned long)(_n)->v | GARBAGE_FLAG))

#define IS_REDUNDANT(_n) ((int)(_n)->v & REDUNDANT_FLAG)
#define MK_REDUNDANT(_n) \
    ((_n)->v = (setval_t)((unsigned long)(_n)->v | REDUNDANT_FLAG))

#define GET_VALUE(_n) ((setval_t)((unsigned long)(_n)->v & ~3UL))

#define FOLLOW(_n, _k) (((_n)->k < (_k)) ? (_n)->r : (_n)->l)

typedef struct node_st node_t;
typedef struct set_st set_t;

struct node_st
{
    setkey_t k;
    setval_t v;
    node_t *l, *r, *p;
    int copy;
    mcs_lock_t lock;
};

struct set_st
{
    node_t root;
};

static int gc_id, hook_id;

#define LOCK(_n, _pqn)   mcs_lock(&(_n)->lock, (_pqn))
#define UNLOCK(_n, _pqn) mcs_unlock(&(_n)->lock, (_pqn))


static node_t *weak_search(node_t *n, setkey_t k)
{
    while ( (n != NULL) && (n->k != k) ) n = FOLLOW(n, k);
    return n;
}


static node_t *strong_search(node_t *n, setkey_t k, qnode_t *qn)
{
    node_t *b = n;
    node_t *a = FOLLOW(b, k);

 retry:
    while ( (a != NULL) && (a->k != k) )
    {
        b = a;
        a = FOLLOW(a, k);
    }

    if ( a == NULL )
    {
        LOCK(b, qn);
        if ( IS_GARBAGE(b) )
        {
            UNLOCK(b, qn);
            a = b->p;
            goto retry;
        }
        else if ( (a = FOLLOW(b, k)) != NULL )
        {
            UNLOCK(b, qn);
            goto retry;
        }

        a = b;
    }
    else
    {
        LOCK(a, qn);
        if ( IS_GARBAGE(a) )
        {
            UNLOCK(a, qn);
            a = a->p;
            goto retry;
        }
        else if ( IS_REDUNDANT(a) )
        {
            UNLOCK(a, qn);
            a = a->r;
            goto retry;
        }
    }

    return a;
}


static void redundancy_removal(ptst_t *ptst, void *x)
{
    node_t *d, *e, *r;
    qnode_t d_qn, e_qn;
    setkey_t k;

    if ( x == NULL ) return;

    e = x;
    k = e->k;

    if ( e->copy )
    {
        r = weak_search(e->l, k);
        assert((r == NULL) || !IS_REDUNDANT(r) || (r->r == e));
        assert(r != e);
        redundancy_removal(ptst, r);
    }

    do {
        if ( IS_GARBAGE(e) ) return;
        d = e->p;
        LOCK(d, &d_qn);
        if ( IS_GARBAGE(d) ) UNLOCK(d, &d_qn);
    }
    while ( IS_GARBAGE(d) );

    LOCK(e, &e_qn);

    if ( IS_GARBAGE(e) || !IS_REDUNDANT(e) ) goto out_de;

    if ( d->l == e )
    {
        d->l = e->l;
    }
    else
    {
        assert(d->r == e);
        d->r = e->l;
    }

    assert(e->r != NULL);
    assert(e->r->k == k);
    assert(e->r->copy);
    assert(!IS_GARBAGE(e->r));
    assert(!e->copy);

    MK_GARBAGE(e);

    if ( e->l != NULL ) e->l->p = d;

    e->r->copy = 0;

    gc_free(ptst, e, gc_id);

 out_de:
    UNLOCK(d, &d_qn);
    UNLOCK(e, &e_qn);
}


/* NB. Node X is not locked on entry. */
static void predecessor_substitution(ptst_t *ptst, set_t *s, node_t *x)
{
    node_t *a, *b, *e, *f, **pac;
    qnode_t a_qn, b_qn, e_qn, f_qn;
    setkey_t k;

    b = x;
    k = x->k;

    do {
        if ( (b == NULL) || (b->v != NULL) ) return;
        a = b->p;
        LOCK(a, &a_qn);
        if ( IS_GARBAGE(a) ) UNLOCK(a, &a_qn);
    }
    while ( IS_GARBAGE(a) );

 regain_lock:
    LOCK(b, &b_qn);

    /*
     * We do nothing if:
     *  1. The node is already deleted (and is thus garbage); or
     *  2. The node is redundant (redundancy removal will do it); or
     *  3. The node has been reused.
     * These can all be checked by looking at the value field.
     */
    if ( b->v != NULL ) goto out_ab;

    /*
     * If this node is a copy, then we can do redundancy removal right now.
     * This is an improvement over Manber and Ladner's work.
     */
    if ( b->copy )
    {
        e = weak_search(b->l, k);
        UNLOCK(b, &b_qn);
        assert((e == NULL) || !IS_REDUNDANT(e) || (e->r == b));
        assert(e != b);
        redundancy_removal(ptst, e);
        goto regain_lock;
    }

    pac = (a->k < k) ? &a->r : &a->l;
    assert(*pac == b);
    assert(b->p == a);

    if ( (b->l == NULL) || (b->r == NULL) )
    {
        if ( b->r == NULL ) *pac = b->l; else *pac = b->r;
        MK_GARBAGE(b);
        if ( *pac != NULL ) (*pac)->p = a;
        gc_free(ptst, b, gc_id);
        goto out_ab;
    }
    else
    {
        e = strong_search(b->l, b->k, &e_qn);
        assert(!IS_REDUNDANT(e) && !IS_GARBAGE(e) && (b != e));
        assert(e->k < b->k);
        f = gc_alloc(ptst, gc_id);
        f->k = e->k;
        f->v = GET_VALUE(e);
        f->copy = 1;
        f->r = b->r;
        f->l = b->l;
        mcs_init(&f->lock);
        LOCK(f, &f_qn);

        e->r = f;
        MK_REDUNDANT(e);
        *pac = f;
        f->p = a;
        f->r->p = f;
        f->l->p = f;

        MK_GARBAGE(b);
        gc_free(ptst, b, gc_id);
        gc_add_ptr_to_hook_list(ptst, e, hook_id);
        UNLOCK(e, &e_qn);
        UNLOCK(f, &f_qn);
    }

 out_ab:
    UNLOCK(a, &a_qn);
    UNLOCK(b, &b_qn);
}


set_t *set_alloc(void)
{
    set_t *s;

    s = malloc(sizeof(*s));
    mcs_init(&s->root.lock);
    s->root.k = SENTINEL_KEYMIN;
    /* Dummy root isn't redundant, nor is it garbage. */
    s->root.v = (setval_t)(~3UL);
    s->root.l = NULL;
    s->root.r = NULL;
    s->root.p = NULL;
    s->root.copy = 0;

    return s;
}


setval_t set_update(set_t *s, setkey_t k, setval_t v, int overwrite)
{
    node_t  *a, *new;
    qnode_t  qn;
    setval_t ov = NULL;
    ptst_t  *ptst;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    a = strong_search(&s->root, k, &qn);
    if ( a->k != k )
    {
        new = gc_alloc(ptst, gc_id);
        mcs_init(&new->lock);
        new->k = k;
        new->v = v;
        new->l = NULL;
        new->r = NULL;
        new->p = a;
        new->copy = 0;
        if ( a->k < k ) a->r = new; else a->l = new;
    }
    else
    {
        /* Direct A->V access is okay, as A isn't garbage or redundant. */
        ov = a->v;
        if ( overwrite || (ov == NULL) ) a->v = v;
    }

    UNLOCK(a, &qn);

    critical_exit(ptst);

    return ov;
}


setval_t set_remove(set_t *s, setkey_t k)
{
    node_t *a;
    qnode_t qn;
    setval_t v = NULL;
    ptst_t *ptst;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    a = strong_search(&s->root, k, &qn);
    /* Direct check of A->V is okay, as A isn't garbage or redundant. */
    if ( (a->k == k) && (a->v != NULL) )
    {
        v = a->v;
        a->v = NULL;
        UNLOCK(a, &qn);
        predecessor_substitution(ptst, s, a);
    }
    else
    {
        UNLOCK(a, &qn);
    }

    critical_exit(ptst);

    return v;
}


setval_t set_lookup(set_t *s, setkey_t k)
{
    node_t *n;
    setval_t v = NULL;
    ptst_t *ptst;

    k = CALLER_TO_INTERNAL_KEY(k);

    ptst = critical_enter();

    n = weak_search(&s->root, k);
    if ( n != NULL ) v = GET_VALUE(n);

    critical_exit(ptst);
    return v;
}


void _init_set_subsystem(void)
{
    gc_id = gc_add_allocator(sizeof(node_t));
    hook_id = gc_add_hook(redundancy_removal);
}