rcuja: add fallback nodes

[userspace-rcu.git] / rcuja / rcuja.c

/*
 * rcuja/rcuja.c
 *
 * Userspace RCU library - RCU Judy Array
 *
 * Copyright 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#define _LGPL_SOURCE
#include <stdint.h>
#include <errno.h>
#include <limits.h>
#include <urcu/rcuja.h>
#include <urcu/compiler.h>
#include <urcu/arch.h>
#include <assert.h>
#include <urcu-pointer.h>
#include <urcu/uatomic.h>
#include <stdint.h>

#include "rcuja-internal.h"
#include "bitfield.h"

enum cds_ja_type_class {
        RCU_JA_LINEAR = 0,      /* Type A */
                        /* 32-bit: 1 to 25 children, 8 to 128 bytes */
                        /* 64-bit: 1 to 28 children, 16 to 256 bytes */
        RCU_JA_POOL = 1,        /* Type B */
                        /* 32-bit: 26 to 100 children, 256 to 512 bytes */
                        /* 64-bit: 29 to 112 children, 512 to 1024 bytes */
        RCU_JA_PIGEON = 2,      /* Type C */
                        /* 32-bit: 101 to 256 children, 1024 bytes */
                        /* 64-bit: 113 to 256 children, 2048 bytes */
        /* Leaf nodes are implicit from their height in the tree */
        RCU_JA_NR_TYPES,

        RCU_JA_NULL,    /* not an encoded type, but keeps code regular */
};

struct cds_ja_type {
        enum cds_ja_type_class type_class;
        uint16_t min_child;             /* minimum number of children: 1 to 256 */
        uint16_t max_child;             /* maximum number of children: 1 to 256 */
        uint16_t max_linear_child;      /* per-pool max nr. children: 1 to 256 */
        uint16_t order;                 /* node size is (1 << order), in bytes */
        uint16_t nr_pool_order;         /* number of pools */
        uint16_t pool_size_order;       /* pool size */
};

/*
 * Number of least significant pointer bits reserved to represent the
 * child type.
 */
#define JA_TYPE_BITS    3
#define JA_TYPE_MAX_NR  (1UL << JA_TYPE_BITS)
#define JA_TYPE_MASK    (JA_TYPE_MAX_NR - 1)
#define JA_PTR_MASK     (~JA_TYPE_MASK)

#define JA_ENTRY_PER_NODE       256UL
#define JA_BITS_PER_BYTE        3

#define JA_MAX_DEPTH    5       /* Maximum depth, including leafs */

/*
 * Entry for NULL node is at index 8 of the table. It is never encoded
 * in flags.
 */
#define NODE_INDEX_NULL         8

/*
 * Number of removals needed on a fallback node before we try to shrink
 * it.
 */
#define JA_FALLBACK_REMOVAL_COUNT       8

/*
 * Iteration on the array to find the right node size for the number of
 * children stops when it reaches .max_child == 256 (this is the largest
 * possible node size, which contains 256 children).
 * The min_child overlaps with the previous max_child to provide an
 * hysteresis loop to reallocation for patterns of cyclic add/removal
 * within the same node.
 * The node the index within the following arrays is represented on 3
 * bits. It identifies the node type, min/max number of children, and
 * the size order.
 * The max_child values for the RCU_JA_POOL below result from
 * statistical approximation: over million populations, the max_child
 * covers between 97% and 99% of the populations generated. Therefore, a
 * fallback should exist to cover the rare extreme population unbalance
 * cases, but it will not have a major impact on speed nor space
 * consumption, since those are rare cases.
 */

#if (CAA_BITS_PER_LONG < 64)
/* 32-bit pointers */
enum {
        ja_type_0_max_child = 1,
        ja_type_1_max_child = 3,
        ja_type_2_max_child = 6,
        ja_type_3_max_child = 12,
        ja_type_4_max_child = 25,
        ja_type_5_max_child = 48,
        ja_type_6_max_child = 92,
        ja_type_7_max_child = 256,
        ja_type_8_max_child = 0,        /* NULL */
};

enum {
        ja_type_0_max_linear_child = 1,
        ja_type_1_max_linear_child = 3,
        ja_type_2_max_linear_child = 6,
        ja_type_3_max_linear_child = 12,
        ja_type_4_max_linear_child = 25,
        ja_type_5_max_linear_child = 24,
        ja_type_6_max_linear_child = 23,
};

enum {
        ja_type_5_nr_pool_order = 1,
        ja_type_6_nr_pool_order = 2,
};

const struct cds_ja_type ja_types[] = {
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_0_max_child, .max_linear_child = ja_type_0_max_linear_child, .order = 3, },
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_1_max_child, .max_linear_child = ja_type_1_max_linear_child, .order = 4, },
        { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = ja_type_2_max_child, .max_linear_child = ja_type_2_max_linear_child, .order = 5, },
        { .type_class = RCU_JA_LINEAR, .min_child = 4, .max_child = ja_type_3_max_child, .max_linear_child = ja_type_3_max_linear_child, .order = 6, },
        { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = ja_type_4_max_child, .max_linear_child = ja_type_4_max_linear_child, .order = 7, },

        /* Pools may fill sooner than max_child */
        { .type_class = RCU_JA_POOL, .min_child = 20, .max_child = ja_type_5_max_child, .max_linear_child = ja_type_5_max_linear_child, .order = 8, .nr_pool_order = ja_type_5_nr_pool_order, .pool_size_order = 7, },
        { .type_class = RCU_JA_POOL, .min_child = 45, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 9, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 7, },

        /*
         * TODO: Upon node removal below min_child, if child pool is
         * filled beyond capacity, we need to roll back to pigeon.
         */
        { .type_class = RCU_JA_PIGEON, .min_child = 89, .max_child = ja_type_7_max_child, .order = 10, },

        { .type_class = RCU_JA_NULL, .min_child = 0, .max_child = ja_type_8_max_child, },
};
#else /* !(CAA_BITS_PER_LONG < 64) */
/* 64-bit pointers */
enum {
        ja_type_0_max_child = 1,
        ja_type_1_max_child = 3,
        ja_type_2_max_child = 7,
        ja_type_3_max_child = 14,
        ja_type_4_max_child = 28,
        ja_type_5_max_child = 54,
        ja_type_6_max_child = 104,
        ja_type_7_max_child = 256,
        ja_type_8_max_child = 256,
};

enum {
        ja_type_0_max_linear_child = 1,
        ja_type_1_max_linear_child = 3,
        ja_type_2_max_linear_child = 7,
        ja_type_3_max_linear_child = 14,
        ja_type_4_max_linear_child = 28,
        ja_type_5_max_linear_child = 27,
        ja_type_6_max_linear_child = 26,
};

enum {
        ja_type_5_nr_pool_order = 1,
        ja_type_6_nr_pool_order = 2,
};

const struct cds_ja_type ja_types[] = {
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_0_max_child, .max_linear_child = ja_type_0_max_linear_child, .order = 4, },
        { .type_class = RCU_JA_LINEAR, .min_child = 1, .max_child = ja_type_1_max_child, .max_linear_child = ja_type_1_max_linear_child, .order = 5, },
        { .type_class = RCU_JA_LINEAR, .min_child = 3, .max_child = ja_type_2_max_child, .max_linear_child = ja_type_2_max_linear_child, .order = 6, },
        { .type_class = RCU_JA_LINEAR, .min_child = 5, .max_child = ja_type_3_max_child, .max_linear_child = ja_type_3_max_linear_child, .order = 7, },
        { .type_class = RCU_JA_LINEAR, .min_child = 10, .max_child = ja_type_4_max_child, .max_linear_child = ja_type_4_max_linear_child, .order = 8, },

        /* Pools may fill sooner than max_child. */
        { .type_class = RCU_JA_POOL, .min_child = 22, .max_child = ja_type_5_max_child, .max_linear_child = ja_type_5_max_linear_child, .order = 9, .nr_pool_order = ja_type_5_nr_pool_order, .pool_size_order = 8, },
        { .type_class = RCU_JA_POOL, .min_child = 51, .max_child = ja_type_6_max_child, .max_linear_child = ja_type_6_max_linear_child, .order = 10, .nr_pool_order = ja_type_6_nr_pool_order, .pool_size_order = 8, },

        /*
         * TODO: Upon node removal below min_child, if child pool is
         * filled beyond capacity, we need to roll back to pigeon.
         */
        { .type_class = RCU_JA_PIGEON, .min_child = 101, .max_child = ja_type_7_max_child, .order = 11, },

        { .type_class = RCU_JA_NULL, .min_child = 0, .max_child = ja_type_8_max_child, },
};
#endif /* !(BITS_PER_LONG < 64) */

static inline __attribute__((unused))
void static_array_size_check(void)
{
        CAA_BUILD_BUG_ON(CAA_ARRAY_SIZE(ja_types) < JA_TYPE_MAX_NR);
}

/*
 * The cds_ja_node contains the compressed node data needed for
 * read-side. For linear and pool node configurations, it starts with a
 * byte counting the number of children in the node.  Then, the
 * node-specific data is placed.
 * The node mutex, if any is needed, protecting concurrent updated of
 * each node is placed in a separate hash table indexed by node address.
 * For the pigeon configuration, the number of children is also kept in
 * a separate hash table, indexed by node address, because it is only
 * required for updates.
 */

#define DECLARE_LINEAR_NODE(index)                                                              \
        struct {                                                                                \
                uint8_t nr_child;                                                               \
                uint8_t child_value[ja_type_## index ##_max_linear_child];                      \
                struct cds_ja_inode_flag *child_ptr[ja_type_## index ##_max_linear_child];      \
        }

#define DECLARE_POOL_NODE(index)                                                                \
        struct {                                                                                \
                struct {                                                                        \
                        uint8_t nr_child;                                                       \
                        uint8_t child_value[ja_type_## index ##_max_linear_child];              \
                        struct cds_ja_inode_flag *child_ptr[ja_type_## index ##_max_linear_child]; \
                } linear[1U << ja_type_## index ##_nr_pool_order];                              \
        }

struct cds_ja_inode {
        union {
                /* Linear configuration */
                DECLARE_LINEAR_NODE(0) conf_0;
                DECLARE_LINEAR_NODE(1) conf_1;
                DECLARE_LINEAR_NODE(2) conf_2;
                DECLARE_LINEAR_NODE(3) conf_3;
                DECLARE_LINEAR_NODE(4) conf_4;

                /* Pool configuration */
                DECLARE_POOL_NODE(5) conf_5;
                DECLARE_POOL_NODE(6) conf_6;

                /* Pigeon configuration */
                struct {
                        struct cds_ja_inode_flag *child[ja_type_7_max_child];
                } conf_7;
                /* data aliasing nodes for computed accesses */
                uint8_t data[sizeof(struct cds_ja_inode_flag *) * ja_type_7_max_child];
        } u;
};

static
struct cds_ja_inode_flag *ja_node_flag(struct cds_ja_inode *node,
                unsigned long type)
{
        assert(type < (1UL << JA_TYPE_BITS));
        return (struct cds_ja_inode_flag *) (((unsigned long) node) | type);
}

static
struct cds_ja_inode *ja_node_ptr(struct cds_ja_inode_flag *node)
{
        return (struct cds_ja_inode *) (((unsigned long) node) & JA_PTR_MASK);
}

static
unsigned long ja_node_type(struct cds_ja_inode_flag *node)
{
        unsigned long type;

        if (ja_node_ptr(node) == NULL) {
                return NODE_INDEX_NULL;
        }
        type = (unsigned int) ((unsigned long) node & JA_TYPE_MASK);
        assert(type < (1UL << JA_TYPE_BITS));
        return type;
}

struct cds_ja_inode *alloc_cds_ja_node(const struct cds_ja_type *ja_type)
{
        return calloc(1U << ja_type->order, sizeof(char));
}

void free_cds_ja_node(struct cds_ja_inode *node)
{
        free(node);
}

#define __JA_ALIGN_MASK(v, mask)        (((v) + (mask)) & ~(mask))
#define JA_ALIGN(v, align)              __JA_ALIGN_MASK(v, (typeof(v)) (align) - 1)
#define __JA_FLOOR_MASK(v, mask)        ((v) & ~(mask))
#define JA_FLOOR(v, align)              __JA_FLOOR_MASK(v, (typeof(v)) (align) - 1)

static
uint8_t *align_ptr_size(uint8_t *ptr)
{
        return (uint8_t *) JA_ALIGN((unsigned long) ptr, sizeof(void *));
}

static
uint8_t ja_linear_node_get_nr_child(const struct cds_ja_type *type,
                struct cds_ja_inode *node)
{
        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);
        return CMM_LOAD_SHARED(node->u.data[0]);
}

/*
 * The order in which values and pointers are does does not matter: if
 * a value is missing, we return NULL. If a value is there, but its
 * associated pointers is still NULL, we return NULL too.
 */
static
struct cds_ja_inode_flag *ja_linear_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag ***child_node_flag_ptr,
                uint8_t n)
{
        uint8_t nr_child;
        uint8_t *values;
        struct cds_ja_inode_flag **pointers;
        struct cds_ja_inode_flag *ptr;
        unsigned int i;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);

        nr_child = ja_linear_node_get_nr_child(type, node);
        cmm_smp_rmb();  /* read nr_child before values and pointers */
        assert(nr_child <= type->max_linear_child);
        assert(type->type_class != RCU_JA_LINEAR || nr_child >= type->min_child);

        values = &node->u.data[1];
        for (i = 0; i < nr_child; i++) {
                if (CMM_LOAD_SHARED(values[i]) == n)
                        break;
        }
        if (i >= nr_child)
                return NULL;
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        if (caa_unlikely(child_node_flag_ptr))
                *child_node_flag_ptr = &pointers[i];
        ptr = rcu_dereference(pointers[i]);
        assert(ja_node_ptr(ptr) != NULL);
        return ptr;
}

static
void ja_linear_node_get_ith_pos(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                uint8_t i,
                uint8_t *v,
                struct cds_ja_inode_flag **iter)
{
        uint8_t *values;
        struct cds_ja_inode_flag **pointers;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);
        assert(i < ja_linear_node_get_nr_child(type, node));

        values = &node->u.data[1];
        *v = values[i];
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        *iter = pointers[i];
}

static
struct cds_ja_inode_flag *ja_pool_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag ***child_node_flag_ptr,
                uint8_t n)
{
        struct cds_ja_inode *linear;

        assert(type->type_class == RCU_JA_POOL);
        /*
         * TODO: currently, we select the pool by highest bits. We
         * should support various encodings.
         */
        linear = (struct cds_ja_inode *)
                &node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
        return ja_linear_node_get_nth(type, linear, child_node_flag_ptr, n);
}

static
struct cds_ja_inode *ja_pool_node_get_ith_pool(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                uint8_t i)
{
        assert(type->type_class == RCU_JA_POOL);
        return (struct cds_ja_inode *)
                &node->u.data[(unsigned int) i << type->pool_size_order];
}

static
struct cds_ja_inode_flag *ja_pigeon_node_get_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_inode_flag ***child_node_flag_ptr,
                uint8_t n)
{
        struct cds_ja_inode_flag **child_node_flag;

        assert(type->type_class == RCU_JA_PIGEON);
        child_node_flag = &((struct cds_ja_inode_flag **) node->u.data)[n];
        if (caa_unlikely(child_node_flag_ptr))
                *child_node_flag_ptr = child_node_flag;
        return rcu_dereference(*child_node_flag);
}

/*
 * ja_node_get_nth: get nth item from a node.
 * node_flag is already rcu_dereference'd.
 */
static
struct cds_ja_inode_flag * ja_node_get_nth(struct cds_ja_inode_flag *node_flag,
                struct cds_ja_inode_flag ***child_node_flag_ptr,
                uint8_t n)
{
        unsigned int type_index;
        struct cds_ja_inode *node;
        const struct cds_ja_type *type;

        node = ja_node_ptr(node_flag);
        assert(node != NULL);
        type_index = ja_node_type(node_flag);
        type = &ja_types[type_index];

        switch (type->type_class) {
        case RCU_JA_LINEAR:
                return ja_linear_node_get_nth(type, node,
                                child_node_flag_ptr, n);
        case RCU_JA_POOL:
                return ja_pool_node_get_nth(type, node,
                                child_node_flag_ptr, n);
        case RCU_JA_PIGEON:
                return ja_pigeon_node_get_nth(type, node,
                                child_node_flag_ptr, n);
        default:
                assert(0);
                return (void *) -1UL;
        }
}

/*
 * TODO: use ja_get_nr_child to monitor limits triggering shrink
 * recompaction.
 * Also use ja_get_nr_child to make the difference between resize and
 * pool change of compaction bit(s).
 */
static
unsigned int ja_get_nr_child(struct cds_ja_shadow_node *shadow_node)
{
        return shadow_node->nr_child;
}

static
int ja_linear_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        uint8_t nr_child;
        uint8_t *values, *nr_child_ptr;
        struct cds_ja_inode_flag **pointers;
        unsigned int i;

        assert(type->type_class == RCU_JA_LINEAR || type->type_class == RCU_JA_POOL);

        nr_child_ptr = &node->u.data[0];
        dbg_printf("linear set nth: nr_child_ptr %p\n", nr_child_ptr);
        nr_child = *nr_child_ptr;
        assert(nr_child <= type->max_linear_child);

        values = &node->u.data[1];
        for (i = 0; i < nr_child; i++) {
                if (values[i] == n)
                        return -EEXIST;
        }
        if (nr_child >= type->max_linear_child) {
                /* No space left in this node type */
                return -ENOSPC;
        }
        pointers = (struct cds_ja_inode_flag **) align_ptr_size(&values[type->max_linear_child]);
        assert(pointers[nr_child] == NULL);
        rcu_assign_pointer(pointers[nr_child], child_node_flag);
        CMM_STORE_SHARED(values[nr_child], n);
        cmm_smp_wmb();  /* write value and pointer before nr_child */
        CMM_STORE_SHARED(*nr_child_ptr, nr_child + 1);
        shadow_node->nr_child++;
        dbg_printf("linear set nth: %u child, shadow: %u child, for node %p shadow %p\n",
                (unsigned int) CMM_LOAD_SHARED(*nr_child_ptr),
                (unsigned int) shadow_node->nr_child,
                node, shadow_node);

        return 0;
}

static
int ja_pool_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        struct cds_ja_inode *linear;

        assert(type->type_class == RCU_JA_POOL);
        linear = (struct cds_ja_inode *)
                &node->u.data[((unsigned long) n >> (CHAR_BIT - type->nr_pool_order)) << type->pool_size_order];
        return ja_linear_node_set_nth(type, linear, shadow_node,
                        n, child_node_flag);
}

static
int ja_pigeon_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        struct cds_ja_inode_flag **ptr;

        assert(type->type_class == RCU_JA_PIGEON);
        ptr = &((struct cds_ja_inode_flag **) node->u.data)[n];
        if (*ptr)
                return -EEXIST;
        rcu_assign_pointer(*ptr, child_node_flag);
        shadow_node->nr_child++;
        return 0;
}

/*
 * _ja_node_set_nth: set nth item within a node. Return an error
 * (negative error value) if it is already there.
 * TODO: exclusive access on node.
 */
static
int _ja_node_set_nth(const struct cds_ja_type *type,
                struct cds_ja_inode *node,
                struct cds_ja_shadow_node *shadow_node,
                uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        switch (type->type_class) {
        case RCU_JA_LINEAR:
                return ja_linear_node_set_nth(type, node, shadow_node, n,
                                child_node_flag);
        case RCU_JA_POOL:
                return ja_pool_node_set_nth(type, node, shadow_node, n,
                                child_node_flag);
        case RCU_JA_PIGEON:
                return ja_pigeon_node_set_nth(type, node, shadow_node, n,
                                child_node_flag);
        case RCU_JA_NULL:
                return -ENOSPC;
        default:
                assert(0);
                return -EINVAL;
        }

        return 0;
}

/*
 * ja_node_recompact_add: recompact a node, adding a new child.
 * TODO: for pool type, take selection bit(s) into account.
 * Return 0 on success, -ENOENT if need to retry, or other negative
 * error value otherwise.
 */
static
int ja_node_recompact_add(struct cds_ja *ja,
                unsigned int old_type_index,
                const struct cds_ja_type *old_type,
                struct cds_ja_inode *old_node,
                struct cds_ja_shadow_node *shadow_node,
                struct cds_ja_inode_flag **old_node_flag, uint8_t n,
                struct cds_ja_inode_flag *child_node_flag)
{
        unsigned int new_type_index;
        struct cds_ja_inode *new_node;
        struct cds_ja_shadow_node *new_shadow_node;
        const struct cds_ja_type *new_type;
        struct cds_ja_inode_flag *new_node_flag;
        int ret;
        int fallback = 0;

        if (!shadow_node || old_type_index == NODE_INDEX_NULL) {
                new_type_index = 0;
        } else {
                new_type_index = old_type_index + 1;
        }

retry:          /* for fallback */
        dbg_printf("Recompact to type %d\n", new_type_index);
        new_type = &ja_types[new_type_index];
        new_node = alloc_cds_ja_node(new_type);
        if (!new_node)
                return -ENOMEM;
        new_node_flag = ja_node_flag(new_node, new_type_index);

        dbg_printf("Recompact inherit lock from %p\n", shadow_node);
        new_shadow_node = rcuja_shadow_set(ja->ht, new_node, shadow_node);
        if (!new_shadow_node) {
                free(new_node);
                return -ENOMEM;
        }
        if (fallback)
                new_shadow_node->fallback_removal_count =
                                        JA_FALLBACK_REMOVAL_COUNT;

        assert(old_type->type_class != RCU_JA_PIGEON);
        switch (old_type->type_class) {
        case RCU_JA_LINEAR:
        {
                uint8_t nr_child =
                        ja_linear_node_get_nr_child(old_type, old_node);
                unsigned int i;

                for (i = 0; i < nr_child; i++) {
                        struct cds_ja_inode_flag *iter;
                        uint8_t v;

                        ja_linear_node_get_ith_pos(old_type, old_node, i, &v, &iter);
                        if (!iter)
                                continue;
                        ret = _ja_node_set_nth(new_type, new_node,
                                        new_shadow_node,
                                        v, iter);
                        if (new_type->type_class == RCU_JA_POOL && ret) {
                                goto fallback_toosmall;
                        }
                        assert(!ret);
                }
                break;
        }
        case RCU_JA_POOL:
        {
                unsigned int pool_nr;

                for (pool_nr = 0; pool_nr < (1U << old_type->nr_pool_order); pool_nr++) {
                        struct cds_ja_inode *pool =
                                ja_pool_node_get_ith_pool(old_type,
                                        old_node, pool_nr);
                        uint8_t nr_child =
                                ja_linear_node_get_nr_child(old_type, pool);
                        unsigned int j;

                        for (j = 0; j < nr_child; j++) {
                                struct cds_ja_inode_flag *iter;
                                uint8_t v;

                                ja_linear_node_get_ith_pos(old_type, pool,
                                                j, &v, &iter);
                                if (!iter)
                                        continue;
                                ret = _ja_node_set_nth(new_type, new_node,
                                                new_shadow_node,
                                                v, iter);
                                if (new_type->type_class == RCU_JA_POOL
                                                && ret) {
                                        goto fallback_toosmall;
                                }
                                assert(!ret);
                        }
                }
                break;
        }
        case RCU_JA_NULL:
                /* Nothing to copy */
                break;
        case RCU_JA_PIGEON:
        default:
                assert(0);
                ret = -EINVAL;
                goto end;
        }

        /* add node */
        ret = _ja_node_set_nth(new_type, new_node,
                        new_shadow_node,
                        n, child_node_flag);
        assert(!ret);
        /* Return pointer to new recompacted new through old_node_flag */
        *old_node_flag = new_node_flag;
        if (old_node) {
                ret = rcuja_shadow_clear(ja->ht, old_node, shadow_node,
                                RCUJA_SHADOW_CLEAR_FREE_NODE);
                assert(!ret);
        }

        ret = 0;
end:
        return ret;

fallback_toosmall:
        /* fallback if next pool is too small */
        ret = rcuja_shadow_clear(ja->ht, new_node, new_shadow_node,
                        RCUJA_SHADOW_CLEAR_FREE_NODE);
        assert(!ret);

        /* Last type: pigeon */
        new_type_index = (1UL << JA_TYPE_BITS) - 1;
        dbg_printf("Fallback to type %d\n", new_type_index);
        uatomic_inc(&ja->nr_fallback);
        fallback = 1;
        goto retry;
}

/*
 * Return 0 on success, -ENOENT if need to retry, or other negative
 * error value otherwise.
 */
static
int ja_node_set_nth(struct cds_ja *ja,
                struct cds_ja_inode_flag **node_flag, uint8_t n,
                struct cds_ja_inode_flag *child_node_flag,
                struct cds_ja_shadow_node *shadow_node)
{
        int ret;
        unsigned int type_index;
        const struct cds_ja_type *type;
        struct cds_ja_inode *node;

        dbg_printf("ja_node_set_nth for n=%u, node %p, shadow %p\n",
                (unsigned int) n, ja_node_ptr(*node_flag), shadow_node);

        node = ja_node_ptr(*node_flag);
        type_index = ja_node_type(*node_flag);
        type = &ja_types[type_index];
        ret = _ja_node_set_nth(type, node, shadow_node,
                        n, child_node_flag);
        if (ret == -ENOSPC) {
                /* Not enough space in node, need to recompact. */
                ret = ja_node_recompact_add(ja, type_index, type, node,
                                shadow_node, node_flag, n, child_node_flag);
        }
        return ret;
}

struct cds_hlist_head *cds_ja_lookup(struct cds_ja *ja, uint64_t key)
{
        unsigned int tree_depth, i;
        struct cds_ja_inode_flag *node_flag;

        if (caa_unlikely(key > ja->key_max))
                return NULL;
        tree_depth = ja->tree_depth;
        node_flag = rcu_dereference(ja->root);

        /* level 0: root node */
        if (!ja_node_ptr(node_flag))
                return NULL;

        for (i = 1; i < tree_depth; i++) {
                node_flag = ja_node_get_nth(node_flag, NULL,
                        (unsigned char) key);
                if (!ja_node_ptr(node_flag))
                        return NULL;
                key >>= JA_BITS_PER_BYTE;
        }

        /* Last level lookup succeded. We got an actual match. */
        return (struct cds_hlist_head *) node_flag;
}

/*
 * We reached an unpopulated node. Create it and the children we need,
 * and then attach the entire branch to the current node. This may
 * trigger recompaction of the current node.  Locks needed: node lock
 * (for add), and, possibly, parent node lock (to update pointer due to
 * node recompaction).
 *
 * First take node lock, check if recompaction is needed, then take
 * parent lock (if needed).  Then we can proceed to create the new
 * branch. Publish the new branch, and release locks.
 * TODO: we currently always take the parent lock even when not needed.
 */
static
int ja_attach_node(struct cds_ja *ja,
                struct cds_ja_inode_flag **node_flag_ptr,
                struct cds_ja_inode_flag *node_flag,
                struct cds_ja_inode_flag *parent_node_flag,
                uint64_t key,
                unsigned int depth,
                struct cds_ja_node *child_node)
{
        struct cds_ja_shadow_node *shadow_node = NULL,
                        *parent_shadow_node = NULL,
                        *iter_shadow_node;
        struct cds_ja_inode *node = ja_node_ptr(node_flag);
        struct cds_ja_inode *parent_node = ja_node_ptr(parent_node_flag);
        struct cds_hlist_head head;
        struct cds_ja_inode_flag *iter_node_flag, *iter_dest_node_flag;
        int ret, i;
        struct cds_ja_inode_flag *created_nodes[JA_MAX_DEPTH];
        int nr_created_nodes = 0;

        dbg_printf("Attach node at depth %u\n", depth);

        assert(node);
        shadow_node = rcuja_shadow_lookup_lock(ja->ht, node);
        if (!shadow_node) {
                ret = -ENOENT;
                goto end;
        }
        if (parent_node) {
                parent_shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                                                parent_node);
                if (!parent_shadow_node) {
                        ret = -ENOENT;
                        goto unlock_shadow;
                }
        }

        /* Create new branch, starting from bottom */
        CDS_INIT_HLIST_HEAD(&head);
        cds_hlist_add_head_rcu(&child_node->list, &head);
        iter_node_flag = (struct cds_ja_inode_flag *) head.next;

        /* Create shadow node for the leaf node */
        dbg_printf("leaf shadow node creation\n");
        iter_shadow_node = rcuja_shadow_set(ja->ht,
                        ja_node_ptr(iter_node_flag), NULL);
        if (!iter_shadow_node) {
                ret = -ENOMEM;
                goto check_error;
        }
        created_nodes[nr_created_nodes++] = iter_node_flag;

        for (i = ja->tree_depth - 1; i >= (int) depth; i--) {
                dbg_printf("branch creation level %d, key %" PRIu64 "\n",
                                i, key >> (JA_BITS_PER_BYTE * (i - 2)));
                iter_dest_node_flag = NULL;
                ret = ja_node_set_nth(ja, &iter_dest_node_flag,
                        key >> (JA_BITS_PER_BYTE * (i - 2)),
                        iter_node_flag,
                        NULL);
                if (ret)
                        goto check_error;
                created_nodes[nr_created_nodes++] = iter_dest_node_flag;
                iter_node_flag = iter_dest_node_flag;
        }

        if (depth > 1) {
                /* We need to use set_nth on the previous level. */
                iter_dest_node_flag = node_flag;
                ret = ja_node_set_nth(ja, &iter_dest_node_flag,
                        key >> (JA_BITS_PER_BYTE * (depth - 2)),
                        iter_node_flag,
                        shadow_node);
                if (ret)
                        goto check_error;
                created_nodes[nr_created_nodes++] = iter_dest_node_flag;
                iter_node_flag = iter_dest_node_flag;
        }

        /* Publish new branch */
        dbg_printf("Publish branch %p, replacing %p\n",
                iter_node_flag, *node_flag_ptr);
        rcu_assign_pointer(*node_flag_ptr, iter_node_flag);

        /* Success */
        ret = 0;

check_error:
        if (ret) {
                for (i = 0; i < nr_created_nodes; i++) {
                        int tmpret;
                        int flags;

                        flags = RCUJA_SHADOW_CLEAR_FREE_LOCK;
                        if (i)
                                flags |= RCUJA_SHADOW_CLEAR_FREE_NODE;
                        tmpret = rcuja_shadow_clear(ja->ht,
                                        ja_node_ptr(created_nodes[i]),
                                        NULL,
                                        flags);
                        assert(!tmpret);
                }
        }
        if (parent_shadow_node)
                rcuja_shadow_unlock(parent_shadow_node);
unlock_shadow:
        if (shadow_node)
                rcuja_shadow_unlock(shadow_node);
end:
        return ret;
}

/*
 * Lock the hlist head shadow node mutex, and add node to list of
 * duplicates. Failure can happen if concurrent removal removes the last
 * node with same key before we get the lock.
 * Return 0 on success, negative error value on failure.
 */
static
int ja_chain_node(struct cds_ja *ja,
                struct cds_hlist_head *head,
                struct cds_ja_node *node)
{
        struct cds_ja_shadow_node *shadow_node;

        shadow_node = rcuja_shadow_lookup_lock(ja->ht,
                (struct cds_ja_inode *) head);
        if (!shadow_node)
                return -ENOENT;
        cds_hlist_add_head_rcu(&node->list, head);
        rcuja_shadow_unlock(shadow_node);
        return 0;
}

int cds_ja_add(struct cds_ja *ja, uint64_t key,
                struct cds_ja_node *new_node)
{
        unsigned int tree_depth, i;
        uint64_t iter_key;
        struct cds_ja_inode_flag **node_flag_ptr;       /* in parent */
        struct cds_ja_inode_flag *node_flag,
                *parent_node_flag,
                *parent2_node_flag;
        int ret;

        if (caa_unlikely(key > ja->key_max))
                return -EINVAL;
        tree_depth = ja->tree_depth;

retry:
        dbg_printf("cds_ja_add attempt: key %" PRIu64 ", node %p\n",
                key, new_node);
        iter_key = key;
        parent2_node_flag = NULL;
        parent_node_flag =
                (struct cds_ja_inode_flag *) &ja->root; /* Use root ptr address as key for mutex */
        node_flag_ptr = &ja->root;
        node_flag = rcu_dereference(*node_flag_ptr);

        /* Iterate on all internal levels */
        for (i = 1; i < tree_depth; i++) {
                if (!ja_node_ptr(node_flag)) {
                        ret = ja_attach_node(ja, node_flag_ptr,
                                        parent_node_flag, parent2_node_flag,
                                        key, i, new_node);
                        if (ret == -ENOENT || ret == -EEXIST)
                                goto retry;
                        else
                                goto end;
                }
                parent2_node_flag = parent_node_flag;
                parent_node_flag = node_flag;
                node_flag = ja_node_get_nth(node_flag,
                        &node_flag_ptr,
                        (unsigned char) iter_key);
                iter_key >>= JA_BITS_PER_BYTE;
        }

        /*
         * We reached bottom of tree, simply add node to last internal
         * level, or chain it if key is already present.
         */
        if (!ja_node_ptr(node_flag)) {
                ret = ja_attach_node(ja, node_flag_ptr, parent_node_flag,
                                parent2_node_flag, key, i, new_node);
        } else {
                ret = ja_chain_node(ja,
                        (struct cds_hlist_head *) ja_node_ptr(node_flag),
                        new_node);
        }
        if (ret == -ENOENT)
                goto retry;
end:
        return ret;
}

struct cds_ja *_cds_ja_new(unsigned int key_bits,
                const struct rcu_flavor_struct *flavor)
{
        struct cds_ja *ja;
        int ret;
        struct cds_ja_shadow_node *root_shadow_node;

        ja = calloc(sizeof(*ja), 1);
        if (!ja)
                goto ja_error;

        switch (key_bits) {
        case 8:
                ja->key_max = UINT8_MAX;
                break;
        case 16:
                ja->key_max = UINT16_MAX;
                break;
        case 32:
                ja->key_max = UINT32_MAX;
                break;
        case 64:
                ja->key_max = UINT64_MAX;
                break;
        default:
                goto check_error;
        }

        /* ja->root is NULL */
        /* tree_depth 0 is for pointer to root node */
        ja->tree_depth = (key_bits >> JA_BITS_PER_BYTE) + 1;
        assert(ja->tree_depth <= JA_MAX_DEPTH);
        ja->ht = rcuja_create_ht(flavor);
        if (!ja->ht)
                goto ht_error;

        /*
         * Note: we should not free this node until judy array destroy.
         */
        root_shadow_node = rcuja_shadow_set(ja->ht,
                        ja_node_ptr((struct cds_ja_inode_flag *) &ja->root),
                        NULL);
        if (!root_shadow_node) {
                ret = -ENOMEM;
                goto ht_node_error;
        }

        return ja;

ht_node_error:
        ret = rcuja_delete_ht(ja->ht);
        assert(!ret);
ht_error:
check_error:
        free(ja);
ja_error:
        return NULL;
}

/*
 * There should be no more concurrent add to the judy array while it is
 * being destroyed (ensured by the caller).
 */
int cds_ja_destroy(struct cds_ja *ja)
{
        int ret;

        rcuja_shadow_prune(ja->ht,
                RCUJA_SHADOW_CLEAR_FREE_NODE | RCUJA_SHADOW_CLEAR_FREE_LOCK);
        ret = rcuja_delete_ht(ja->ht);
        if (ret)
                return ret;
        if (uatomic_read(&ja->nr_fallback))
                fprintf(stderr,
                        "[warning] RCU Judy Array used %lu fallback node(s)\n",
                        uatomic_read(&ja->nr_fallback));
        free(ja);
        return 0;
}