xref: /freebsd/sys/contrib/ck/src/ck_ht.c (revision 74e9b5f29ad0056bbe11a30c91dfa0705fa19cd5)

/*
 * Copyright 2012-2015 Samy Al Bahra.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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 CK_HT_IM
#include <ck_ht.h>

/*
 * This implementation borrows several techniques from Josh Dybnis's
 * nbds library which can be found at http://code.google.com/p/nbds
 */
#include <ck_cc.h>
#include <ck_md.h>
#include <ck_pr.h>
#include <ck_stdint.h>
#include <ck_stdbool.h>
#include <ck_string.h>

#include "ck_ht_hash.h"
#include "ck_internal.h"

#ifndef CK_HT_BUCKET_LENGTH

#ifdef CK_HT_PP
#define CK_HT_BUCKET_SHIFT 2ULL
#else
#define CK_HT_BUCKET_SHIFT 1ULL
#endif

#define CK_HT_BUCKET_LENGTH (1U << CK_HT_BUCKET_SHIFT)
#define CK_HT_BUCKET_MASK (CK_HT_BUCKET_LENGTH - 1)
#endif

#ifndef CK_HT_PROBE_DEFAULT
#define CK_HT_PROBE_DEFAULT 64ULL
#endif

#if defined(CK_F_PR_LOAD_8) && defined(CK_F_PR_STORE_8)
#define CK_HT_WORD	    uint8_t
#define CK_HT_WORD_MAX	    UINT8_MAX
#define CK_HT_STORE(x, y)   ck_pr_store_8(x, y)
#define CK_HT_LOAD(x)	    ck_pr_load_8(x)
#elif defined(CK_F_PR_LOAD_16) && defined(CK_F_PR_STORE_16)
#define CK_HT_WORD	    uint16_t
#define CK_HT_WORD_MAX	    UINT16_MAX
#define CK_HT_STORE(x, y)   ck_pr_store_16(x, y)
#define CK_HT_LOAD(x)	    ck_pr_load_16(x)
#elif defined(CK_F_PR_LOAD_32) && defined(CK_F_PR_STORE_32)
#define CK_HT_WORD	    uint32_t
#define CK_HT_WORD_MAX	    UINT32_MAX
#define CK_HT_STORE(x, y)   ck_pr_store_32(x, y)
#define CK_HT_LOAD(x)	    ck_pr_load_32(x)
#else
#error "ck_ht is not supported on your platform."
#endif

struct ck_ht_map {
	unsigned int mode;
	CK_HT_TYPE deletions;
	CK_HT_TYPE probe_maximum;
	CK_HT_TYPE probe_length;
	CK_HT_TYPE probe_limit;
	CK_HT_TYPE size;
	CK_HT_TYPE n_entries;
	CK_HT_TYPE mask;
	CK_HT_TYPE capacity;
	CK_HT_TYPE step;
	CK_HT_WORD *probe_bound;
	struct ck_ht_entry *entries;
};

void
ck_ht_stat(struct ck_ht *table,
    struct ck_ht_stat *st)
{
	struct ck_ht_map *map = table->map;

	st->n_entries = map->n_entries;
	st->probe_maximum = map->probe_maximum;
	return;
}

void
ck_ht_hash(struct ck_ht_hash *h,
    struct ck_ht *table,
    const void *key,
    uint16_t key_length)
{

	table->h(h, key, key_length, table->seed);
	return;
}

void
ck_ht_hash_direct(struct ck_ht_hash *h,
    struct ck_ht *table,
    uintptr_t key)
{

	ck_ht_hash(h, table, &key, sizeof(key));
	return;
}

static void
ck_ht_hash_wrapper(struct ck_ht_hash *h,
    const void *key,
    size_t length,
    uint64_t seed)
{

	h->value = (unsigned long)MurmurHash64A(key, length, seed);
	return;
}

static struct ck_ht_map *
ck_ht_map_create(struct ck_ht *table, CK_HT_TYPE entries)
{
	struct ck_ht_map *map;
	CK_HT_TYPE size;
	uintptr_t prefix;
	uint32_t n_entries;

	n_entries = ck_internal_power_2(entries);
	if (n_entries < CK_HT_BUCKET_LENGTH)
		n_entries = CK_HT_BUCKET_LENGTH;

	size = sizeof(struct ck_ht_map) +
		   (sizeof(struct ck_ht_entry) * n_entries + CK_MD_CACHELINE - 1);

	if (table->mode & CK_HT_WORKLOAD_DELETE) {
		prefix = sizeof(CK_HT_WORD) * n_entries;
		size += prefix;
	} else {
		prefix = 0;
	}

	map = table->m->malloc(size);
	if (map == NULL)
		return NULL;

	map->mode = table->mode;
	map->size = size;
	map->probe_limit = ck_internal_max_64(n_entries >>
	    (CK_HT_BUCKET_SHIFT + 2), CK_HT_PROBE_DEFAULT);

	map->deletions = 0;
	map->probe_maximum = 0;
	map->capacity = n_entries;
	map->step = ck_cc_ffsll(map->capacity);
	map->mask = map->capacity - 1;
	map->n_entries = 0;
	map->entries = (struct ck_ht_entry *)(((uintptr_t)&map[1] + prefix +
	    CK_MD_CACHELINE - 1) & ~(CK_MD_CACHELINE - 1));

	if (table->mode & CK_HT_WORKLOAD_DELETE) {
		map->probe_bound = (CK_HT_WORD *)&map[1];
		memset(map->probe_bound, 0, prefix);
	} else {
		map->probe_bound = NULL;
	}

	memset(map->entries, 0, sizeof(struct ck_ht_entry) * n_entries);
	ck_pr_fence_store();
	return map;
}

static inline void
ck_ht_map_bound_set(struct ck_ht_map *m,
    struct ck_ht_hash h,
    CK_HT_TYPE n_probes)
{
	CK_HT_TYPE offset = h.value & m->mask;

	if (n_probes > m->probe_maximum)
		CK_HT_TYPE_STORE(&m->probe_maximum, n_probes);

	if (m->probe_bound != NULL && m->probe_bound[offset] < n_probes) {
		if (n_probes >= CK_HT_WORD_MAX)
			n_probes = CK_HT_WORD_MAX;

		CK_HT_STORE(&m->probe_bound[offset], n_probes);
		ck_pr_fence_store();
	}

	return;
}

static inline CK_HT_TYPE
ck_ht_map_bound_get(struct ck_ht_map *m, struct ck_ht_hash h)
{
	CK_HT_TYPE offset = h.value & m->mask;
	CK_HT_TYPE r = CK_HT_WORD_MAX;

	if (m->probe_bound != NULL) {
		r = CK_HT_LOAD(&m->probe_bound[offset]);
		if (r == CK_HT_WORD_MAX)
			r = CK_HT_TYPE_LOAD(&m->probe_maximum);
	} else {
		r = CK_HT_TYPE_LOAD(&m->probe_maximum);
	}

	return r;
}

static void
ck_ht_map_destroy(struct ck_malloc *m, struct ck_ht_map *map, bool defer)
{

	m->free(map, map->size, defer);
	return;
}

static inline size_t
ck_ht_map_probe_next(struct ck_ht_map *map, size_t offset, ck_ht_hash_t h, size_t probes)
{
	ck_ht_hash_t r;
	size_t stride;
	unsigned long level = (unsigned long)probes >> CK_HT_BUCKET_SHIFT;

	r.value = (h.value >> map->step) >> level;
	stride = (r.value & ~CK_HT_BUCKET_MASK) << 1
		     | (r.value & CK_HT_BUCKET_MASK);

	return (offset + level +
	    (stride | CK_HT_BUCKET_LENGTH)) & map->mask;
}

bool
ck_ht_init(struct ck_ht *table,
    unsigned int mode,
    ck_ht_hash_cb_t *h,
    struct ck_malloc *m,
    CK_HT_TYPE entries,
    uint64_t seed)
{

	if (m == NULL || m->malloc == NULL || m->free == NULL)
		return false;

	table->m = m;
	table->mode = mode;
	table->seed = seed;

	if (h == NULL) {
		table->h = ck_ht_hash_wrapper;
	} else {
		table->h = h;
	}

	table->map = ck_ht_map_create(table, entries);
	return table->map != NULL;
}

static struct ck_ht_entry *
ck_ht_map_probe_wr(struct ck_ht_map *map,
    ck_ht_hash_t h,
    ck_ht_entry_t *snapshot,
    ck_ht_entry_t **available,
    const void *key,
    uint16_t key_length,
    CK_HT_TYPE *probe_limit,
    CK_HT_TYPE *probe_wr)
{
	struct ck_ht_entry *bucket, *cursor;
	struct ck_ht_entry *first = NULL;
	size_t offset, i, j;
	CK_HT_TYPE probes = 0;
	CK_HT_TYPE limit;

	if (probe_limit == NULL) {
		limit = ck_ht_map_bound_get(map, h);
	} else {
		limit = CK_HT_TYPE_MAX;
	}

	offset = h.value & map->mask;
	for (i = 0; i < map->probe_limit; i++) {
		/*
		 * Probe on a complete cache line first. Scan forward and wrap around to
		 * the beginning of the cache line. Only when the complete cache line has
		 * been scanned do we move on to the next row.
		 */
		bucket = (void *)((uintptr_t)(map->entries + offset) &
			     ~(CK_MD_CACHELINE - 1));

		for (j = 0; j < CK_HT_BUCKET_LENGTH; j++) {
			uint16_t k;

			if (probes++ > limit)
				break;

			cursor = bucket + ((j + offset) & (CK_HT_BUCKET_LENGTH - 1));

			/*
			 * It is probably worth it to encapsulate probe state
			 * in order to prevent a complete reprobe sequence in
			 * the case of intermittent writers.
			 */
			if (cursor->key == CK_HT_KEY_TOMBSTONE) {
				if (first == NULL) {
					first = cursor;
					*probe_wr = probes;
				}

				continue;
			}

			if (cursor->key == CK_HT_KEY_EMPTY)
				goto leave;

			if (cursor->key == (uintptr_t)key)
				goto leave;

			if (map->mode & CK_HT_MODE_BYTESTRING) {
				void *pointer;

				/*
				 * Check memoized portion of hash value before
				 * expensive full-length comparison.
				 */
				k = ck_ht_entry_key_length(cursor);
				if (k != key_length)
					continue;

#ifdef CK_HT_PP
				if ((cursor->value >> CK_MD_VMA_BITS) != ((h.value >> 32) & CK_HT_KEY_MASK))
					continue;
#else
				if (cursor->hash != h.value)
					continue;
#endif

				pointer = ck_ht_entry_key(cursor);
				if (memcmp(pointer, key, key_length) == 0)
					goto leave;
			}
		}

		offset = ck_ht_map_probe_next(map, offset, h, probes);
	}

	cursor = NULL;

leave:
	if (probe_limit != NULL) {
		*probe_limit = probes;
	} else if (first == NULL) {
		*probe_wr = probes;
	}

	*available = first;

	if (cursor != NULL) {
		*snapshot = *cursor;
	}

	return cursor;
}

bool
ck_ht_gc(struct ck_ht *ht, unsigned long cycles, unsigned long seed)
{
	CK_HT_WORD *bounds = NULL;
	struct ck_ht_map *map = ht->map;
	CK_HT_TYPE maximum, i;
	CK_HT_TYPE size = 0;

	if (map->n_entries == 0) {
		CK_HT_TYPE_STORE(&map->probe_maximum, 0);
		if (map->probe_bound != NULL)
			memset(map->probe_bound, 0, sizeof(CK_HT_WORD) * map->capacity);

		return true;
	}

	if (cycles == 0) {
		maximum = 0;

		if (map->probe_bound != NULL) {
			size = sizeof(CK_HT_WORD) * map->capacity;
			bounds = ht->m->malloc(size);
			if (bounds == NULL)
				return false;

			memset(bounds, 0, size);
		}
	} else {
		maximum = map->probe_maximum;
	}

	for (i = 0; i < map->capacity; i++) {
		struct ck_ht_entry *entry, *priority, snapshot;
		struct ck_ht_hash h;
		CK_HT_TYPE probes_wr;
		CK_HT_TYPE offset;

		entry = &map->entries[(i + seed) & map->mask];
		if (entry->key == CK_HT_KEY_EMPTY ||
		    entry->key == CK_HT_KEY_TOMBSTONE) {
			continue;
		}

		if (ht->mode & CK_HT_MODE_BYTESTRING) {
#ifndef CK_HT_PP
			h.value = entry->hash;
#else
			ht->h(&h, ck_ht_entry_key(entry), ck_ht_entry_key_length(entry),
			    ht->seed);
#endif
			entry = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    ck_ht_entry_key(entry),
			    ck_ht_entry_key_length(entry),
			    NULL, &probes_wr);
		} else {
#ifndef CK_HT_PP
			h.value = entry->hash;
#else
			ht->h(&h, &entry->key, sizeof(entry->key), ht->seed);
#endif
			entry = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    (void *)entry->key,
			    sizeof(entry->key),
			    NULL, &probes_wr);
		}

		offset = h.value & map->mask;

		if (priority != NULL) {
			CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
			ck_pr_fence_store();
#ifndef CK_HT_PP
			CK_HT_TYPE_STORE(&priority->key_length, entry->key_length);
			CK_HT_TYPE_STORE(&priority->hash, entry->hash);
#endif
			ck_pr_store_ptr_unsafe(&priority->value, (void *)entry->value);
			ck_pr_fence_store();
			ck_pr_store_ptr_unsafe(&priority->key, (void *)entry->key);
			ck_pr_fence_store();
			CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
			ck_pr_fence_store();
			ck_pr_store_ptr_unsafe(&entry->key, (void *)CK_HT_KEY_TOMBSTONE);
			ck_pr_fence_store();
		}

		if (cycles == 0) {
			if (probes_wr > maximum)
				maximum = probes_wr;

			if (probes_wr >= CK_HT_WORD_MAX)
				probes_wr = CK_HT_WORD_MAX;

			if (bounds != NULL && probes_wr > bounds[offset])
				bounds[offset] = probes_wr;
		} else if (--cycles == 0)
			break;
	}

	if (maximum != map->probe_maximum)
		CK_HT_TYPE_STORE(&map->probe_maximum, maximum);

	if (bounds != NULL) {
		for (i = 0; i < map->capacity; i++)
			CK_HT_STORE(&map->probe_bound[i], bounds[i]);

		ht->m->free(bounds, size, false);
	}

	return true;
}

static struct ck_ht_entry *
ck_ht_map_probe_rd(struct ck_ht_map *map,
    ck_ht_hash_t h,
    ck_ht_entry_t *snapshot,
    const void *key,
    uint16_t key_length)
{
	struct ck_ht_entry *bucket, *cursor;
	size_t offset, i, j;
	CK_HT_TYPE probes = 0;
	CK_HT_TYPE probe_maximum;

#ifndef CK_HT_PP
	CK_HT_TYPE d = 0;
	CK_HT_TYPE d_prime = 0;
retry:
#endif

	probe_maximum = ck_ht_map_bound_get(map, h);
	offset = h.value & map->mask;

	for (i = 0; i < map->probe_limit; i++) {
		/*
		 * Probe on a complete cache line first. Scan forward and wrap around to
		 * the beginning of the cache line. Only when the complete cache line has
		 * been scanned do we move on to the next row.
		 */
		bucket = (void *)((uintptr_t)(map->entries + offset) &
			     ~(CK_MD_CACHELINE - 1));

		for (j = 0; j < CK_HT_BUCKET_LENGTH; j++) {
			uint16_t k;

			if (probes++ > probe_maximum)
				return NULL;

			cursor = bucket + ((j + offset) & (CK_HT_BUCKET_LENGTH - 1));

#ifdef CK_HT_PP
			snapshot->key = (uintptr_t)ck_pr_load_ptr(&cursor->key);
			ck_pr_fence_load();
			snapshot->value = (uintptr_t)ck_pr_load_ptr(&cursor->value);
#else
			d = CK_HT_TYPE_LOAD(&map->deletions);
			snapshot->key = (uintptr_t)ck_pr_load_ptr(&cursor->key);
			ck_pr_fence_load();
			snapshot->key_length = CK_HT_TYPE_LOAD(&cursor->key_length);
			snapshot->hash = CK_HT_TYPE_LOAD(&cursor->hash);
			snapshot->value = (uintptr_t)ck_pr_load_ptr(&cursor->value);
#endif

			/*
			 * It is probably worth it to encapsulate probe state
			 * in order to prevent a complete reprobe sequence in
			 * the case of intermittent writers.
			 */
			if (snapshot->key == CK_HT_KEY_TOMBSTONE)
				continue;

			if (snapshot->key == CK_HT_KEY_EMPTY)
				goto leave;

			if (snapshot->key == (uintptr_t)key)
				goto leave;

			if (map->mode & CK_HT_MODE_BYTESTRING) {
				void *pointer;

				/*
				 * Check memoized portion of hash value before
				 * expensive full-length comparison.
				 */
				k = ck_ht_entry_key_length(snapshot);
				if (k != key_length)
					continue;
#ifdef CK_HT_PP
				if ((snapshot->value >> CK_MD_VMA_BITS) != ((h.value >> 32) & CK_HT_KEY_MASK))
					continue;
#else
				if (snapshot->hash != h.value)
					continue;

				d_prime = CK_HT_TYPE_LOAD(&map->deletions);

				/*
				 * It is possible that the slot was
				 * replaced, initiate a re-probe.
				 */
				if (d != d_prime)
					goto retry;
#endif

				pointer = ck_ht_entry_key(snapshot);
				if (memcmp(pointer, key, key_length) == 0)
					goto leave;
			}
		}

		offset = ck_ht_map_probe_next(map, offset, h, probes);
	}

	return NULL;

leave:
	return cursor;
}

CK_HT_TYPE
ck_ht_count(struct ck_ht *table)
{
	struct ck_ht_map *map = ck_pr_load_ptr(&table->map);

	return CK_HT_TYPE_LOAD(&map->n_entries);
}

bool
ck_ht_next(struct ck_ht *table,
    struct ck_ht_iterator *i,
    struct ck_ht_entry **entry)
{
	struct ck_ht_map *map = table->map;
	uintptr_t key;

	if (i->offset >= map->capacity)
		return false;

	do {
		key = map->entries[i->offset].key;
		if (key != CK_HT_KEY_EMPTY && key != CK_HT_KEY_TOMBSTONE)
			break;
	} while (++i->offset < map->capacity);

	if (i->offset >= map->capacity)
		return false;

	*entry = map->entries + i->offset++;
	return true;
}

bool
ck_ht_reset_size_spmc(struct ck_ht *table, CK_HT_TYPE size)
{
	struct ck_ht_map *map, *update;

	map = table->map;
	update = ck_ht_map_create(table, size);
	if (update == NULL)
		return false;

	ck_pr_store_ptr_unsafe(&table->map, update);
	ck_ht_map_destroy(table->m, map, true);
	return true;
}

bool
ck_ht_reset_spmc(struct ck_ht *table)
{
	struct ck_ht_map *map = table->map;

	return ck_ht_reset_size_spmc(table, map->capacity);
}

bool
ck_ht_grow_spmc(struct ck_ht *table, CK_HT_TYPE capacity)
{
	struct ck_ht_map *map, *update;
	struct ck_ht_entry *bucket, *previous;
	struct ck_ht_hash h;
	size_t k, i, j, offset;
	CK_HT_TYPE probes;

restart:
	map = table->map;

	if (map->capacity >= capacity)
		return false;

	update = ck_ht_map_create(table, capacity);
	if (update == NULL)
		return false;

	for (k = 0; k < map->capacity; k++) {
		previous = &map->entries[k];

		if (previous->key == CK_HT_KEY_EMPTY || previous->key == CK_HT_KEY_TOMBSTONE)
			continue;

		if (table->mode & CK_HT_MODE_BYTESTRING) {
#ifdef CK_HT_PP
			void *key;
			uint16_t key_length;

			key = ck_ht_entry_key(previous);
			key_length = ck_ht_entry_key_length(previous);
#endif

#ifndef CK_HT_PP
			h.value = previous->hash;
#else
			table->h(&h, key, key_length, table->seed);
#endif
		} else {
#ifndef CK_HT_PP
			h.value = previous->hash;
#else
			table->h(&h, &previous->key, sizeof(previous->key), table->seed);
#endif
		}

		offset = h.value & update->mask;
		probes = 0;

		for (i = 0; i < update->probe_limit; i++) {
			bucket = (void *)((uintptr_t)(update->entries + offset) & ~(CK_MD_CACHELINE - 1));

			for (j = 0; j < CK_HT_BUCKET_LENGTH; j++) {
				struct ck_ht_entry *cursor = bucket + ((j + offset) & (CK_HT_BUCKET_LENGTH - 1));

				probes++;
				if (CK_CC_LIKELY(cursor->key == CK_HT_KEY_EMPTY)) {
					*cursor = *previous;
					update->n_entries++;
					ck_ht_map_bound_set(update, h, probes);
					break;
				}
			}

			if (j < CK_HT_BUCKET_LENGTH)
				break;

			offset = ck_ht_map_probe_next(update, offset, h, probes);
		}

		if (i == update->probe_limit) {
			/*
			 * We have hit the probe limit, the map needs to be even
			 * larger.
			 */
			ck_ht_map_destroy(table->m, update, false);
			capacity <<= 1;
			goto restart;
		}
	}

	ck_pr_fence_store();
	ck_pr_store_ptr_unsafe(&table->map, update);
	ck_ht_map_destroy(table->m, map, true);
	return true;
}

bool
ck_ht_remove_spmc(struct ck_ht *table,
    ck_ht_hash_t h,
    ck_ht_entry_t *entry)
{
	struct ck_ht_map *map;
	struct ck_ht_entry *candidate, snapshot;

	map = table->map;

	if (table->mode & CK_HT_MODE_BYTESTRING) {
		candidate = ck_ht_map_probe_rd(map, h, &snapshot,
		    ck_ht_entry_key(entry),
		    ck_ht_entry_key_length(entry));
	} else {
		candidate = ck_ht_map_probe_rd(map, h, &snapshot,
		    (void *)entry->key,
		    sizeof(entry->key));
	}

	/* No matching entry was found. */
	if (candidate == NULL || snapshot.key == CK_HT_KEY_EMPTY)
		return false;

	*entry = snapshot;

	ck_pr_store_ptr_unsafe(&candidate->key, (void *)CK_HT_KEY_TOMBSTONE);
	ck_pr_fence_store();
	CK_HT_TYPE_STORE(&map->n_entries, map->n_entries - 1);
	return true;
}

bool
ck_ht_get_spmc(struct ck_ht *table,
    ck_ht_hash_t h,
    ck_ht_entry_t *entry)
{
	struct ck_ht_entry *candidate, snapshot;
	struct ck_ht_map *map;
	CK_HT_TYPE d, d_prime;

restart:
	map = ck_pr_load_ptr(&table->map);

	/*
	 * Platforms that cannot read key and key_length atomically must reprobe
	 * on the scan of any single entry.
	 */
	d = CK_HT_TYPE_LOAD(&map->deletions);

	if (table->mode & CK_HT_MODE_BYTESTRING) {
		candidate = ck_ht_map_probe_rd(map, h, &snapshot,
		    ck_ht_entry_key(entry), ck_ht_entry_key_length(entry));
	} else {
		candidate = ck_ht_map_probe_rd(map, h, &snapshot,
		    (void *)entry->key, sizeof(entry->key));
	}

	d_prime = CK_HT_TYPE_LOAD(&map->deletions);
	if (d != d_prime) {
		/*
		 * It is possible we have read (K, V'). Only valid states are
		 * (K, V), (K', V') and (T, V). Restart load operation in face
		 * of concurrent deletions or replacements.
		 */
		goto restart;
	}

	if (candidate == NULL || snapshot.key == CK_HT_KEY_EMPTY)
		return false;

	*entry = snapshot;
	return true;
}

bool
ck_ht_set_spmc(struct ck_ht *table,
    ck_ht_hash_t h,
    ck_ht_entry_t *entry)
{
	struct ck_ht_entry snapshot, *candidate, *priority;
	struct ck_ht_map *map;
	CK_HT_TYPE probes, probes_wr;
	bool empty = false;

	for (;;) {
		map = table->map;

		if (table->mode & CK_HT_MODE_BYTESTRING) {
			candidate = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    ck_ht_entry_key(entry),
			    ck_ht_entry_key_length(entry),
			    &probes, &probes_wr);
		} else {
			candidate = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    (void *)entry->key,
			    sizeof(entry->key),
			    &probes, &probes_wr);
		}

		if (priority != NULL) {
			probes = probes_wr;
			break;
		}

		if (candidate != NULL)
			break;

		if (ck_ht_grow_spmc(table, map->capacity << 1) == false)
			return false;
	}

	if (candidate == NULL) {
		candidate = priority;
		empty = true;
	}

	if (candidate->key != CK_HT_KEY_EMPTY &&
	    priority != NULL && candidate != priority) {
		/*
		 * Entry is moved into another position in probe sequence.
		 * We avoid a state of (K, B) (where [K, B] -> [K', B]) by
		 * guaranteeing a forced reprobe before transitioning from K to
		 * T. (K, B) implies (K, B, D') so we will reprobe successfully
		 * from this transient state.
		 */
		probes = probes_wr;

#ifndef CK_HT_PP
		CK_HT_TYPE_STORE(&priority->key_length, entry->key_length);
		CK_HT_TYPE_STORE(&priority->hash, entry->hash);
#endif

		/*
		 * Readers must observe version counter change before they
		 * observe re-use. If they observe re-use, it is at most
		 * a tombstone.
		 */
		if (priority->value == CK_HT_KEY_TOMBSTONE) {
			CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
			ck_pr_fence_store();
		}

		ck_pr_store_ptr_unsafe(&priority->value, (void *)entry->value);
		ck_pr_fence_store();
		ck_pr_store_ptr_unsafe(&priority->key, (void *)entry->key);
		ck_pr_fence_store();

		/*
		 * Make sure that readers who observe the tombstone would
		 * also observe counter change.
		 */
		CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
		ck_pr_fence_store();

		ck_pr_store_ptr_unsafe(&candidate->key, (void *)CK_HT_KEY_TOMBSTONE);
		ck_pr_fence_store();
	} else {
		/*
		 * In this case we are inserting a new entry or replacing
		 * an existing entry. Yes, this can be combined into above branch,
		 * but isn't because you are actually looking at dying code
		 * (ck_ht is effectively deprecated and is being replaced soon).
		 */
		bool replace = candidate->key != CK_HT_KEY_EMPTY &&
		    candidate->key != CK_HT_KEY_TOMBSTONE;

		if (priority != NULL) {
			if (priority->key == CK_HT_KEY_TOMBSTONE) {
				CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
				ck_pr_fence_store();
			}

			candidate = priority;
			probes = probes_wr;
		}

#ifdef CK_HT_PP
		ck_pr_store_ptr_unsafe(&candidate->value, (void *)entry->value);
		ck_pr_fence_store();
		ck_pr_store_ptr_unsafe(&candidate->key, (void *)entry->key);
#else
		CK_HT_TYPE_STORE(&candidate->key_length, entry->key_length);
		CK_HT_TYPE_STORE(&candidate->hash, entry->hash);
		ck_pr_store_ptr_unsafe(&candidate->value, (void *)entry->value);
		ck_pr_fence_store();
		ck_pr_store_ptr_unsafe(&candidate->key, (void *)entry->key);
#endif

		/*
		 * If we are insert a new entry then increment number
		 * of entries associated with map.
		 */
		if (replace == false)
			CK_HT_TYPE_STORE(&map->n_entries, map->n_entries + 1);
	}

	ck_ht_map_bound_set(map, h, probes);

	/* Enforce a load factor of 0.5. */
	if (map->n_entries * 2 > map->capacity)
		ck_ht_grow_spmc(table, map->capacity << 1);

	if (empty == true) {
		entry->key = CK_HT_KEY_EMPTY;
	} else {
		*entry = snapshot;
	}

	return true;
}

bool
ck_ht_put_spmc(struct ck_ht *table,
    ck_ht_hash_t h,
    ck_ht_entry_t *entry)
{
	struct ck_ht_entry snapshot, *candidate, *priority;
	struct ck_ht_map *map;
	CK_HT_TYPE probes, probes_wr;

	for (;;) {
		map = table->map;

		if (table->mode & CK_HT_MODE_BYTESTRING) {
			candidate = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    ck_ht_entry_key(entry),
			    ck_ht_entry_key_length(entry),
			    &probes, &probes_wr);
		} else {
			candidate = ck_ht_map_probe_wr(map, h, &snapshot, &priority,
			    (void *)entry->key,
			    sizeof(entry->key),
			    &probes, &probes_wr);
		}

		if (candidate != NULL || priority != NULL)
			break;

		if (ck_ht_grow_spmc(table, map->capacity << 1) == false)
			return false;
	}

	if (priority != NULL) {
		/* Version counter is updated before re-use. */
		CK_HT_TYPE_STORE(&map->deletions, map->deletions + 1);
		ck_pr_fence_store();

		/* Re-use tombstone if one was found. */
		candidate = priority;
		probes = probes_wr;
	} else if (candidate->key != CK_HT_KEY_EMPTY &&
	    candidate->key != CK_HT_KEY_TOMBSTONE) {
		/*
		 * If the snapshot key is non-empty and the value field is not
		 * a tombstone then an identical key was found. As store does
		 * not implement replacement, we will fail.
		 */
		return false;
	}

	ck_ht_map_bound_set(map, h, probes);

#ifdef CK_HT_PP
	ck_pr_store_ptr_unsafe(&candidate->value, (void *)entry->value);
	ck_pr_fence_store();
	ck_pr_store_ptr_unsafe(&candidate->key, (void *)entry->key);
#else
	CK_HT_TYPE_STORE(&candidate->key_length, entry->key_length);
	CK_HT_TYPE_STORE(&candidate->hash, entry->hash);
	ck_pr_store_ptr_unsafe(&candidate->value, (void *)entry->value);
	ck_pr_fence_store();
	ck_pr_store_ptr_unsafe(&candidate->key, (void *)entry->key);
#endif

	CK_HT_TYPE_STORE(&map->n_entries, map->n_entries + 1);

	/* Enforce a load factor of 0.5. */
	if (map->n_entries * 2 > map->capacity)
		ck_ht_grow_spmc(table, map->capacity << 1);

	return true;
}

void
ck_ht_destroy(struct ck_ht *table)
{

	ck_ht_map_destroy(table->m, table->map, false);
	return;
}