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redis/src/dict.c

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/* Hash Tables Implementation.
*
* This file implements in memory hash tables with insert/del/replace/find/
* get-random-element operations. Hash tables will auto resize if needed
* tables of power of two in size are used, collisions are handled by
* chaining. See the source code for more information... :)
*
* Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* 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 Redis 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.
*/
#include "fmacros.h"
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <stdarg.h>
#include <limits.h>
#include <sys/time.h>
#include "dict.h"
#include "zmalloc.h"
#include "redisassert.h"
/* Using dictEnableResize() / dictDisableResize() we make possible to
* enable/disable resizing of the hash table as needed. This is very important
* for Redis, as we use copy-on-write and don't want to move too much memory
* around when there is a child performing saving operations.
*
* Note that even when dict_can_resize is set to 0, not all resizes are
* prevented: a hash table is still allowed to grow if the ratio between
* the number of elements and the buckets > dict_force_resize_ratio. */
static int dict_can_resize = 1;
static unsigned int dict_force_resize_ratio = 5;
/* -------------------------- private prototypes ---------------------------- */
static int _dictExpandIfNeeded(dict *d);
static signed char _dictNextExp(unsigned long size);
static long _dictKeyIndex(dict *d, const void *key, uint64_t hash, dictEntry **existing);
static int _dictInit(dict *d, dictType *type);
/* -------------------------- hash functions -------------------------------- */
static uint8_t dict_hash_function_seed[16];
void dictSetHashFunctionSeed(uint8_t *seed) {
memcpy(dict_hash_function_seed,seed,sizeof(dict_hash_function_seed));
}
uint8_t *dictGetHashFunctionSeed(void) {
return dict_hash_function_seed;
}
/* The default hashing function uses SipHash implementation
* in siphash.c. */
uint64_t siphash(const uint8_t *in, const size_t inlen, const uint8_t *k);
uint64_t siphash_nocase(const uint8_t *in, const size_t inlen, const uint8_t *k);
uint64_t dictGenHashFunction(const void *key, int len) {
return siphash(key,len,dict_hash_function_seed);
}
uint64_t dictGenCaseHashFunction(const unsigned char *buf, int len) {
return siphash_nocase(buf,len,dict_hash_function_seed);
}
/* ----------------------------- API implementation ------------------------- */
/* Reset a hash table already initialized with ht_init().
* NOTE: This function should only be called by ht_destroy(). */
static void _dictReset(dict *d, int htidx)
{
d->ht_table[htidx] = NULL;
d->ht_size_exp[htidx] = -1;
d->ht_used[htidx] = 0;
}
/* Create a new hash table */
dict *dictCreate(dictType *type)
{
dict *d = zmalloc(sizeof(*d));
_dictInit(d,type);
return d;
}
/* Initialize the hash table */
int _dictInit(dict *d, dictType *type)
{
_dictReset(d, 0);
_dictReset(d, 1);
d->type = type;
d->rehashidx = -1;
d->pauserehash = 0;
return DICT_OK;
}
/* Resize the table to the minimal size that contains all the elements,
* but with the invariant of a USED/BUCKETS ratio near to <= 1 */
int dictResize(dict *d)
{
unsigned long minimal;
if (!dict_can_resize || dictIsRehashing(d)) return DICT_ERR;
minimal = d->ht_used[0];
if (minimal < DICT_HT_INITIAL_SIZE)
minimal = DICT_HT_INITIAL_SIZE;
return dictExpand(d, minimal);
}
/* Expand or create the hash table,
* when malloc_failed is non-NULL, it'll avoid panic if malloc fails (in which case it'll be set to 1).
* Returns DICT_OK if expand was performed, and DICT_ERR if skipped. */
int _dictExpand(dict *d, unsigned long size, int* malloc_failed)
{
if (malloc_failed) *malloc_failed = 0;
/* the size is invalid if it is smaller than the number of
* elements already inside the hash table */
if (dictIsRehashing(d) || d->ht_used[0] > size)
return DICT_ERR;
/* the new hash table */
dictEntry **new_ht_table;
unsigned long new_ht_used;
signed char new_ht_size_exp = _dictNextExp(size);
/* Detect overflows */
size_t newsize = 1ul<<new_ht_size_exp;
if (newsize < size || newsize * sizeof(dictEntry*) < newsize)
return DICT_ERR;
/* Rehashing to the same table size is not useful. */
if (new_ht_size_exp == d->ht_size_exp[0]) return DICT_ERR;
/* Allocate the new hash table and initialize all pointers to NULL */
if (malloc_failed) {
new_ht_table = ztrycalloc(newsize*sizeof(dictEntry*));
*malloc_failed = new_ht_table == NULL;
if (*malloc_failed)
return DICT_ERR;
} else
new_ht_table = zcalloc(newsize*sizeof(dictEntry*));
new_ht_used = 0;
/* Is this the first initialization? If so it's not really a rehashing
* we just set the first hash table so that it can accept keys. */
if (d->ht_table[0] == NULL) {
d->ht_size_exp[0] = new_ht_size_exp;
d->ht_used[0] = new_ht_used;
d->ht_table[0] = new_ht_table;
return DICT_OK;
}
/* Prepare a second hash table for incremental rehashing */
d->ht_size_exp[1] = new_ht_size_exp;
d->ht_used[1] = new_ht_used;
d->ht_table[1] = new_ht_table;
d->rehashidx = 0;
return DICT_OK;
}
/* return DICT_ERR if expand was not performed */
int dictExpand(dict *d, unsigned long size) {
return _dictExpand(d, size, NULL);
}
/* return DICT_ERR if expand failed due to memory allocation failure */
int dictTryExpand(dict *d, unsigned long size) {
int malloc_failed;
_dictExpand(d, size, &malloc_failed);
return malloc_failed? DICT_ERR : DICT_OK;
}
/* Performs N steps of incremental rehashing. Returns 1 if there are still
* keys to move from the old to the new hash table, otherwise 0 is returned.
*
* Note that a rehashing step consists in moving a bucket (that may have more
* than one key as we use chaining) from the old to the new hash table, however
* since part of the hash table may be composed of empty spaces, it is not
* guaranteed that this function will rehash even a single bucket, since it
* will visit at max N*10 empty buckets in total, otherwise the amount of
* work it does would be unbound and the function may block for a long time. */
int dictRehash(dict *d, int n) {
int empty_visits = n*10; /* Max number of empty buckets to visit. */
if (!dictIsRehashing(d)) return 0;
while(n-- && d->ht_used[0] != 0) {
dictEntry *de, *nextde;
/* Note that rehashidx can't overflow as we are sure there are more
* elements because ht[0].used != 0 */
assert(DICTHT_SIZE(d->ht_size_exp[0]) > (unsigned long)d->rehashidx);
while(d->ht_table[0][d->rehashidx] == NULL) {
d->rehashidx++;
if (--empty_visits == 0) return 1;
}
de = d->ht_table[0][d->rehashidx];
/* Move all the keys in this bucket from the old to the new hash HT */
while(de) {
uint64_t h;
nextde = de->next;
/* Get the index in the new hash table */
h = dictHashKey(d, de->key) & DICTHT_SIZE_MASK(d->ht_size_exp[1]);
de->next = d->ht_table[1][h];
d->ht_table[1][h] = de;
d->ht_used[0]--;
d->ht_used[1]++;
de = nextde;
}
d->ht_table[0][d->rehashidx] = NULL;
d->rehashidx++;
}
/* Check if we already rehashed the whole table... */
if (d->ht_used[0] == 0) {
zfree(d->ht_table[0]);
/* Copy the new ht onto the old one */
d->ht_table[0] = d->ht_table[1];
d->ht_used[0] = d->ht_used[1];
d->ht_size_exp[0] = d->ht_size_exp[1];
_dictReset(d, 1);
d->rehashidx = -1;
return 0;
}
/* More to rehash... */
return 1;
}
long long timeInMilliseconds(void) {
struct timeval tv;
gettimeofday(&tv,NULL);
return (((long long)tv.tv_sec)*1000)+(tv.tv_usec/1000);
}
/* Rehash in ms+"delta" milliseconds. The value of "delta" is larger
* than 0, and is smaller than 1 in most cases. The exact upper bound
* depends on the running time of dictRehash(d,100).*/
int dictRehashMilliseconds(dict *d, int ms) {
if (d->pauserehash > 0) return 0;
long long start = timeInMilliseconds();
int rehashes = 0;
while(dictRehash(d,100)) {
rehashes += 100;
if (timeInMilliseconds()-start > ms) break;
}
return rehashes;
}
/* This function performs just a step of rehashing, and only if hashing has
* not been paused for our hash table. When we have iterators in the
* middle of a rehashing we can't mess with the two hash tables otherwise
* some element can be missed or duplicated.
*
* This function is called by common lookup or update operations in the
* dictionary so that the hash table automatically migrates from H1 to H2
* while it is actively used. */
static void _dictRehashStep(dict *d) {
if (d->pauserehash == 0) dictRehash(d,1);
}
/* Add an element to the target hash table */
int dictAdd(dict *d, void *key, void *val)
{
dictEntry *entry = dictAddRaw(d,key,NULL);
if (!entry) return DICT_ERR;
dictSetVal(d, entry, val);
return DICT_OK;
}
/* Low level add or find:
* This function adds the entry but instead of setting a value returns the
* dictEntry structure to the user, that will make sure to fill the value
* field as they wish.
*
* This function is also directly exposed to the user API to be called
* mainly in order to store non-pointers inside the hash value, example:
*
* entry = dictAddRaw(dict,mykey,NULL);
* if (entry != NULL) dictSetSignedIntegerVal(entry,1000);
*
* Return values:
*
* If key already exists NULL is returned, and "*existing" is populated
* with the existing entry if existing is not NULL.
*
* If key was added, the hash entry is returned to be manipulated by the caller.
*/
dictEntry *dictAddRaw(dict *d, void *key, dictEntry **existing)
{
long index;
dictEntry *entry;
int htidx;
if (dictIsRehashing(d)) _dictRehashStep(d);
/* Get the index of the new element, or -1 if
* the element already exists. */
if ((index = _dictKeyIndex(d, key, dictHashKey(d,key), existing)) == -1)
return NULL;
/* Allocate the memory and store the new entry.
* Insert the element in top, with the assumption that in a database
* system it is more likely that recently added entries are accessed
* more frequently. */
htidx = dictIsRehashing(d) ? 1 : 0;
size_t metasize = dictMetadataSize(d);
entry = zmalloc(sizeof(*entry) + metasize);
if (metasize > 0) {
memset(dictMetadata(entry), 0, metasize);
}
entry->next = d->ht_table[htidx][index];
d->ht_table[htidx][index] = entry;
d->ht_used[htidx]++;
/* Set the hash entry fields. */
dictSetKey(d, entry, key);
return entry;
}
/* Add or Overwrite:
* Add an element, discarding the old value if the key already exists.
* Return 1 if the key was added from scratch, 0 if there was already an
* element with such key and dictReplace() just performed a value update
* operation. */
int dictReplace(dict *d, void *key, void *val)
{
dictEntry *entry, *existing, auxentry;
/* Try to add the element. If the key
* does not exists dictAdd will succeed. */
entry = dictAddRaw(d,key,&existing);
if (entry) {
dictSetVal(d, entry, val);
return 1;
}
/* Set the new value and free the old one. Note that it is important
* to do that in this order, as the value may just be exactly the same
* as the previous one. In this context, think to reference counting,
* you want to increment (set), and then decrement (free), and not the
* reverse. */
auxentry = *existing;
dictSetVal(d, existing, val);
dictFreeVal(d, &auxentry);
return 0;
}
/* Add or Find:
* dictAddOrFind() is simply a version of dictAddRaw() that always
* returns the hash entry of the specified key, even if the key already
* exists and can't be added (in that case the entry of the already
* existing key is returned.)
*
* See dictAddRaw() for more information. */
dictEntry *dictAddOrFind(dict *d, void *key) {
dictEntry *entry, *existing;
entry = dictAddRaw(d,key,&existing);
return entry ? entry : existing;
}
/* Search and remove an element. This is a helper function for
* dictDelete() and dictUnlink(), please check the top comment
* of those functions. */
static dictEntry *dictGenericDelete(dict *d, const void *key, int nofree) {
uint64_t h, idx;
dictEntry *he, *prevHe;
int table;
/* dict is empty */
if (dictSize(d) == 0) return NULL;
if (dictIsRehashing(d)) _dictRehashStep(d);
h = dictHashKey(d, key);
for (table = 0; table <= 1; table++) {
idx = h & DICTHT_SIZE_MASK(d->ht_size_exp[table]);
he = d->ht_table[table][idx];
prevHe = NULL;
while(he) {
if (key==he->key || dictCompareKeys(d, key, he->key)) {
/* Unlink the element from the list */
if (prevHe)
prevHe->next = he->next;
else
d->ht_table[table][idx] = he->next;
if (!nofree) {
dictFreeUnlinkedEntry(d, he);
}
d->ht_used[table]--;
return he;
}
prevHe = he;
he = he->next;
}
if (!dictIsRehashing(d)) break;
}
return NULL; /* not found */
}
/* Remove an element, returning DICT_OK on success or DICT_ERR if the
* element was not found. */
int dictDelete(dict *ht, const void *key) {
return dictGenericDelete(ht,key,0) ? DICT_OK : DICT_ERR;
}
/* Remove an element from the table, but without actually releasing
* the key, value and dictionary entry. The dictionary entry is returned
* if the element was found (and unlinked from the table), and the user
* should later call `dictFreeUnlinkedEntry()` with it in order to release it.
* Otherwise if the key is not found, NULL is returned.
*
* This function is useful when we want to remove something from the hash
* table but want to use its value before actually deleting the entry.
* Without this function the pattern would require two lookups:
*
* entry = dictFind(...);
* // Do something with entry
* dictDelete(dictionary,entry);
*
* Thanks to this function it is possible to avoid this, and use
* instead:
*
* entry = dictUnlink(dictionary,entry);
* // Do something with entry
* dictFreeUnlinkedEntry(entry); // <- This does not need to lookup again.
*/
dictEntry *dictUnlink(dict *d, const void *key) {
return dictGenericDelete(d,key,1);
}
/* You need to call this function to really free the entry after a call
* to dictUnlink(). It's safe to call this function with 'he' = NULL. */
void dictFreeUnlinkedEntry(dict *d, dictEntry *he) {
if (he == NULL) return;
dictFreeKey(d, he);
dictFreeVal(d, he);
zfree(he);
}
/* Destroy an entire dictionary */
int _dictClear(dict *d, int htidx, void(callback)(dict*)) {
unsigned long i;
/* Free all the elements */
for (i = 0; i < DICTHT_SIZE(d->ht_size_exp[htidx]) && d->ht_used[htidx] > 0; i++) {
dictEntry *he, *nextHe;
if (callback && (i & 65535) == 0) callback(d);
if ((he = d->ht_table[htidx][i]) == NULL) continue;
while(he) {
nextHe = he->next;
dictFreeKey(d, he);
dictFreeVal(d, he);
zfree(he);
d->ht_used[htidx]--;
he = nextHe;
}
}
/* Free the table and the allocated cache structure */
zfree(d->ht_table[htidx]);
/* Re-initialize the table */
_dictReset(d, htidx);
return DICT_OK; /* never fails */
}
/* Clear & Release the hash table */
void dictRelease(dict *d)
{
_dictClear(d,0,NULL);
_dictClear(d,1,NULL);
zfree(d);
}
dictEntry *dictFind(dict *d, const void *key)
{
dictEntry *he;
uint64_t h, idx, table;
if (dictSize(d) == 0) return NULL; /* dict is empty */
if (dictIsRehashing(d)) _dictRehashStep(d);
h = dictHashKey(d, key);
for (table = 0; table <= 1; table++) {
idx = h & DICTHT_SIZE_MASK(d->ht_size_exp[table]);
he = d->ht_table[table][idx];
while(he) {
if (key==he->key || dictCompareKeys(d, key, he->key))
return he;
he = he->next;
}
if (!dictIsRehashing(d)) return NULL;
}
return NULL;
}
void *dictFetchValue(dict *d, const void *key) {
dictEntry *he;
he = dictFind(d,key);
return he ? dictGetVal(he) : NULL;
}
/* A fingerprint is a 64 bit number that represents the state of the dictionary
* at a given time, it's just a few dict properties xored together.
* When an unsafe iterator is initialized, we get the dict fingerprint, and check
* the fingerprint again when the iterator is released.
* If the two fingerprints are different it means that the user of the iterator
* performed forbidden operations against the dictionary while iterating. */
unsigned long long dictFingerprint(dict *d) {
unsigned long long integers[6], hash = 0;
int j;
integers[0] = (long) d->ht_table[0];
integers[1] = d->ht_size_exp[0];
integers[2] = d->ht_used[0];
integers[3] = (long) d->ht_table[1];
integers[4] = d->ht_size_exp[1];
integers[5] = d->ht_used[1];
/* We hash N integers by summing every successive integer with the integer
* hashing of the previous sum. Basically:
*
* Result = hash(hash(hash(int1)+int2)+int3) ...
*
* This way the same set of integers in a different order will (likely) hash
* to a different number. */
for (j = 0; j < 6; j++) {
hash += integers[j];
/* For the hashing step we use Tomas Wang's 64 bit integer hash. */
hash = (~hash) + (hash << 21); // hash = (hash << 21) - hash - 1;
hash = hash ^ (hash >> 24);
hash = (hash + (hash << 3)) + (hash << 8); // hash * 265
hash = hash ^ (hash >> 14);
hash = (hash + (hash << 2)) + (hash << 4); // hash * 21
hash = hash ^ (hash >> 28);
hash = hash + (hash << 31);
}
return hash;
}
dictIterator *dictGetIterator(dict *d)
{
dictIterator *iter = zmalloc(sizeof(*iter));
iter->d = d;
iter->table = 0;
iter->index = -1;
iter->safe = 0;
iter->entry = NULL;
iter->nextEntry = NULL;
return iter;
}
dictIterator *dictGetSafeIterator(dict *d) {
dictIterator *i = dictGetIterator(d);
i->safe = 1;
return i;
}
dictEntry *dictNext(dictIterator *iter)
{
while (1) {
if (iter->entry == NULL) {
if (iter->index == -1 && iter->table == 0) {
if (iter->safe)
dictPauseRehashing(iter->d);
else
iter->fingerprint = dictFingerprint(iter->d);
}
iter->index++;
if (iter->index >= (long) DICTHT_SIZE(iter->d->ht_size_exp[iter->table])) {
if (dictIsRehashing(iter->d) && iter->table == 0) {
iter->table++;
iter->index = 0;
} else {
break;
}
}
iter->entry = iter->d->ht_table[iter->table][iter->index];
} else {
iter->entry = iter->nextEntry;
}
if (iter->entry) {
/* We need to save the 'next' here, the iterator user
* may delete the entry we are returning. */
iter->nextEntry = iter->entry->next;
return iter->entry;
}
}
return NULL;
}
void dictReleaseIterator(dictIterator *iter)
{
if (!(iter->index == -1 && iter->table == 0)) {
if (iter->safe)
dictResumeRehashing(iter->d);
else
assert(iter->fingerprint == dictFingerprint(iter->d));
}
zfree(iter);
}
/* Return a random entry from the hash table. Useful to
* implement randomized algorithms */
dictEntry *dictGetRandomKey(dict *d)
{
dictEntry *he, *orighe;
unsigned long h;
int listlen, listele;
if (dictSize(d) == 0) return NULL;
if (dictIsRehashing(d)) _dictRehashStep(d);
if (dictIsRehashing(d)) {
unsigned long s0 = DICTHT_SIZE(d->ht_size_exp[0]);
do {
/* We are sure there are no elements in indexes from 0
* to rehashidx-1 */
h = d->rehashidx + (randomULong() % (dictSlots(d) - d->rehashidx));
he = (h >= s0) ? d->ht_table[1][h - s0] : d->ht_table[0][h];
} while(he == NULL);
} else {
unsigned long m = DICTHT_SIZE_MASK(d->ht_size_exp[0]);
do {
h = randomULong() & m;
he = d->ht_table[0][h];
} while(he == NULL);
}
/* Now we found a non empty bucket, but it is a linked
* list and we need to get a random element from the list.
* The only sane way to do so is counting the elements and
* select a random index. */
listlen = 0;
orighe = he;
while(he) {
he = he->next;
listlen++;
}
listele = random() % listlen;
he = orighe;
while(listele--) he = he->next;
return he;
}
/* This function samples the dictionary to return a few keys from random
* locations.
*
* It does not guarantee to return all the keys specified in 'count', nor
* it does guarantee to return non-duplicated elements, however it will make
* some effort to do both things.
*
* Returned pointers to hash table entries are stored into 'des' that
* points to an array of dictEntry pointers. The array must have room for
* at least 'count' elements, that is the argument we pass to the function
* to tell how many random elements we need.
*
* The function returns the number of items stored into 'des', that may
* be less than 'count' if the hash table has less than 'count' elements
* inside, or if not enough elements were found in a reasonable amount of
* steps.
*
* Note that this function is not suitable when you need a good distribution
* of the returned items, but only when you need to "sample" a given number
* of continuous elements to run some kind of algorithm or to produce
* statistics. However the function is much faster than dictGetRandomKey()
* at producing N elements. */
unsigned int dictGetSomeKeys(dict *d, dictEntry **des, unsigned int count) {
unsigned long j; /* internal hash table id, 0 or 1. */
unsigned long tables; /* 1 or 2 tables? */
unsigned long stored = 0, maxsizemask;
unsigned long maxsteps;
if (dictSize(d) < count) count = dictSize(d);
maxsteps = count*10;
/* Try to do a rehashing work proportional to 'count'. */
for (j = 0; j < count; j++) {
if (dictIsRehashing(d))
_dictRehashStep(d);
else
break;
}
tables = dictIsRehashing(d) ? 2 : 1;
maxsizemask = DICTHT_SIZE_MASK(d->ht_size_exp[0]);
if (tables > 1 && maxsizemask < DICTHT_SIZE_MASK(d->ht_size_exp[1]))
maxsizemask = DICTHT_SIZE_MASK(d->ht_size_exp[1]);
/* Pick a random point inside the larger table. */
unsigned long i = randomULong() & maxsizemask;
unsigned long emptylen = 0; /* Continuous empty entries so far. */
while(stored < count && maxsteps--) {
for (j = 0; j < tables; j++) {
/* Invariant of the dict.c rehashing: up to the indexes already
* visited in ht[0] during the rehashing, there are no populated
* buckets, so we can skip ht[0] for indexes between 0 and idx-1. */
if (tables == 2 && j == 0 && i < (unsigned long) d->rehashidx) {
/* Moreover, if we are currently out of range in the second
* table, there will be no elements in both tables up to
* the current rehashing index, so we jump if possible.
* (this happens when going from big to small table). */
if (i >= DICTHT_SIZE(d->ht_size_exp[1]))
i = d->rehashidx;
else
continue;
}
if (i >= DICTHT_SIZE(d->ht_size_exp[j])) continue; /* Out of range for this table. */
dictEntry *he = d->ht_table[j][i];
/* Count contiguous empty buckets, and jump to other
* locations if they reach 'count' (with a minimum of 5). */
if (he == NULL) {
emptylen++;
if (emptylen >= 5 && emptylen > count) {
i = randomULong() & maxsizemask;
emptylen = 0;
}
} else {
emptylen = 0;
while (he) {
/* Collect all the elements of the buckets found non
* empty while iterating. */
*des = he;
des++;
he = he->next;
stored++;
if (stored == count) return stored;
}
}
}
i = (i+1) & maxsizemask;
}
return stored;
}
/* This is like dictGetRandomKey() from the POV of the API, but will do more
* work to ensure a better distribution of the returned element.
*
* This function improves the distribution because the dictGetRandomKey()
* problem is that it selects a random bucket, then it selects a random
* element from the chain in the bucket. However elements being in different
* chain lengths will have different probabilities of being reported. With
* this function instead what we do is to consider a "linear" range of the table
* that may be constituted of N buckets with chains of different lengths
* appearing one after the other. Then we report a random element in the range.
* In this way we smooth away the problem of different chain lengths. */
#define GETFAIR_NUM_ENTRIES 15
dictEntry *dictGetFairRandomKey(dict *d) {
dictEntry *entries[GETFAIR_NUM_ENTRIES];
unsigned int count = dictGetSomeKeys(d,entries,GETFAIR_NUM_ENTRIES);
/* Note that dictGetSomeKeys() may return zero elements in an unlucky
* run() even if there are actually elements inside the hash table. So
* when we get zero, we call the true dictGetRandomKey() that will always
* yield the element if the hash table has at least one. */
if (count == 0) return dictGetRandomKey(d);
unsigned int idx = rand() % count;
return entries[idx];
}
/* Function to reverse bits. Algorithm from:
* http://graphics.stanford.edu/~seander/bithacks.html#ReverseParallel */
static unsigned long rev(unsigned long v) {
unsigned long s = CHAR_BIT * sizeof(v); // bit size; must be power of 2
unsigned long mask = ~0UL;
while ((s >>= 1) > 0) {
mask ^= (mask << s);
v = ((v >> s) & mask) | ((v << s) & ~mask);
}
return v;
}
/* dictScan() is used to iterate over the elements of a dictionary.
*
* Iterating works the following way:
*
* 1) Initially you call the function using a cursor (v) value of 0.
* 2) The function performs one step of the iteration, and returns the
* new cursor value you must use in the next call.
* 3) When the returned cursor is 0, the iteration is complete.
*
* The function guarantees all elements present in the
* dictionary get returned between the start and end of the iteration.
* However it is possible some elements get returned multiple times.
*
* For every element returned, the callback argument 'fn' is
* called with 'privdata' as first argument and the dictionary entry
* 'de' as second argument.
*
* HOW IT WORKS.
*
* The iteration algorithm was designed by Pieter Noordhuis.
* The main idea is to increment a cursor starting from the higher order
* bits. That is, instead of incrementing the cursor normally, the bits
* of the cursor are reversed, then the cursor is incremented, and finally
* the bits are reversed again.
*
* This strategy is needed because the hash table may be resized between
* iteration calls.
*
* dict.c hash tables are always power of two in size, and they
* use chaining, so the position of an element in a given table is given
* by computing the bitwise AND between Hash(key) and SIZE-1
* (where SIZE-1 is always the mask that is equivalent to taking the rest
* of the division between the Hash of the key and SIZE).
*
* For example if the current hash table size is 16, the mask is
* (in binary) 1111. The position of a key in the hash table will always be
* the last four bits of the hash output, and so forth.
*
* WHAT HAPPENS IF THE TABLE CHANGES IN SIZE?
*
* If the hash table grows, elements can go anywhere in one multiple of
* the old bucket: for example let's say we already iterated with
* a 4 bit cursor 1100 (the mask is 1111 because hash table size = 16).
*
* If the hash table will be resized to 64 elements, then the new mask will
* be 111111. The new buckets you obtain by substituting in ??1100
* with either 0 or 1 can be targeted only by keys we already visited
* when scanning the bucket 1100 in the smaller hash table.
*
* By iterating the higher bits first, because of the inverted counter, the
* cursor does not need to restart if the table size gets bigger. It will
* continue iterating using cursors without '1100' at the end, and also
* without any other combination of the final 4 bits already explored.
*
* Similarly when the table size shrinks over time, for example going from
* 16 to 8, if a combination of the lower three bits (the mask for size 8
* is 111) were already completely explored, it would not be visited again
* because we are sure we tried, for example, both 0111 and 1111 (all the
* variations of the higher bit) so we don't need to test it again.
*
* WAIT... YOU HAVE *TWO* TABLES DURING REHASHING!
*
* Yes, this is true, but we always iterate the smaller table first, then
* we test all the expansions of the current cursor into the larger
* table. For example if the current cursor is 101 and we also have a
* larger table of size 16, we also test (0)101 and (1)101 inside the larger
* table. This reduces the problem back to having only one table, where
* the larger one, if it exists, is just an expansion of the smaller one.
*
* LIMITATIONS
*
* This iterator is completely stateless, and this is a huge advantage,
* including no additional memory used.
*
* The disadvantages resulting from this design are:
*
* 1) It is possible we return elements more than once. However this is usually
* easy to deal with in the application level.
* 2) The iterator must return multiple elements per call, as it needs to always
* return all the keys chained in a given bucket, and all the expansions, so
* we are sure we don't miss keys moving during rehashing.
* 3) The reverse cursor is somewhat hard to understand at first, but this
* comment is supposed to help.
*/
unsigned long dictScan(dict *d,
unsigned long v,
dictScanFunction *fn,
dictScanBucketFunction* bucketfn,
void *privdata)
{
int htidx0, htidx1;
const dictEntry *de, *next;
unsigned long m0, m1;
if (dictSize(d) == 0) return 0;
/* This is needed in case the scan callback tries to do dictFind or alike. */
dictPauseRehashing(d);
if (!dictIsRehashing(d)) {
htidx0 = 0;
m0 = DICTHT_SIZE_MASK(d->ht_size_exp[htidx0]);
/* Emit entries at cursor */
if (bucketfn) bucketfn(d, &d->ht_table[htidx0][v & m0]);
de = d->ht_table[htidx0][v & m0];
while (de) {
next = de->next;
fn(privdata, de);
de = next;
}
/* Set unmasked bits so incrementing the reversed cursor
* operates on the masked bits */
v |= ~m0;
/* Increment the reverse cursor */
v = rev(v);
v++;
v = rev(v);
} else {
htidx0 = 0;
htidx1 = 1;
/* Make sure t0 is the smaller and t1 is the bigger table */
if (DICTHT_SIZE(d->ht_size_exp[htidx0]) > DICTHT_SIZE(d->ht_size_exp[htidx1])) {
htidx0 = 1;
htidx1 = 0;
}
m0 = DICTHT_SIZE_MASK(d->ht_size_exp[htidx0]);
m1 = DICTHT_SIZE_MASK(d->ht_size_exp[htidx1]);
/* Emit entries at cursor */
if (bucketfn) bucketfn(d, &d->ht_table[htidx0][v & m0]);
de = d->ht_table[htidx0][v & m0];
while (de) {
next = de->next;
fn(privdata, de);
de = next;
}
/* Iterate over indices in larger table that are the expansion
* of the index pointed to by the cursor in the smaller table */
do {
/* Emit entries at cursor */
if (bucketfn) bucketfn(d, &d->ht_table[htidx1][v & m1]);
de = d->ht_table[htidx1][v & m1];
while (de) {
next = de->next;
fn(privdata, de);
de = next;
}
/* Increment the reverse cursor not covered by the smaller mask.*/
v |= ~m1;
v = rev(v);
v++;
v = rev(v);
/* Continue while bits covered by mask difference is non-zero */
} while (v & (m0 ^ m1));
}
dictResumeRehashing(d);
return v;
}
/* ------------------------- private functions ------------------------------ */
/* Because we may need to allocate huge memory chunk at once when dict
* expands, we will check this allocation is allowed or not if the dict
* type has expandAllowed member function. */
static int dictTypeExpandAllowed(dict *d) {
if (d->type->expandAllowed == NULL) return 1;
return d->type->expandAllowed(
DICTHT_SIZE(_dictNextExp(d->ht_used[0] + 1)) * sizeof(dictEntry*),
(double)d->ht_used[0] / DICTHT_SIZE(d->ht_size_exp[0]));
}
/* Expand the hash table if needed */
static int _dictExpandIfNeeded(dict *d)
{
/* Incremental rehashing already in progress. Return. */
if (dictIsRehashing(d)) return DICT_OK;
/* If the hash table is empty expand it to the initial size. */
if (DICTHT_SIZE(d->ht_size_exp[0]) == 0) return dictExpand(d, DICT_HT_INITIAL_SIZE);
/* If we reached the 1:1 ratio, and we are allowed to resize the hash
* table (global setting) or we should avoid it but the ratio between
* elements/buckets is over the "safe" threshold, we resize doubling
* the number of buckets. */
if (d->ht_used[0] >= DICTHT_SIZE(d->ht_size_exp[0]) &&
(dict_can_resize ||
d->ht_used[0]/ DICTHT_SIZE(d->ht_size_exp[0]) > dict_force_resize_ratio) &&
dictTypeExpandAllowed(d))
{
return dictExpand(d, d->ht_used[0] + 1);
}
return DICT_OK;
}
/* TODO: clz optimization */
/* Our hash table capability is a power of two */
static signed char _dictNextExp(unsigned long size)
{
unsigned char e = DICT_HT_INITIAL_EXP;
if (size >= LONG_MAX) return (8*sizeof(long)-1);
while(1) {
if (((unsigned long)1<<e) >= size)
return e;
e++;
}
}
/* Returns the index of a free slot that can be populated with
* a hash entry for the given 'key'.
* If the key already exists, -1 is returned
* and the optional output parameter may be filled.
*
* Note that if we are in the process of rehashing the hash table, the
* index is always returned in the context of the second (new) hash table. */
static long _dictKeyIndex(dict *d, const void *key, uint64_t hash, dictEntry **existing)
{
unsigned long idx, table;
dictEntry *he;
if (existing) *existing = NULL;
/* Expand the hash table if needed */
if (_dictExpandIfNeeded(d) == DICT_ERR)
return -1;
for (table = 0; table <= 1; table++) {
idx = hash & DICTHT_SIZE_MASK(d->ht_size_exp[table]);
/* Search if this slot does not already contain the given key */
he = d->ht_table[table][idx];
while(he) {
if (key==he->key || dictCompareKeys(d, key, he->key)) {
if (existing) *existing = he;
return -1;
}
he = he->next;
}
if (!dictIsRehashing(d)) break;
}
return idx;
}
void dictEmpty(dict *d, void(callback)(dict*)) {
_dictClear(d,0,callback);
_dictClear(d,1,callback);
d->rehashidx = -1;
d->pauserehash = 0;
}
void dictEnableResize(void) {
dict_can_resize = 1;
}
void dictDisableResize(void) {
dict_can_resize = 0;
}
uint64_t dictGetHash(dict *d, const void *key) {
return dictHashKey(d, key);
}
/* Finds the dictEntry reference by using pointer and pre-calculated hash.
* oldkey is a dead pointer and should not be accessed.
* the hash value should be provided using dictGetHash.
* no string / key comparison is performed.
* return value is the reference to the dictEntry if found, or NULL if not found. */
dictEntry **dictFindEntryRefByPtrAndHash(dict *d, const void *oldptr, uint64_t hash) {
dictEntry *he, **heref;
unsigned long idx, table;
if (dictSize(d) == 0) return NULL; /* dict is empty */
for (table = 0; table <= 1; table++) {
idx = hash & DICTHT_SIZE_MASK(d->ht_size_exp[table]);
heref = &d->ht_table[table][idx];
he = *heref;
while(he) {
if (oldptr==he->key)
return heref;
heref = &he->next;
he = *heref;
}
if (!dictIsRehashing(d)) return NULL;
}
return NULL;
}
/* ------------------------------- Debugging ---------------------------------*/
#define DICT_STATS_VECTLEN 50
size_t _dictGetStatsHt(char *buf, size_t bufsize, dict *d, int htidx) {
unsigned long i, slots = 0, chainlen, maxchainlen = 0;
unsigned long totchainlen = 0;
unsigned long clvector[DICT_STATS_VECTLEN];
size_t l = 0;
if (d->ht_used[htidx] == 0) {
return snprintf(buf,bufsize,
"No stats available for empty dictionaries\n");
}
/* Compute stats. */
for (i = 0; i < DICT_STATS_VECTLEN; i++) clvector[i] = 0;
for (i = 0; i < DICTHT_SIZE(d->ht_size_exp[htidx]); i++) {
dictEntry *he;
if (d->ht_table[htidx][i] == NULL) {
clvector[0]++;
continue;
}
slots++;
/* For each hash entry on this slot... */
chainlen = 0;
he = d->ht_table[htidx][i];
while(he) {
chainlen++;
he = he->next;
}
clvector[(chainlen < DICT_STATS_VECTLEN) ? chainlen : (DICT_STATS_VECTLEN-1)]++;
if (chainlen > maxchainlen) maxchainlen = chainlen;
totchainlen += chainlen;
}
/* Generate human readable stats. */
l += snprintf(buf+l,bufsize-l,
"Hash table %d stats (%s):\n"
" table size: %lu\n"
" number of elements: %lu\n"
" different slots: %lu\n"
" max chain length: %lu\n"
" avg chain length (counted): %.02f\n"
" avg chain length (computed): %.02f\n"
" Chain length distribution:\n",
htidx, (htidx == 0) ? "main hash table" : "rehashing target",
DICTHT_SIZE(d->ht_size_exp[htidx]), d->ht_used[htidx], slots, maxchainlen,
(float)totchainlen/slots, (float)d->ht_used[htidx]/slots);
for (i = 0; i < DICT_STATS_VECTLEN-1; i++) {
if (clvector[i] == 0) continue;
if (l >= bufsize) break;
l += snprintf(buf+l,bufsize-l,
" %s%ld: %ld (%.02f%%)\n",
(i == DICT_STATS_VECTLEN-1)?">= ":"",
i, clvector[i], ((float)clvector[i]/DICTHT_SIZE(d->ht_size_exp[htidx]))*100);
}
/* Unlike snprintf(), return the number of characters actually written. */
if (bufsize) buf[bufsize-1] = '\0';
return strlen(buf);
}
void dictGetStats(char *buf, size_t bufsize, dict *d) {
size_t l;
char *orig_buf = buf;
size_t orig_bufsize = bufsize;
l = _dictGetStatsHt(buf,bufsize,d,0);
buf += l;
bufsize -= l;
if (dictIsRehashing(d) && bufsize > 0) {
_dictGetStatsHt(buf,bufsize,d,1);
}
/* Make sure there is a NULL term at the end. */
if (orig_bufsize) orig_buf[orig_bufsize-1] = '\0';
}
/* ------------------------------- Benchmark ---------------------------------*/
#ifdef REDIS_TEST
#define UNUSED(V) ((void) V)
uint64_t hashCallback(const void *key) {
return dictGenHashFunction((unsigned char*)key, strlen((char*)key));
}
int compareCallback(dict *d, const void *key1, const void *key2) {
int l1,l2;
UNUSED(d);
l1 = strlen((char*)key1);
l2 = strlen((char*)key2);
if (l1 != l2) return 0;
return memcmp(key1, key2, l1) == 0;
}
void freeCallback(dict *d, void *val) {
UNUSED(d);
zfree(val);
}
char *stringFromLongLong(long long value) {
char buf[32];
int len;
char *s;
len = sprintf(buf,"%lld",value);
s = zmalloc(len+1);
memcpy(s, buf, len);
s[len] = '\0';
return s;
}
dictType BenchmarkDictType = {
hashCallback,
NULL,
NULL,
compareCallback,
freeCallback,
NULL,
NULL
};
#define start_benchmark() start = timeInMilliseconds()
#define end_benchmark(msg) do { \
elapsed = timeInMilliseconds()-start; \
printf(msg ": %ld items in %lld ms\n", count, elapsed); \
} while(0)
/* ./redis-server test dict [<count> | --accurate] */
int dictTest(int argc, char **argv, int accurate) {
long j;
long long start, elapsed;
dict *dict = dictCreate(&BenchmarkDictType);
long count = 0;
if (argc == 4) {
if (accurate) {
count = 5000000;
} else {
count = strtol(argv[3],NULL,10);
}
} else {
count = 5000;
}
start_benchmark();
for (j = 0; j < count; j++) {
int retval = dictAdd(dict,stringFromLongLong(j),(void*)j);
assert(retval == DICT_OK);
}
end_benchmark("Inserting");
assert((long)dictSize(dict) == count);
/* Wait for rehashing. */
while (dictIsRehashing(dict)) {
dictRehashMilliseconds(dict,100);
}
start_benchmark();
for (j = 0; j < count; j++) {
char *key = stringFromLongLong(j);
dictEntry *de = dictFind(dict,key);
assert(de != NULL);
zfree(key);
}
end_benchmark("Linear access of existing elements");
start_benchmark();
for (j = 0; j < count; j++) {
char *key = stringFromLongLong(j);
dictEntry *de = dictFind(dict,key);
assert(de != NULL);
zfree(key);
}
end_benchmark("Linear access of existing elements (2nd round)");
start_benchmark();
for (j = 0; j < count; j++) {
char *key = stringFromLongLong(rand() % count);
dictEntry *de = dictFind(dict,key);
assert(de != NULL);
zfree(key);
}
end_benchmark("Random access of existing elements");
start_benchmark();
for (j = 0; j < count; j++) {
dictEntry *de = dictGetRandomKey(dict);
assert(de != NULL);
}
end_benchmark("Accessing random keys");
start_benchmark();
for (j = 0; j < count; j++) {
char *key = stringFromLongLong(rand() % count);
key[0] = 'X';
dictEntry *de = dictFind(dict,key);
assert(de == NULL);
zfree(key);
}
end_benchmark("Accessing missing");
start_benchmark();
for (j = 0; j < count; j++) {
char *key = stringFromLongLong(j);
int retval = dictDelete(dict,key);
assert(retval == DICT_OK);
key[0] += 17; /* Change first number to letter. */
retval = dictAdd(dict,key,(void*)j);
assert(retval == DICT_OK);
}
end_benchmark("Removing and adding");
dictRelease(dict);
return 0;
}
#endif
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