From 307c34b028d353154aa268eceb38e0331c8275cf Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= Date: Thu, 22 Oct 2020 15:43:26 +0200 Subject: [PATCH] Hashtable: use dynamic growth and use primes as size Dynamically increase the hashmap size to not exceed the load factor and avoid too long chains. Switch from Separate Chaining to Robin Hood linear probing to improve cache locality. Use primes as size to further avoid collisions. E.g. on a standard kde system the number of entries in the ProcessTable might be around 650. --- Hashtable.c | 276 ++++++++++++++++++++++++++++++++++++++------------- Hashtable.h | 6 +- UsersTable.c | 2 +- 3 files changed, 210 insertions(+), 74 deletions(-) diff --git a/Hashtable.c b/Hashtable.c index 606dfd60..cdfb4ec3 100644 --- a/Hashtable.c +++ b/Hashtable.c @@ -8,32 +8,55 @@ in the source distribution for its full text. #include "Hashtable.h" #include "XUtils.h" -#include #include +#include +#include #ifndef NDEBUG +static void Hashtable_dump(const Hashtable* this) { + fprintf(stderr, "Hashtable %p: size=%u items=%u owner=%s\n", + (const void*)this, + this->size, + this->items, + this->owner ? "yes" : "no"); + + unsigned int items = 0; + for (unsigned int i = 0; i < this->size; i++) { + fprintf(stderr, " item %5u: key = %5u probe = %2u value = %p\n", + i, + this->buckets[i].key, + this->buckets[i].probe, + this->buckets[i].value ? (const void*)this->buckets[i].value : "(nil)"); + + if (this->buckets[i].value) + items++; + } + + fprintf(stderr, "Hashtable %p: items=%u counted=%u\n", + (const void*)this, + this->items, + items); +} + static bool Hashtable_isConsistent(const Hashtable* this) { unsigned int items = 0; for (unsigned int i = 0; i < this->size; i++) { - HashtableItem* bucket = this->buckets[i]; - while (bucket) { + if (this->buckets[i].value) items++; - bucket = bucket->next; - } } - return items == this->items; + bool res = items == this->items; + if (!res) + Hashtable_dump(this); + return res; } unsigned int Hashtable_count(const Hashtable* this) { unsigned int items = 0; for (unsigned int i = 0; i < this->size; i++) { - HashtableItem* bucket = this->buckets[i]; - while (bucket) { + if (this->buckets[i].value) items++; - bucket = bucket->next; - } } assert(items == this->items); return items; @@ -41,14 +64,25 @@ unsigned int Hashtable_count(const Hashtable* this) { #endif /* NDEBUG */ -static HashtableItem* HashtableItem_new(hkey_t key, void* value) { - HashtableItem* this; +/* https://oeis.org/A014234 */ +static const uint64_t OEISprimes[] = { + 2, 3, 7, 13, 31, 61, 127, 251, 509, 1021, 2039, 4093, 8191, + 16381, 32749, 65521, 131071, 262139, 524287, 1048573, + 2097143, 4194301, 8388593, 16777213, 33554393, + 67108859, 134217689, 268435399, 536870909, 1073741789, + 2147483647, 4294967291, 8589934583, 17179869143, + 34359738337, 68719476731, 137438953447 +}; - this = xMalloc(sizeof(HashtableItem)); - this->key = key; - this->value = value; - this->next = NULL; - return this; +static uint64_t nextPrime(unsigned int n) { + assert(n <= OEISprimes[ARRAYSIZE(OEISprimes) - 1]); + + for (unsigned int i = 0; i < ARRAYSIZE(OEISprimes); i++) { + if (n <= OEISprimes[i]) + return OEISprimes[i]; + } + + return OEISprimes[ARRAYSIZE(OEISprimes) - 1]; } Hashtable* Hashtable_new(unsigned int size, bool owner) { @@ -56,102 +90,202 @@ Hashtable* Hashtable_new(unsigned int size, bool owner) { this = xMalloc(sizeof(Hashtable)); this->items = 0; - this->size = size; - this->buckets = (HashtableItem**) xCalloc(size, sizeof(HashtableItem*)); + this->size = size ? nextPrime(size) : 13; + this->buckets = (HashtableItem*) xCalloc(this->size, sizeof(HashtableItem)); this->owner = owner; assert(Hashtable_isConsistent(this)); return this; } void Hashtable_delete(Hashtable* this) { - assert(Hashtable_isConsistent(this)); - for (unsigned int i = 0; i < this->size; i++) { - HashtableItem* walk = this->buckets[i]; - while (walk != NULL) { - if (this->owner) - free(walk->value); - HashtableItem* savedWalk = walk; - walk = savedWalk->next; - free(savedWalk); - } + assert(Hashtable_isConsistent(this)); + + if (this->owner) { + for (unsigned int i = 0; i < this->size; i++) + free(this->buckets[i].value); } + free(this->buckets); free(this); } -void Hashtable_put(Hashtable* this, hkey_t key, void* value) { +static void insert(Hashtable* this, hkey_t key, void* value) { unsigned int index = key % this->size; - HashtableItem** bucketPtr = &(this->buckets[index]); - while (true) - if (*bucketPtr == NULL) { - *bucketPtr = HashtableItem_new(key, value); - this->items++; - break; - } else if ((*bucketPtr)->key == key) { - if (this->owner && (*bucketPtr)->value != value) - free((*bucketPtr)->value); + unsigned int probe = 0; +#ifndef NDEBUG + unsigned int origIndex = index; +#endif - (*bucketPtr)->value = value; - break; - } else { - bucketPtr = &((*bucketPtr)->next); + for (;;) { + if (!this->buckets[index].value) { + this->items++; + this->buckets[index].key = key; + this->buckets[index].probe = probe; + this->buckets[index].value = value; + return; } + if (this->buckets[index].key == key) { + if (this->owner && this->buckets[index].value != value) + free(this->buckets[index].value); + this->buckets[index].value = value; + return; + } + + /* Robin Hood swap */ + if (probe > this->buckets[index].probe) { + HashtableItem tmp = this->buckets[index]; + + this->buckets[index].key = key; + this->buckets[index].probe = probe; + this->buckets[index].value = value; + + key = tmp.key; + probe = tmp.probe; + value = tmp.value; + } + + index = (index + 1) % this->size; + probe++; + + assert(index != origIndex); + } +} + +void Hashtable_setSize(Hashtable* this, unsigned int size) { + assert(Hashtable_isConsistent(this)); + + if (size <= this->items) + return; + + HashtableItem* oldBuckets = this->buckets; + unsigned int oldSize = this->size; + + this->size = nextPrime(size); + this->buckets = (HashtableItem*) xCalloc(this->size, sizeof(HashtableItem)); + this->items = 0; + + /* rehash */ + for (unsigned int i = 0; i < oldSize; i++) { + if (!oldBuckets[i].value) + continue; + + insert(this, oldBuckets[i].key, oldBuckets[i].value); + } + + free(oldBuckets); + + assert(Hashtable_isConsistent(this)); +} + +void Hashtable_put(Hashtable* this, hkey_t key, void* value) { + + assert(Hashtable_isConsistent(this)); + assert(this->size > 0); + assert(value); + + /* grow on load-factor > 0.7 */ + if (10 * this->items > 7 * this->size) + Hashtable_setSize(this, 2 * this->size); + + insert(this, key, value); + + assert(Hashtable_isConsistent(this)); + assert(Hashtable_get(this, key) != NULL); + assert(this->size > this->items); } void* Hashtable_remove(Hashtable* this, hkey_t key) { unsigned int index = key % this->size; + unsigned int probe = 0; +#ifndef NDEBUG + unsigned int origIndex = index; +#endif assert(Hashtable_isConsistent(this)); - HashtableItem** bucket; - for (bucket = &(this->buckets[index]); *bucket; bucket = &((*bucket)->next) ) { - if ((*bucket)->key == key) { - void* value = (*bucket)->value; - HashtableItem* next = (*bucket)->next; - free(*bucket); - (*bucket) = next; - this->items--; + void* res = NULL; + + while (this->buckets[index].value) { + if (this->buckets[index].key == key) { if (this->owner) { - free(value); - assert(Hashtable_isConsistent(this)); - return NULL; + free(this->buckets[index].value); } else { - assert(Hashtable_isConsistent(this)); - return value; + res = this->buckets[index].value; } + + unsigned int next = (index + 1) % this->size; + + while (this->buckets[next].value && this->buckets[next].probe > 0) { + this->buckets[index] = this->buckets[next]; + this->buckets[index].probe -= 1; + + index = next; + next = (index + 1) % this->size; + } + + /* set empty after backward shifting */ + this->buckets[index].value = NULL; + this->items--; + + break; } + + if (this->buckets[index].probe < probe) + break; + + index = (index + 1) % this->size; + probe++; + + assert(index != origIndex); } + assert(Hashtable_isConsistent(this)); - return NULL; + assert(Hashtable_get(this, key) == NULL); + + /* shrink on load-factor < 0.125 */ + if (8 * this->items < this->size) + Hashtable_setSize(this, this->size / 2); + + return res; } void* Hashtable_get(Hashtable* this, hkey_t key) { unsigned int index = key % this->size; - HashtableItem* bucketPtr = this->buckets[index]; - while (true) { - if (bucketPtr == NULL) { - assert(Hashtable_isConsistent(this)); - return NULL; - } else if (bucketPtr->key == key) { - assert(Hashtable_isConsistent(this)); - return bucketPtr->value; - } else { - bucketPtr = bucketPtr->next; + unsigned int probe = 0; + void* res = NULL; +#ifndef NDEBUG + unsigned int origIndex = index; +#endif + + assert(Hashtable_isConsistent(this)); + + while (this->buckets[index].value) { + if (this->buckets[index].key == key) { + res = this->buckets[index].value; + break; } + + if (this->buckets[index].probe < probe) + break; + + index = (index + 1) != this->size ? (index + 1) : 0; + probe++; + + assert(index != origIndex); } + + return res; } void Hashtable_foreach(Hashtable* this, Hashtable_PairFunction f, void* userData) { assert(Hashtable_isConsistent(this)); for (unsigned int i = 0; i < this->size; i++) { - HashtableItem* walk = this->buckets[i]; - while (walk != NULL) { + HashtableItem* walk = &this->buckets[i]; + if (walk->value) f(walk->key, walk->value, userData); - walk = walk->next; - } } assert(Hashtable_isConsistent(this)); } diff --git a/Hashtable.h b/Hashtable.h index 15af9e0d..f7d1aae2 100644 --- a/Hashtable.h +++ b/Hashtable.h @@ -16,13 +16,13 @@ typedef void(*Hashtable_PairFunction)(hkey_t key, void* value, void* userdata); typedef struct HashtableItem_ { hkey_t key; + unsigned int probe; void* value; - struct HashtableItem_* next; } HashtableItem; typedef struct Hashtable_ { unsigned int size; - HashtableItem** buckets; + HashtableItem* buckets; unsigned int items; bool owner; } Hashtable; @@ -37,6 +37,8 @@ Hashtable* Hashtable_new(unsigned int size, bool owner); void Hashtable_delete(Hashtable* this); +void Hashtable_setSize(Hashtable* this, unsigned int size); + void Hashtable_put(Hashtable* this, hkey_t key, void* value); void* Hashtable_remove(Hashtable* this, hkey_t key); diff --git a/UsersTable.c b/UsersTable.c index 25e44883..fdbfd68f 100644 --- a/UsersTable.c +++ b/UsersTable.c @@ -20,7 +20,7 @@ in the source distribution for its full text. UsersTable* UsersTable_new() { UsersTable* this; this = xMalloc(sizeof(UsersTable)); - this->users = Hashtable_new(20, true); + this->users = Hashtable_new(10, true); return this; }