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Simplifications to the symbol table implementation in hash.c. For very small

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symbol tables (less than 10 entries) a simple linked list is used instead
of a hash table.  Number of hash table buckets is limited to prevent large
allocations. (CVS 6559)

FossilOrigin-Name: 5c737835dec9e6038b304c198aa14337a6f23c1c
This commit is contained in:
drh
2009-04-28 15:43:45 +00:00
parent ebb329397c
commit 8a1e594c9f
6 changed files with 124 additions and 109 deletions
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171
src/hash.c
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@@ -12,7 +12,7 @@
** This is the implementation of generic hash-tables
** used in SQLite.
**
** $Id: hash.c,v 1.34 2009/04/28 13:01:09 drh Exp $
** $Id: hash.c,v 1.35 2009/04/28 15:43:45 drh Exp $
*/
#include "sqliteInt.h"
#include <assert.h>
@@ -60,7 +60,7 @@ void sqlite3HashClear(Hash *pH){
/*
** Hash and comparison functions when the mode is SQLITE_HASH_STRING
*/
static int strHash(const void *pKey, int nKey){
static unsigned int strHash(const void *pKey, int nKey){
const char *z = (const char *)pKey;
int h = 0;
assert( nKey>0 );
@@ -68,7 +68,7 @@ static int strHash(const void *pKey, int nKey){
h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];
nKey--;
}
return h & 0x7fffffff;
return h;
}
static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
if( n1!=n2 ) return 1;
@@ -76,7 +76,8 @@ static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
}
/* Link an element into the hash table
/* Link pNew element into the hash table pH. If pEntry!=0 then also
** insert pNew into the pEntry hash bucket.
*/
static void insertElement(
Hash *pH, /* The complete hash table */
@@ -84,7 +85,13 @@ static void insertElement(
HashElem *pNew /* The element to be inserted */
){
HashElem *pHead; /* First element already in pEntry */
pHead = pEntry->chain;
if( pEntry ){
pHead = pEntry->count ? pEntry->chain : 0;
pEntry->count++;
pEntry->chain = pNew;
}else{
pHead = 0;
}
if( pHead ){
pNew->next = pHead;
pNew->prev = pHead->prev;
@@ -97,44 +104,45 @@ static void insertElement(
pNew->prev = 0;
pH->first = pNew;
}
pEntry->count++;
pEntry->chain = pNew;
}
/* Resize the hash table so that it cantains "new_size" buckets.
** "new_size" must be a power of 2. The hash table might fail
** to resize if sqlite3_malloc() fails.
**
** The hash table might fail to resize if sqlite3_malloc() fails or
** if the new size is the same as the prior size.
** Return TRUE if the resize occurs and false if not.
*/
static void rehash(Hash *pH, int new_size){
static int rehash(Hash *pH, unsigned int new_size){
struct _ht *new_ht; /* The new hash table */
HashElem *elem, *next_elem; /* For looping over existing elements */
#ifdef SQLITE_MALLOC_SOFT_LIMIT
#if SQLITE_MALLOC_SOFT_LIMIT>0
if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){
new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);
}
if( new_size==pH->htsize ) return;
if( new_size==pH->htsize ) return 0;
#endif
/* There is a call to sqlite3_malloc() inside rehash(). If there is
** already an allocation at pH->ht, then if this malloc() fails it
** is benign (since failing to resize a hash table is a performance
** hit only, not a fatal error).
/* The inability to allocates space for a larger hash table is
** a performance hit but it is not a fatal error. So mark the
** allocation as a benign.
*/
if( pH->htsize>0 ) sqlite3BeginBenignMalloc();
new_ht = (struct _ht *)sqlite3MallocZero( new_size*sizeof(struct _ht) );
if( pH->htsize>0 ) sqlite3EndBenignMalloc();
sqlite3BeginBenignMalloc();
new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
sqlite3EndBenignMalloc();
if( new_ht==0 ) return;
if( new_ht==0 ) return 0;
sqlite3_free(pH->ht);
pH->ht = new_ht;
pH->htsize = new_size;
pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht);
memset(new_ht, 0, new_size*sizeof(struct _ht));
for(elem=pH->first, pH->first=0; elem; elem = next_elem){
int h = strHash(elem->pKey, elem->nKey) & (new_size-1);
unsigned int h = strHash(elem->pKey, elem->nKey) % new_size;
next_elem = elem->next;
insertElement(pH, &new_ht[h], elem);
}
return 1;
}
/* This function (for internal use only) locates an element in an
@@ -144,8 +152,8 @@ static void rehash(Hash *pH, int new_size){
static HashElem *findElementGivenHash(
const Hash *pH, /* The pH to be searched */
const void *pKey, /* The key we are searching for */
int nKey,
int h /* The hash for this key. */
int nKey, /* Bytes in key (not counting zero terminator) */
unsigned int h /* The hash for this key. */
){
HashElem *elem; /* Used to loop thru the element list */
int count; /* Number of elements left to test */
@@ -154,12 +162,15 @@ static HashElem *findElementGivenHash(
struct _ht *pEntry = &pH->ht[h];
elem = pEntry->chain;
count = pEntry->count;
while( count-- && elem ){
if( strCompare(elem->pKey,elem->nKey,pKey,nKey)==0 ){
return elem;
}
elem = elem->next;
}else{
elem = pH->first;
count = pH->count;
}
while( count-- && ALWAYS(elem) ){
if( strCompare(elem->pKey,elem->nKey,pKey,nKey)==0 ){
return elem;
}
elem = elem->next;
}
return 0;
}
@@ -170,7 +181,7 @@ static HashElem *findElementGivenHash(
static void removeElementGivenHash(
Hash *pH, /* The pH containing "elem" */
HashElem* elem, /* The element to be removed from the pH */
int h /* Hash value for the element */
unsigned int h /* Hash value for the element */
){
struct _ht *pEntry;
if( elem->prev ){
@@ -181,13 +192,13 @@ static void removeElementGivenHash(
if( elem->next ){
elem->next->prev = elem->prev;
}
pEntry = &pH->ht[h];
if( pEntry->chain==elem ){
pEntry->chain = elem->next;
}
pEntry->count--;
if( pEntry->count<=0 ){
pEntry->chain = 0;
if( pH->ht ){
pEntry = &pH->ht[h];
if( pEntry->chain==elem ){
pEntry->chain = elem->next;
}
pEntry->count--;
assert( pEntry->count>=0 );
}
if( pH->copyKey ){
sqlite3_free(elem->pKey);
@@ -201,28 +212,23 @@ static void removeElementGivenHash(
}
}
/* Attempt to locate an element of the hash table pH with a key
** that matches pKey,nKey. Return a pointer to the corresponding
** HashElem structure for this element if it is found, or NULL
** otherwise.
*/
HashElem *sqlite3HashFindElem(const Hash *pH, const void *pKey, int nKey){
int h; /* A hash on key */
HashElem *elem; /* The element that matches key */
if( pH==0 || pH->ht==0 ) return 0;
h = strHash(pKey,nKey);
elem = findElementGivenHash(pH,pKey,nKey, h % pH->htsize);
return elem;
}
/* Attempt to locate an element of the hash table pH with a key
** that matches pKey,nKey. Return the data for this element if it is
** found, or NULL if there is no match.
*/
void *sqlite3HashFind(const Hash *pH, const void *pKey, int nKey){
HashElem *elem; /* The element that matches key */
elem = sqlite3HashFindElem(pH, pKey, nKey);
unsigned int h; /* A hash on key */
assert( pH!=0 );
assert( pKey!=0 );
assert( nKey>0 );
if( pH->ht ){
h = strHash(pKey, nKey) % pH->htsize;
}else{
h = 0;
}
elem = findElementGivenHash(pH, pKey, nKey, h);
return elem ? elem->data : 0;
}
@@ -242,34 +248,36 @@ void *sqlite3HashFind(const Hash *pH, const void *pKey, int nKey){
** element corresponding to "key" is removed from the hash table.
*/
void *sqlite3HashInsert(Hash *pH, const void *pKey, int nKey, void *data){
int hraw; /* Raw hash value of the key */
int h; /* the hash of the key modulo hash table size */
unsigned int h; /* the hash of the key modulo hash table size */
HashElem *elem; /* Used to loop thru the element list */
HashElem *new_elem; /* New element added to the pH */
assert( pH!=0 );
hraw = strHash(pKey, nKey);
assert( pKey!=0 );
assert( nKey>0 );
if( pH->htsize ){
h = hraw % pH->htsize;
elem = findElementGivenHash(pH,pKey,nKey,h);
if( elem ){
void *old_data = elem->data;
if( data==0 ){
removeElementGivenHash(pH,elem,h);
}else{
elem->data = data;
if( !pH->copyKey ){
elem->pKey = (void *)pKey;
}
assert(nKey==elem->nKey);
h = strHash(pKey, nKey) % pH->htsize;
}else{
h = 0;
}
elem = findElementGivenHash(pH,pKey,nKey,h);
if( elem ){
void *old_data = elem->data;
if( data==0 ){
removeElementGivenHash(pH,elem,h);
}else{
elem->data = data;
if( !pH->copyKey ){
elem->pKey = (void *)pKey;
}
return old_data;
assert(nKey==elem->nKey);
}
return old_data;
}
if( data==0 ) return 0;
new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );
if( new_elem==0 ) return data;
if( pH->copyKey && pKey!=0 ){
if( pH->copyKey ){
new_elem->pKey = sqlite3Malloc( nKey );
if( new_elem->pKey==0 ){
sqlite3_free(new_elem);
@@ -280,24 +288,17 @@ void *sqlite3HashInsert(Hash *pH, const void *pKey, int nKey, void *data){
new_elem->pKey = (void*)pKey;
}
new_elem->nKey = nKey;
new_elem->data = data;
pH->count++;
if( pH->htsize==0 ){
rehash(pH, 128/sizeof(pH->ht[0]));
if( pH->htsize==0 ){
pH->count = 0;
if( pH->copyKey ){
sqlite3_free(new_elem->pKey);
}
sqlite3_free(new_elem);
return data;
if( pH->count>=10 && pH->count > 2*pH->htsize ){
if( rehash(pH, pH->count*2) && pH->htsize ){
h = strHash(pKey, nKey) % pH->htsize;
}
}
if( pH->count > pH->htsize ){
rehash(pH,pH->htsize*2);
if( pH->ht ){
insertElement(pH, &pH->ht[h], new_elem);
}else{
insertElement(pH, 0, new_elem);
}
assert( pH->htsize>0 );
h = hraw % pH->htsize;
insertElement(pH, &pH->ht[h], new_elem);
new_elem->data = data;
return 0;
}