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authorhongbotian <hongbo.tianhongbo@huawei.com>2015-11-30 01:45:08 -0500
committerhongbotian <hongbo.tianhongbo@huawei.com>2015-11-30 01:45:08 -0500
commite8ec7aa8e38a93f5b034ac74cebce5de23710317 (patch)
treeaa031937bf856c1f8d6ad7877b8d2cb0224da5ef /rubbos/app/httpd-2.0.64/modules/experimental/cache_hash.c
parentcc40af334e619bb549038238507407866f774f8f (diff)
upload http
JIRA: BOTTLENECK-10 Change-Id: I7598427ff904df438ce77c2819ee48ac75ffa8da Signed-off-by: hongbotian <hongbo.tianhongbo@huawei.com>
Diffstat (limited to 'rubbos/app/httpd-2.0.64/modules/experimental/cache_hash.c')
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+/* Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "apr_general.h"
+
+#include "mod_cache.h"
+#include "cache_hash.h"
+
+#if APR_HAVE_STDLIB_H
+#include <stdlib.h>
+#endif
+#if APR_HAVE_STRING_H
+#include <string.h>
+#endif
+
+
+/*
+ * The internal form of a hash table.
+ *
+ * The table is an array indexed by the hash of the key; collisions
+ * are resolved by hanging a linked list of hash entries off each
+ * element of the array. Although this is a really simple design it
+ * isn't too bad given that pools have a low allocation overhead.
+ */
+
+typedef struct cache_hash_entry_t cache_hash_entry_t;
+
+struct cache_hash_entry_t {
+ cache_hash_entry_t *next;
+ unsigned int hash;
+ const void *key;
+ apr_ssize_t klen;
+ const void *val;
+};
+
+/*
+ * Data structure for iterating through a hash table.
+ *
+ * We keep a pointer to the next hash entry here to allow the current
+ * hash entry to be freed or otherwise mangled between calls to
+ * cache_hash_next().
+ */
+struct cache_hash_index_t {
+ cache_hash_t *ht;
+ cache_hash_entry_t *this, *next;
+ int index;
+};
+
+/*
+ * The size of the array is always a power of two. We use the maximum
+ * index rather than the size so that we can use bitwise-AND for
+ * modular arithmetic.
+ * The count of hash entries may be greater depending on the chosen
+ * collision rate.
+ */
+struct cache_hash_t {
+ cache_hash_entry_t **array;
+ cache_hash_index_t iterator; /* For cache_hash_first(NULL, ...) */
+ int count, max;
+};
+
+/*
+ * Hash creation functions.
+ */
+static cache_hash_entry_t **alloc_array(cache_hash_t *ht, int max)
+{
+ return calloc(1, sizeof(*ht->array) * (max + 1));
+}
+
+CACHE_DECLARE(cache_hash_t *) cache_hash_make(apr_size_t size)
+{
+ cache_hash_t *ht;
+ ht = malloc(sizeof(cache_hash_t));
+ if (!ht) {
+ return NULL;
+ }
+ ht->count = 0;
+ ht->max = size;
+ ht->array = alloc_array(ht, ht->max);
+ if (!ht->array) {
+ free(ht);
+ return NULL;
+ }
+ return ht;
+}
+
+CACHE_DECLARE(void) cache_hash_free(cache_hash_t *ht)
+{
+ if (ht) {
+ if (ht->array) {
+ free (ht->array);
+ }
+ free (ht);
+ }
+}
+/*
+ * Hash iteration functions.
+ */
+
+CACHE_DECLARE(cache_hash_index_t *) cache_hash_next(cache_hash_index_t *hi)
+{
+ hi->this = hi->next;
+ while (!hi->this) {
+ if (hi->index > hi->ht->max)
+ return NULL;
+ hi->this = hi->ht->array[hi->index++];
+ }
+ hi->next = hi->this->next;
+ return hi;
+}
+
+CACHE_DECLARE(cache_hash_index_t *) cache_hash_first(cache_hash_t *ht)
+{
+ cache_hash_index_t *hi;
+
+ hi = &ht->iterator;
+ hi->ht = ht;
+ hi->index = 0;
+ hi->this = NULL;
+ hi->next = NULL;
+ return cache_hash_next(hi);
+}
+
+CACHE_DECLARE(void) cache_hash_this(cache_hash_index_t *hi,
+ const void **key,
+ apr_ssize_t *klen,
+ void **val)
+{
+ if (key) *key = hi->this->key;
+ if (klen) *klen = hi->this->klen;
+ if (val) *val = (void *)hi->this->val;
+}
+
+
+/*
+ * This is where we keep the details of the hash function and control
+ * the maximum collision rate.
+ *
+ * If val is non-NULL it creates and initializes a new hash entry if
+ * there isn't already one there; it returns an updatable pointer so
+ * that hash entries can be removed.
+ */
+
+static cache_hash_entry_t **find_entry(cache_hash_t *ht,
+ const void *key,
+ apr_ssize_t klen,
+ const void *val)
+{
+ cache_hash_entry_t **hep, *he;
+ const unsigned char *p;
+ unsigned int hash;
+ apr_ssize_t i;
+
+ /*
+ * This is the popular `times 33' hash algorithm which is used by
+ * perl and also appears in Berkeley DB. This is one of the best
+ * known hash functions for strings because it is both computed
+ * very fast and distributes very well.
+ *
+ * The originator may be Dan Bernstein but the code in Berkeley DB
+ * cites Chris Torek as the source. The best citation I have found
+ * is "Chris Torek, Hash function for text in C, Usenet message
+ * <27038@mimsy.umd.edu> in comp.lang.c , October, 1990." in Rich
+ * Salz's USENIX 1992 paper about INN which can be found at
+ * <http://citeseer.nj.nec.com/salz92internetnews.html>.
+ *
+ * The magic of number 33, i.e. why it works better than many other
+ * constants, prime or not, has never been adequately explained by
+ * anyone. So I try an explanation: if one experimentally tests all
+ * multipliers between 1 and 256 (as I did while writing a low-level
+ * data structure library some time ago) one detects that even
+ * numbers are not useable at all. The remaining 128 odd numbers
+ * (except for the number 1) work more or less all equally well.
+ * They all distribute in an acceptable way and this way fill a hash
+ * table with an average percent of approx. 86%.
+ *
+ * If one compares the chi^2 values of the variants (see
+ * Bob Jenkins ``Hashing Frequently Asked Questions'' at
+ * http://burtleburtle.net/bob/hash/hashfaq.html for a description
+ * of chi^2), the number 33 not even has the best value. But the
+ * number 33 and a few other equally good numbers like 17, 31, 63,
+ * 127 and 129 have nevertheless a great advantage to the remaining
+ * numbers in the large set of possible multipliers: their multiply
+ * operation can be replaced by a faster operation based on just one
+ * shift plus either a single addition or subtraction operation. And
+ * because a hash function has to both distribute good _and_ has to
+ * be very fast to compute, those few numbers should be preferred.
+ *
+ * -- Ralf S. Engelschall <rse@engelschall.com>
+ */
+ hash = 0;
+ if (klen == CACHE_HASH_KEY_STRING) {
+ for (p = key; *p; p++) {
+ hash = hash * 33 + *p;
+ }
+ klen = p - (const unsigned char *)key;
+ }
+ else {
+ for (p = key, i = klen; i; i--, p++) {
+ hash = hash * 33 + *p;
+ }
+ }
+
+ /* scan linked list */
+ for (hep = &ht->array[hash % ht->max], he = *hep;
+ he;
+ hep = &he->next, he = *hep) {
+ if (he->hash == hash &&
+ he->klen == klen &&
+ memcmp(he->key, key, klen) == 0)
+ break;
+ }
+ if (he || !val)
+ return hep;
+ /* add a new entry for non-NULL values */
+ he = malloc(sizeof(*he));
+ if (!he) {
+ return NULL;
+ }
+ he->next = NULL;
+ he->hash = hash;
+ he->key = key;
+ he->klen = klen;
+ he->val = val;
+ *hep = he;
+ ht->count++;
+ return hep;
+}
+
+CACHE_DECLARE(void *) cache_hash_get(cache_hash_t *ht,
+ const void *key,
+ apr_ssize_t klen)
+{
+ cache_hash_entry_t *he;
+ he = *find_entry(ht, key, klen, NULL);
+ if (he)
+ return (void *)he->val;
+ else
+ return NULL;
+}
+
+CACHE_DECLARE(void *) cache_hash_set(cache_hash_t *ht,
+ const void *key,
+ apr_ssize_t klen,
+ const void *val)
+{
+ cache_hash_entry_t **hep, *tmp;
+ const void *tval;
+ hep = find_entry(ht, key, klen, val);
+ /* If hep == NULL, then the malloc() in find_entry failed */
+ if (hep && *hep) {
+ if (!val) {
+ /* delete entry */
+ tval = (*hep)->val;
+ tmp = *hep;
+ *hep = (*hep)->next;
+ free(tmp);
+ --ht->count;
+ }
+ else {
+ /* replace entry */
+ tval = (*hep)->val;
+ (*hep)->val = val;
+ }
+ /* Return the object just removed from the cache to let the
+ * caller clean it up. Cast the constness away upon return.
+ */
+ return (void *) tval;
+ }
+ /* else key not present and val==NULL */
+ return NULL;
+}
+
+CACHE_DECLARE(int) cache_hash_count(cache_hash_t *ht)
+{
+ return ht->count;
+}