Date: Sun, 27 Dec 2015 07:50:12 +0000 (UTC) From: Ed Schouten <ed@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r292767 - in head: include lib/libc/stdlib Message-ID: <201512270750.tBR7oCrv055290@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: ed Date: Sun Dec 27 07:50:11 2015 New Revision: 292767 URL: https://svnweb.freebsd.org/changeset/base/292767 Log: Replace implementation of hsearch() by one that scales. Traditionally the hcreate() function creates a hash table that uses chaining, using a fixed user-provided size. The problem with this approach is that this often either wastes memory (table too big) or yields bad performance (table too small). For applications it may not always be easy to estimate the right hash table size. A fixed number only increases performance compared to a linked list by a constant factor. This problem can be solved easily by dynamically resizing the hash table. If the size of the hash table is at least doubled, this has no negative on the running time complexity. If a dynamically sized hash table is used, we can also switch to using open addressing instead of chaining, which has the advantage of just using a single allocation for the entire table, instead of allocating many small objects. Finally, a problem with the existing implementation is that its deterministic algorithm for hashing makes it possible to come up with fixed patterns to trigger an excessive number of collisions. We can easily solve this by using FNV-1a as a hashing algorithm in combination with a randomly generated offset basis. Measurements have shown that this implementation is about 20-25% faster than the existing implementation (even if the existing implementation is given an excessive number of buckets). Though it allocates more memory through malloc() than the old implementation (between 4-8 pointers per used entry instead of 3), process memory use is similar to the old implementation as if the estimated size was underestimated by a factor 10. This is due to the fact that malloc() needs to perform less bookkeeping. Reviewed by: jilles, pfg Obtained from: https://github.com/NuxiNL/cloudlibc Differential Revision: https://reviews.freebsd.org/D4644 Added: head/lib/libc/stdlib/hcreate_r.c (contents, props changed) head/lib/libc/stdlib/hdestroy_r.c (contents, props changed) head/lib/libc/stdlib/hsearch.h (contents, props changed) head/lib/libc/stdlib/hsearch_r.c (contents, props changed) Replaced: head/lib/libc/stdlib/hcreate.c (contents, props changed) Modified: head/include/search.h head/lib/libc/stdlib/Makefile.inc head/lib/libc/stdlib/hcreate.3 Modified: head/include/search.h ============================================================================== --- head/include/search.h Sun Dec 27 07:39:44 2015 (r292766) +++ head/include/search.h Sun Dec 27 07:50:11 2015 (r292767) @@ -47,11 +47,8 @@ struct que_elem { #endif #if __BSD_VISIBLE -struct _ENTRY; struct hsearch_data { - struct _ENTRY *table; - size_t size; - size_t filled; + struct __hsearch *__hsearch; }; #endif Modified: head/lib/libc/stdlib/Makefile.inc ============================================================================== --- head/lib/libc/stdlib/Makefile.inc Sun Dec 27 07:39:44 2015 (r292766) +++ head/lib/libc/stdlib/Makefile.inc Sun Dec 27 07:50:11 2015 (r292767) @@ -6,7 +6,8 @@ MISRCS+=_Exit.c a64l.c abort.c abs.c atexit.c atof.c atoi.c atol.c atoll.c \ bsearch.c div.c exit.c getenv.c getopt.c getopt_long.c \ - getsubopt.c hcreate.c heapsort.c heapsort_b.c imaxabs.c imaxdiv.c \ + getsubopt.c hcreate.c hcreate_r.c hdestroy_r.c heapsort.c heapsort_b.c \ + hsearch_r.c imaxabs.c imaxdiv.c \ insque.c l64a.c labs.c ldiv.c llabs.c lldiv.c lsearch.c \ merge.c mergesort_b.c ptsname.c qsort.c qsort_r.c quick_exit.c \ radixsort.c rand.c \ Modified: head/lib/libc/stdlib/hcreate.3 ============================================================================== --- head/lib/libc/stdlib/hcreate.3 Sun Dec 27 07:39:44 2015 (r292766) +++ head/lib/libc/stdlib/hcreate.3 Sun Dec 27 07:50:11 2015 (r292767) @@ -28,7 +28,7 @@ .\" .\" $FreeBSD$ .\" -.Dd July 21, 2014 +.Dd December 26, 2015 .Dt HCREATE 3 .Os .Sh NAME @@ -76,8 +76,8 @@ The .Fa nel argument is an estimate of the maximum number of entries that the table should contain. -This number may be adjusted upward by the -algorithm in order to obtain certain mathematically favorable circumstances. +As this implementation resizes the hash table dynamically, +this argument is ignored. .Pp The .Fn hdestroy @@ -274,8 +274,6 @@ functions will fail if: .Bl -tag -width Er .It Bq Er ENOMEM Insufficient memory is available. -.It Bq Er EINVAL -A table already exists. .El .Pp The Added: head/lib/libc/stdlib/hcreate.c ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ head/lib/libc/stdlib/hcreate.c Sun Dec 27 07:50:11 2015 (r292767) @@ -0,0 +1,73 @@ +/*- + * Copyright (c) 2015 Nuxi, https://nuxi.nl/ + * + * 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. + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +#include <search.h> +#include <stdbool.h> +#include <stddef.h> + +/* + * Thread unsafe interface: use a single process-wide hash table and + * forward calls to *_r() functions. + */ + +static struct hsearch_data global_hashtable; +static bool global_hashtable_initialized = false; + +int +hcreate(size_t nel) +{ + + return (1); +} + +void +hdestroy(void) +{ + + /* Destroy global hash table if present. */ + if (global_hashtable_initialized) { + hdestroy_r(&global_hashtable); + global_hashtable_initialized = false; + } +} + +ENTRY * +hsearch(ENTRY item, ACTION action) +{ + ENTRY *retval; + + /* Create global hash table if needed. */ + if (!global_hashtable_initialized) { + if (hcreate_r(0, &global_hashtable) == 0) + return (NULL); + global_hashtable_initialized = true; + } + if (hsearch_r(item, action, &retval, &global_hashtable) == 0) + return (NULL); + return (retval); +} Added: head/lib/libc/stdlib/hcreate_r.c ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ head/lib/libc/stdlib/hcreate_r.c Sun Dec 27 07:50:11 2015 (r292767) @@ -0,0 +1,63 @@ +/*- + * Copyright (c) 2015 Nuxi, https://nuxi.nl/ + * + * 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. + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +#include <search.h> +#include <stdlib.h> + +#include "hsearch.h" + +int +hcreate_r(size_t nel, struct hsearch_data *htab) +{ + struct __hsearch *hsearch; + + /* + * Allocate a hash table object. Ignore the provided hint and start + * off with a table of sixteen entries. In most cases this hint is + * just a wild guess. Resizing the table dynamically if the use + * increases a threshold does not affect the worst-case running time. + */ + hsearch = malloc(sizeof(*hsearch)); + if (hsearch == NULL) + return 0; + hsearch->entries = calloc(16, sizeof(ENTRY)); + if (hsearch->entries == NULL) { + free(hsearch); + return 0; + } + + /* + * Pick a random initialization for the FNV-1a hashing. This makes it + * hard to come up with a fixed set of keys to force hash collisions. + */ + arc4random_buf(&hsearch->offset_basis, sizeof(hsearch->offset_basis)); + hsearch->index_mask = 0xf; + hsearch->entries_used = 0; + htab->__hsearch = hsearch; + return 1; +} Added: head/lib/libc/stdlib/hdestroy_r.c ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ head/lib/libc/stdlib/hdestroy_r.c Sun Dec 27 07:50:11 2015 (r292767) @@ -0,0 +1,43 @@ +/*- + * Copyright (c) 2015 Nuxi, https://nuxi.nl/ + * + * 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. + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +#include <search.h> +#include <stdlib.h> + +#include "hsearch.h" + +void +hdestroy_r(struct hsearch_data *htab) +{ + struct __hsearch *hsearch; + + /* Free hash table object and its entries. */ + hsearch = htab->__hsearch; + free(hsearch->entries); + free(hsearch); +} Added: head/lib/libc/stdlib/hsearch.h ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ head/lib/libc/stdlib/hsearch.h Sun Dec 27 07:50:11 2015 (r292767) @@ -0,0 +1,40 @@ +/*- + * Copyright (c) 2015 Nuxi, https://nuxi.nl/ + * + * 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. + * + * $FreeBSD$ + */ + +#ifndef HSEARCH_H +#define HSEARCH_H + +#include <search.h> + +struct __hsearch { + size_t offset_basis; /* Initial value for FNV-1a hashing. */ + size_t index_mask; /* Bitmask for indexing the table. */ + size_t entries_used; /* Number of entries currently used. */ + ENTRY *entries; /* Hash table entries. */ +}; + +#endif Added: head/lib/libc/stdlib/hsearch_r.c ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ head/lib/libc/stdlib/hsearch_r.c Sun Dec 27 07:50:11 2015 (r292767) @@ -0,0 +1,150 @@ +/*- + * Copyright (c) 2015 Nuxi, https://nuxi.nl/ + * + * 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. + */ + +#include <sys/cdefs.h> +__FBSDID("$FreeBSD$"); + +#include <errno.h> +#include <limits.h> +#include <search.h> +#include <stdint.h> +#include <stdlib.h> +#include <string.h> + +#include "hsearch.h" + +/* + * Look up an unused entry in the hash table for a given hash. For this + * implementation we use quadratic probing. Quadratic probing has the + * advantage of preventing primary clustering. + */ +static ENTRY * +hsearch_lookup_free(struct __hsearch *hsearch, size_t hash) +{ + size_t index, i; + + for (index = hash, i = 0;; index += ++i) { + ENTRY *entry = &hsearch->entries[index & hsearch->index_mask]; + if (entry->key == NULL) + return (entry); + } +} + +/* + * Computes an FNV-1a hash of the key. Depending on the pointer size, this + * either uses the 32- or 64-bit FNV prime. + */ +static size_t +hsearch_hash(size_t offset_basis, const char *str) +{ + size_t hash; + + hash = offset_basis; + while (*str != '\0') { + hash ^= (uint8_t)*str++; + if (sizeof(size_t) * CHAR_BIT <= 32) + hash *= UINT32_C(16777619); + else + hash *= UINT64_C(1099511628211); + } + return (hash); +} + +int +hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab) +{ + struct __hsearch *hsearch; + ENTRY *entry, *old_entries, *new_entries; + size_t hash, index, i, old_hash, old_count, new_count; + + hsearch = htab->__hsearch; + hash = hsearch_hash(hsearch->offset_basis, item.key); + + /* + * Search the hash table for an existing entry for this key. + * Stop searching if we run into an unused hash table entry. + */ + for (index = hash, i = 0;; index += ++i) { + entry = &hsearch->entries[index & hsearch->index_mask]; + if (entry->key == NULL) + break; + if (strcmp(entry->key, item.key) == 0) { + *retval = entry; + return (1); + } + } + + /* Only perform the insertion if action is set to ENTER. */ + if (action == FIND) { + errno = ESRCH; + return (0); + } + + if (hsearch->entries_used * 2 >= hsearch->index_mask) { + /* Preserve the old hash table entries. */ + old_count = hsearch->index_mask + 1; + old_entries = hsearch->entries; + + /* + * Allocate and install a new table if insertion would + * yield a hash table that is more than 50% used. By + * using 50% as a threshold, a lookup will only take up + * to two steps on average. + */ + new_count = (hsearch->index_mask + 1) * 2; + new_entries = calloc(new_count, sizeof(ENTRY)); + if (new_entries == NULL) + return (0); + hsearch->entries = new_entries; + hsearch->index_mask = new_count - 1; + + /* Copy over the entries from the old table to the new table. */ + for (i = 0; i < old_count; ++i) { + entry = &old_entries[i]; + if (entry->key != NULL) { + old_hash = hsearch_hash(hsearch->offset_basis, + entry->key); + *hsearch_lookup_free(hsearch, old_hash) = + *entry; + } + } + + /* Destroy the old hash table entries. */ + free(old_entries); + + /* + * Perform a new lookup for a free table entry, so that + * we insert the entry into the new hash table. + */ + hsearch = htab->__hsearch; + entry = hsearch_lookup_free(hsearch, hash); + } + + /* Insert the new entry into the hash table. */ + *entry = item; + ++hsearch->entries_used; + *retval = entry; + return (1); +}
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201512270750.tBR7oCrv055290>