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Diffstat (limited to 'libguile/weak-set.c')
-rw-r--r-- | libguile/weak-set.c | 873 |
1 files changed, 0 insertions, 873 deletions
diff --git a/libguile/weak-set.c b/libguile/weak-set.c deleted file mode 100644 index ef6a5231d..000000000 --- a/libguile/weak-set.c +++ /dev/null @@ -1,873 +0,0 @@ -/* Copyright 2011-2013,2018,2025 - Free Software Foundation, Inc. - - This file is part of Guile. - - Guile is free software: you can redistribute it and/or modify it - under the terms of the GNU Lesser General Public License as published - by the Free Software Foundation, either version 3 of the License, or - (at your option) any later version. - - Guile is distributed in the hope that it will be useful, but WITHOUT - ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or - FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public - License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with Guile. If not, see - <https://www.gnu.org/licenses/>. */ - - - - -#ifdef HAVE_CONFIG_H -# include <config.h> -#endif - -#include <assert.h> -#include <string.h> - -#include "bdw-gc.h" -#include "eval.h" -#include "finalizers.h" -#include "hash.h" -#include "pairs.h" -#include "ports.h" -#include "threads.h" -#include "weak-set.h" - - -/* Weak Sets - - This file implements weak sets. One example of a weak set is the - symbol table, where you want all instances of the `foo' symbol to map - to one object. So when you load a file and it wants a symbol with - the characters "foo", you one up in the table, using custom hash and - equality predicates. Only if one is not found will you bother to - cons one up and intern it. - - Another use case for weak sets is the set of open ports. Guile needs - to be able to flush them all when the process exits, but the set - shouldn't prevent the GC from collecting the port (and thus closing - it). - - Weak sets are implemented using an open-addressed hash table. - Basically this means that there is an array of entries, and the item - is expected to be found the slot corresponding to its hash code, - modulo the length of the array. - - Collisions are handled using linear probing with the Robin Hood - technique. See Pedro Celis' paper, "Robin Hood Hashing": - - http://www.cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf - - The vector of entries is allocated as an "atomic" piece of memory, so - that the GC doesn't trace it. When an item is added to the set, a - disappearing link is registered to its location. If the item is - collected, then that link will be zeroed out. - - An entry is not just an item, though; the hash code is also stored in - the entry. We munge hash codes so that they are never 0. In this - way we can detect removed entries (key of zero but nonzero hash - code), and can then reshuffle elements as needed to maintain the - robin hood ordering. - - Compared to buckets-and-chains hash tables, open addressing has the - advantage that it is very cache-friendly. It also uses less memory. - - Implementation-wise, there are two things to note. - - 1. We assume that hash codes are evenly distributed across the - range of unsigned longs. The actual hash code stored in the - entry is left-shifted by 1 bit (losing 1 bit of hash precision), - and then or'd with 1. In this way we ensure that the hash field - of an occupied entry is nonzero. To map to an index, we - right-shift the hash by one, divide by the size, and take the - remainder. - - 2. Since the "keys" (the objects in the set) are stored in an - atomic region with disappearing links, they need to be accessed - with the GC alloc lock. `copy_weak_entry' will do that for - you. The hash code itself can be read outside the lock, - though. -*/ - - -typedef struct { - unsigned long hash; - scm_t_bits key; -} scm_t_weak_entry; - - -struct weak_entry_data { - scm_t_weak_entry *in; - scm_t_weak_entry *out; -}; - -static void* -do_copy_weak_entry (void *data) -{ - struct weak_entry_data *e = data; - - e->out->hash = e->in->hash; - e->out->key = e->in->key; - - return NULL; -} - -static void -copy_weak_entry (scm_t_weak_entry *src, scm_t_weak_entry *dst) -{ - struct weak_entry_data data; - - data.in = src; - data.out = dst; - - GC_call_with_alloc_lock (do_copy_weak_entry, &data); -} - - -typedef struct { - scm_t_weak_entry *entries; /* the data */ - scm_i_pthread_mutex_t lock; /* the lock */ - unsigned long size; /* total number of slots. */ - unsigned long n_items; /* number of items in set */ - unsigned long lower; /* when to shrink */ - unsigned long upper; /* when to grow */ - int size_index; /* index into hashset_size */ - int min_size_index; /* minimum size_index */ -} scm_t_weak_set; - - -#define SCM_WEAK_SET_P(x) (SCM_HAS_TYP7 (x, scm_tc7_weak_set)) -#define SCM_VALIDATE_WEAK_SET(pos, arg) \ - SCM_MAKE_VALIDATE_MSG (pos, arg, WEAK_SET_P, "weak-set") -#define SCM_WEAK_SET(x) ((scm_t_weak_set *) SCM_CELL_WORD_1 (x)) - - -static unsigned long -hash_to_index (unsigned long hash, unsigned long size) -{ - return (hash >> 1) % size; -} - -static unsigned long -entry_distance (unsigned long hash, unsigned long k, unsigned long size) -{ - unsigned long origin = hash_to_index (hash, size); - - if (k >= origin) - return k - origin; - else - /* The other key was displaced and wrapped around. */ - return size - origin + k; -} - -#ifndef HAVE_GC_MOVE_DISAPPEARING_LINK -static void -GC_move_disappearing_link (void **from, void **to) -{ - GC_unregister_disappearing_link (from); - SCM_I_REGISTER_DISAPPEARING_LINK (to, *to); -} -#endif - -static void -move_weak_entry (scm_t_weak_entry *from, scm_t_weak_entry *to) -{ - if (from->hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (from, ©); - to->hash = copy.hash; - to->key = copy.key; - - if (copy.key && SCM_HEAP_OBJECT_P (SCM_PACK (copy.key))) - GC_move_disappearing_link ((void **) &from->key, (void **) &to->key); - } - else - { - to->hash = 0; - to->key = 0; - } -} - -static void -rob_from_rich (scm_t_weak_set *set, unsigned long k) -{ - unsigned long empty, size; - - size = set->size; - - /* If we are to free up slot K in the set, we need room to do so. */ - assert (set->n_items < size); - - empty = k; - do - empty = (empty + 1) % size; - /* Here we access key outside the lock. Is this a problem? At first - glance, I wouldn't think so. */ - while (set->entries[empty].key); - - do - { - unsigned long last = empty ? (empty - 1) : (size - 1); - move_weak_entry (&set->entries[last], &set->entries[empty]); - empty = last; - } - while (empty != k); - - /* Just for sanity. */ - set->entries[empty].hash = 0; - set->entries[empty].key = 0; -} - -static void -give_to_poor (scm_t_weak_set *set, unsigned long k) -{ - /* Slot K was just freed up; possibly shuffle others down. */ - unsigned long size = set->size; - - while (1) - { - unsigned long next = (k + 1) % size; - unsigned long hash; - scm_t_weak_entry copy; - - hash = set->entries[next].hash; - - if (!hash || hash_to_index (hash, size) == next) - break; - - copy_weak_entry (&set->entries[next], ©); - - if (!copy.key) - /* Lost weak reference. */ - { - give_to_poor (set, next); - set->n_items--; - continue; - } - - move_weak_entry (&set->entries[next], &set->entries[k]); - - k = next; - } - - /* We have shuffled down any entries that should be shuffled down; now - free the end. */ - set->entries[k].hash = 0; - set->entries[k].key = 0; -} - - - - -/* Growing or shrinking is triggered when the load factor - * - * L = N / S (N: number of items in set, S: bucket vector length) - * - * passes an upper limit of 0.9 or a lower limit of 0.2. - * - * The implementation stores the upper and lower number of items which - * trigger a resize in the hashset object. - * - * Possible hash set sizes (primes) are stored in the array - * hashset_size. - */ - -static unsigned long hashset_size[] = { - 31, 61, 113, 223, 443, 883, 1759, 3517, 7027, 14051, 28099, 56197, 112363, - 224717, 449419, 898823, 1797641, 3595271, 7190537, 14381041, 28762081, - 57524111, 115048217, 230096423 -}; - -#define HASHSET_SIZE_N (sizeof(hashset_size)/sizeof(unsigned long)) - -static int -compute_size_index (scm_t_weak_set *set) -{ - int i = set->size_index; - - if (set->n_items < set->lower) - { - /* rehashing is not triggered when i <= min_size */ - do - --i; - while (i > set->min_size_index - && set->n_items < hashset_size[i] / 5); - } - else if (set->n_items > set->upper) - { - ++i; - if (i >= HASHSET_SIZE_N) - /* The biggest size currently is 230096423, which for a 32-bit - machine will occupy 1.5GB of memory at a load of 80%. There - is probably something better to do here, but if you have a - weak map of that size, you are hosed in any case. */ - abort (); - } - - return i; -} - -static int -is_acceptable_size_index (scm_t_weak_set *set, int size_index) -{ - int computed = compute_size_index (set); - - if (size_index == computed) - /* We were going to grow or shrink, and allocating the new vector - didn't change the target size. */ - return 1; - - if (size_index == computed + 1) - { - /* We were going to enlarge the set, but allocating the new - vector finalized some objects, making an enlargement - unnecessary. It might still be a good idea to use the larger - set, though. (This branch also gets hit if, while allocating - the vector, some other thread was actively removing items from - the set. That is less likely, though.) */ - unsigned long new_lower = hashset_size[size_index] / 5; - - return set->size > new_lower; - } - - if (size_index == computed - 1) - { - /* We were going to shrink the set, but when we dropped the lock - to allocate the new vector, some other thread added elements to - the set. */ - return 0; - } - - /* The computed size differs from our newly allocated size by more - than one size index -- recalculate. */ - return 0; -} - -static void -resize_set (scm_t_weak_set *set) -{ - scm_t_weak_entry *old_entries, *new_entries; - int new_size_index; - unsigned long old_size, new_size, old_k; - - do - { - new_size_index = compute_size_index (set); - if (new_size_index == set->size_index) - return; - new_size = hashset_size[new_size_index]; - } - while (!is_acceptable_size_index (set, new_size_index)); - - new_entries = scm_gc_malloc_pointerless (new_size * sizeof (scm_t_weak_entry), - "weak set"); - old_entries = set->entries; - old_size = set->size; - - memset (new_entries, 0, new_size * sizeof(scm_t_weak_entry)); - - set->size_index = new_size_index; - set->size = new_size; - if (new_size_index <= set->min_size_index) - set->lower = 0; - else - set->lower = new_size / 5; - set->upper = 9 * new_size / 10; - set->n_items = 0; - set->entries = new_entries; - - for (old_k = 0; old_k < old_size; old_k++) - { - scm_t_weak_entry copy; - unsigned long new_k, distance; - - if (!old_entries[old_k].hash) - continue; - - copy_weak_entry (&old_entries[old_k], ©); - - if (!copy.key) - continue; - - new_k = hash_to_index (copy.hash, new_size); - - for (distance = 0; ; distance++, new_k = (new_k + 1) % new_size) - { - unsigned long other_hash = new_entries[new_k].hash; - - if (!other_hash) - /* Found an empty entry. */ - break; - - /* Displace the entry if our distance is less, otherwise keep - looking. */ - if (entry_distance (other_hash, new_k, new_size) < distance) - { - rob_from_rich (set, new_k); - break; - } - } - - set->n_items++; - new_entries[new_k].hash = copy.hash; - new_entries[new_k].key = copy.key; - - if (SCM_HEAP_OBJECT_P (SCM_PACK (copy.key))) - SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &new_entries[new_k].key, - (void *) new_entries[new_k].key); - } -} - -/* Run from a finalizer via do_vacuum_weak_set, this function runs over - the whole table, removing lost weak references, reshuffling the set - as it goes. It might resize the set if it reaps enough entries. */ -static void -vacuum_weak_set (scm_t_weak_set *set) -{ - scm_t_weak_entry *entries = set->entries; - unsigned long size = set->size; - unsigned long k; - - for (k = 0; k < size; k++) - { - unsigned long hash = entries[k].hash; - - if (hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (&entries[k], ©); - - if (!copy.key) - /* Lost weak reference; reshuffle. */ - { - give_to_poor (set, k); - set->n_items--; - } - } - } - - if (set->n_items < set->lower) - resize_set (set); -} - - - - -static SCM -weak_set_lookup (scm_t_weak_set *set, unsigned long hash, - scm_t_set_predicate_fn pred, void *closure, - SCM dflt) -{ - unsigned long k, distance, size; - scm_t_weak_entry *entries; - - size = set->size; - entries = set->entries; - - hash = (hash << 1) | 0x1; - k = hash_to_index (hash, size); - - for (distance = 0; distance < size; distance++, k = (k + 1) % size) - { - unsigned long other_hash; - - retry: - other_hash = entries[k].hash; - - if (!other_hash) - /* Not found. */ - return dflt; - - if (hash == other_hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (&entries[k], ©); - - if (!copy.key) - /* Lost weak reference; reshuffle. */ - { - give_to_poor (set, k); - set->n_items--; - goto retry; - } - - if (pred (SCM_PACK (copy.key), closure)) - /* Found. */ - return SCM_PACK (copy.key); - } - - /* If the entry's distance is less, our key is not in the set. */ - if (entry_distance (other_hash, k, size) < distance) - return dflt; - } - - /* If we got here, then we were unfortunate enough to loop through the - whole set. Shouldn't happen, but hey. */ - return dflt; -} - - -static SCM -weak_set_add_x (scm_t_weak_set *set, unsigned long hash, - scm_t_set_predicate_fn pred, void *closure, - SCM obj) -{ - unsigned long k, distance, size; - scm_t_weak_entry *entries; - - size = set->size; - entries = set->entries; - - hash = (hash << 1) | 0x1; - k = hash_to_index (hash, size); - - for (distance = 0; ; distance++, k = (k + 1) % size) - { - unsigned long other_hash; - - retry: - other_hash = entries[k].hash; - - if (!other_hash) - /* Found an empty entry. */ - break; - - if (other_hash == hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (&entries[k], ©); - - if (!copy.key) - /* Lost weak reference; reshuffle. */ - { - give_to_poor (set, k); - set->n_items--; - goto retry; - } - - if (pred (SCM_PACK (copy.key), closure)) - /* Found an entry with this key. */ - return SCM_PACK (copy.key); - } - - if (set->n_items > set->upper) - /* Full set, time to resize. */ - { - vacuum_weak_set (set); - resize_set (set); - return weak_set_add_x (set, hash >> 1, pred, closure, obj); - } - - /* Displace the entry if our distance is less, otherwise keep - looking. */ - if (entry_distance (other_hash, k, size) < distance) - { - rob_from_rich (set, k); - break; - } - } - - set->n_items++; - entries[k].hash = hash; - entries[k].key = SCM_UNPACK (obj); - - if (SCM_HEAP_OBJECT_P (obj)) - SCM_I_REGISTER_DISAPPEARING_LINK ((void **) &entries[k].key, - (void *) SCM2PTR (obj)); - - return obj; -} - - -static void -weak_set_remove_x (scm_t_weak_set *set, unsigned long hash, - scm_t_set_predicate_fn pred, void *closure) -{ - unsigned long k, distance, size; - scm_t_weak_entry *entries; - - size = set->size; - entries = set->entries; - - hash = (hash << 1) | 0x1; - k = hash_to_index (hash, size); - - for (distance = 0; distance < size; distance++, k = (k + 1) % size) - { - unsigned long other_hash; - - retry: - other_hash = entries[k].hash; - - if (!other_hash) - /* Not found. */ - return; - - if (other_hash == hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (&entries[k], ©); - - if (!copy.key) - /* Lost weak reference; reshuffle. */ - { - give_to_poor (set, k); - set->n_items--; - goto retry; - } - - if (pred (SCM_PACK (copy.key), closure)) - /* Found an entry with this key. */ - { - entries[k].hash = 0; - entries[k].key = 0; - - if (SCM_HEAP_OBJECT_P (SCM_PACK (copy.key))) - GC_unregister_disappearing_link ((void **) &entries[k].key); - - if (--set->n_items < set->lower) - resize_set (set); - else - give_to_poor (set, k); - - return; - } - } - - /* If the entry's distance is less, our key is not in the set. */ - if (entry_distance (other_hash, k, size) < distance) - return; - } -} - - - -static SCM -make_weak_set (unsigned long k) -{ - scm_t_weak_set *set; - - int i = 0, n = k ? k : 31; - while (i + 1 < HASHSET_SIZE_N && n > hashset_size[i]) - ++i; - n = hashset_size[i]; - - set = scm_gc_malloc (sizeof (*set), "weak-set"); - set->entries = scm_gc_malloc_pointerless (n * sizeof(scm_t_weak_entry), - "weak-set"); - memset (set->entries, 0, n * sizeof(scm_t_weak_entry)); - set->n_items = 0; - set->size = n; - set->lower = 0; - set->upper = 9 * n / 10; - set->size_index = i; - set->min_size_index = i; - scm_i_pthread_mutex_init (&set->lock, NULL); - - return scm_cell (scm_tc7_weak_set, (scm_t_bits)set); -} - -void -scm_i_weak_set_print (SCM exp, SCM port, scm_print_state *pstate) -{ - scm_puts ("#<", port); - scm_puts ("weak-set ", port); - scm_uintprint (SCM_WEAK_SET (exp)->n_items, 10, port); - scm_putc ('/', port); - scm_uintprint (SCM_WEAK_SET (exp)->size, 10, port); - scm_puts (">", port); -} - -SCM -scm_c_make_weak_set (unsigned long k) -{ - SCM ret; - - ret = make_weak_set (k); - - return ret; -} - -SCM -scm_weak_set_p (SCM obj) -{ - return scm_from_bool (SCM_WEAK_SET_P (obj)); -} - -SCM -scm_weak_set_clear_x (SCM set) -{ - scm_t_weak_set *s = SCM_WEAK_SET (set); - - scm_i_pthread_mutex_lock (&s->lock); - - memset (s->entries, 0, sizeof (scm_t_weak_entry) * s->size); - s->n_items = 0; - - scm_i_pthread_mutex_unlock (&s->lock); - - return SCM_UNSPECIFIED; -} - -SCM -scm_c_weak_set_lookup (SCM set, unsigned long raw_hash, - scm_t_set_predicate_fn pred, - void *closure, SCM dflt) -{ - SCM ret; - scm_t_weak_set *s = SCM_WEAK_SET (set); - - scm_i_pthread_mutex_lock (&s->lock); - - ret = weak_set_lookup (s, raw_hash, pred, closure, dflt); - - scm_i_pthread_mutex_unlock (&s->lock); - - return ret; -} - -SCM -scm_c_weak_set_add_x (SCM set, unsigned long raw_hash, - scm_t_set_predicate_fn pred, - void *closure, SCM obj) -{ - SCM ret; - scm_t_weak_set *s = SCM_WEAK_SET (set); - - scm_i_pthread_mutex_lock (&s->lock); - - ret = weak_set_add_x (s, raw_hash, pred, closure, obj); - - scm_i_pthread_mutex_unlock (&s->lock); - - return ret; -} - -void -scm_c_weak_set_remove_x (SCM set, unsigned long raw_hash, - scm_t_set_predicate_fn pred, - void *closure) -{ - scm_t_weak_set *s = SCM_WEAK_SET (set); - - scm_i_pthread_mutex_lock (&s->lock); - - weak_set_remove_x (s, raw_hash, pred, closure); - - scm_i_pthread_mutex_unlock (&s->lock); -} - -static int -eq_predicate (SCM x, void *closure) -{ - return scm_is_eq (x, SCM_PACK_POINTER (closure)); -} - -SCM -scm_weak_set_add_x (SCM set, SCM obj) -{ - return scm_c_weak_set_add_x (set, scm_ihashq (obj, -1), - eq_predicate, SCM_UNPACK_POINTER (obj), obj); -} - -SCM -scm_weak_set_remove_x (SCM set, SCM obj) -{ - scm_c_weak_set_remove_x (set, scm_ihashq (obj, -1), - eq_predicate, SCM_UNPACK_POINTER (obj)); - - return SCM_UNSPECIFIED; -} - -SCM -scm_c_weak_set_fold (scm_t_set_fold_fn proc, void *closure, - SCM init, SCM set) -{ - scm_t_weak_set *s; - scm_t_weak_entry *entries; - unsigned long k, size; - - s = SCM_WEAK_SET (set); - - scm_i_pthread_mutex_lock (&s->lock); - - size = s->size; - entries = s->entries; - - for (k = 0; k < size; k++) - { - if (entries[k].hash) - { - scm_t_weak_entry copy; - - copy_weak_entry (&entries[k], ©); - - if (copy.key) - { - /* Release set lock while we call the function. */ - scm_i_pthread_mutex_unlock (&s->lock); - init = proc (closure, SCM_PACK (copy.key), init); - scm_i_pthread_mutex_lock (&s->lock); - } - } - } - - scm_i_pthread_mutex_unlock (&s->lock); - - return init; -} - -static SCM -fold_trampoline (void *closure, SCM item, SCM init) -{ - return scm_call_2 (SCM_PACK_POINTER (closure), item, init); -} - -SCM -scm_weak_set_fold (SCM proc, SCM init, SCM set) -{ - return scm_c_weak_set_fold (fold_trampoline, SCM_UNPACK_POINTER (proc), init, set); -} - -static SCM -for_each_trampoline (void *closure, SCM item, SCM seed) -{ - scm_call_1 (SCM_PACK_POINTER (closure), item); - return seed; -} - -SCM -scm_weak_set_for_each (SCM proc, SCM set) -{ - scm_c_weak_set_fold (for_each_trampoline, SCM_UNPACK_POINTER (proc), SCM_BOOL_F, set); - - return SCM_UNSPECIFIED; -} - -static SCM -map_trampoline (void *closure, SCM item, SCM seed) -{ - return scm_cons (scm_call_1 (SCM_PACK_POINTER (closure), item), seed); -} - -SCM -scm_weak_set_map_to_list (SCM proc, SCM set) -{ - return scm_c_weak_set_fold (map_trampoline, SCM_UNPACK_POINTER (proc), SCM_EOL, set); -} - - -void -scm_init_weak_set () -{ -#include "weak-set.x" -} |