Neels Hofmeyr | 0e8df1c | 2019-02-11 20:32:25 +0100 | [diff] [blame] | 1 | /*! \file use_count.c |
| 2 | * Generic object usage counter Implementation (get, put and deallocate on zero count). |
| 3 | */ |
| 4 | /* |
| 5 | * (C) 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de> |
| 6 | * |
| 7 | * All Rights Reserved |
| 8 | * |
| 9 | * Author: Neels Hofmeyr <neels@hofmeyr.de> |
| 10 | * |
| 11 | * SPDX-License-Identifier: GPL-2.0+ |
| 12 | * |
| 13 | * This program is free software; you can redistribute it and/or modify |
| 14 | * it under the terms of the GNU General Public License as published by |
| 15 | * the Free Software Foundation; either version 2 of the License, or |
| 16 | * (at your option) any later version. |
| 17 | * |
| 18 | * This program is distributed in the hope that it will be useful, |
| 19 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 20 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 21 | * GNU General Public License for more details. |
| 22 | * |
| 23 | * You should have received a copy of the GNU General Public License along |
| 24 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 25 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 26 | */ |
| 27 | |
| 28 | #include <errno.h> |
| 29 | #include <inttypes.h> |
| 30 | #include <string.h> |
| 31 | |
| 32 | #include <osmocom/core/linuxlist.h> |
| 33 | #include <osmocom/core/utils.h> |
| 34 | #include <osmocom/core/use_count.h> |
| 35 | |
| 36 | /*! \addtogroup use_count |
| 37 | * |
| 38 | * Generic object usage counter (get, put and deallocate on zero count). |
| 39 | * |
| 40 | * For an example and a detailed description, see struct osmo_use_count. |
| 41 | * |
| 42 | * @{ |
| 43 | * \file use_count.c |
| 44 | */ |
| 45 | |
| 46 | /*! Add two int32_t but make sure to min- and max-clamp at INT32_MIN and INT32_MAX, respectively. */ |
| 47 | static inline bool count_safe(int32_t *val_p, int32_t add) |
| 48 | { |
| 49 | int32_t val = *val_p; |
| 50 | |
| 51 | /* A simpler implementation would just let the integer overflow and compare with previous value afterwards, but |
| 52 | * that causes runtime errors in the address sanitizer. So let's just do this without tricks. */ |
| 53 | if (add < 0 && val < 0 && val - INT32_MIN < -add) { |
| 54 | *val_p = INT32_MIN; |
| 55 | return false; |
| 56 | } |
| 57 | |
| 58 | if (add > 0 && val > 0 && INT32_MAX - val < add) { |
| 59 | *val_p = INT32_MAX; |
| 60 | return false; |
| 61 | } |
| 62 | |
| 63 | *val_p = val + add; |
| 64 | return true; |
| 65 | } |
| 66 | |
| 67 | /*! Return the sum of all use counts, min- and max-clamped at INT32_MIN and INT32_MAX. |
| 68 | * \param[in] uc Use counts to sum up. |
| 69 | * \return Accumulated counts, or 0 if uc is NULL. |
| 70 | */ |
| 71 | int32_t osmo_use_count_total(const struct osmo_use_count *uc) |
| 72 | { |
| 73 | struct osmo_use_count_entry *e; |
| 74 | int32_t total = 0; |
| 75 | |
| 76 | if (!uc || !uc->use_counts.next) |
| 77 | return 0; |
| 78 | |
| 79 | llist_for_each_entry(e, &uc->use_counts, entry) { |
| 80 | count_safe(&total, e->count); |
| 81 | } |
| 82 | return total; |
| 83 | } |
| 84 | |
| 85 | /*! Return use count by a single use token. |
| 86 | * \param[in] uc Use counts to look up in. |
| 87 | * \param[in] use Use token. |
| 88 | * \return Use count, or 0 if uc is NULL or use token is not present. |
| 89 | */ |
| 90 | int32_t osmo_use_count_by(const struct osmo_use_count *uc, const char *use) |
| 91 | { |
| 92 | const struct osmo_use_count_entry *e; |
| 93 | if (!uc) |
| 94 | return 0; |
| 95 | e = osmo_use_count_find(uc, use); |
| 96 | if (!e) |
| 97 | return 0; |
| 98 | return e->count; |
| 99 | } |
| 100 | |
| 101 | /*! Write a comprehensive listing of use counts to a string buffer. |
| 102 | * Reads like "12 (3*barring,fighting,8*kungfoo)". |
| 103 | * \param[inout] buf Destination buffer. |
| 104 | * \param[in] buf_len sizeof(buf). |
| 105 | * \param[in] uc Use counts to print. |
| 106 | * \return buf, always nul-terminated (except when buf_len < 1). |
| 107 | */ |
| 108 | const char *osmo_use_count_name_buf(char *buf, size_t buf_len, const struct osmo_use_count *uc) |
| 109 | { |
| 110 | int32_t count = osmo_use_count_total(uc); |
| 111 | struct osmo_strbuf sb = { .buf = buf, .len = buf_len }; |
| 112 | struct osmo_use_count_entry *e; |
| 113 | bool first; |
| 114 | |
| 115 | OSMO_STRBUF_PRINTF(sb, "%" PRId32 " (", count); |
| 116 | |
| 117 | first = true; |
| 118 | llist_for_each_entry(e, &uc->use_counts, entry) { |
| 119 | if (!e->count) |
| 120 | continue; |
| 121 | if (!first) |
| 122 | OSMO_STRBUF_PRINTF(sb, ","); |
| 123 | first = false; |
| 124 | if (e->count != 1) |
| 125 | OSMO_STRBUF_PRINTF(sb, "%" PRId32 "*", e->count); |
| 126 | OSMO_STRBUF_PRINTF(sb, "%s", e->use ? : "NULL"); |
| 127 | } |
| 128 | if (first) |
| 129 | OSMO_STRBUF_PRINTF(sb, "-"); |
| 130 | OSMO_STRBUF_PRINTF(sb, ")"); |
| 131 | return buf; |
| 132 | } |
| 133 | |
| 134 | /* Return a use token's use count entry -- probably you want osmo_use_count_by() instead. |
| 135 | * \param[in] uc Use counts to look up in. |
| 136 | * \param[in] use Use token. |
| 137 | * \return matching entry, or NULL if not present. |
| 138 | */ |
| 139 | struct osmo_use_count_entry *osmo_use_count_find(const struct osmo_use_count *uc, const char *use) |
| 140 | { |
| 141 | struct osmo_use_count_entry *e; |
| 142 | if (!uc->use_counts.next) |
| 143 | return NULL; |
| 144 | llist_for_each_entry(e, &uc->use_counts, entry) { |
| 145 | if (e->use == use || (use && e->use && !strcmp(e->use, use))) |
| 146 | return e; |
| 147 | } |
| 148 | return NULL; |
| 149 | } |
| 150 | |
| 151 | /*! Find a use count entry that currently has zero count, and re-use that for this new use token. */ |
| 152 | static struct osmo_use_count_entry *osmo_use_count_repurpose_zero_entry(struct osmo_use_count *uc, const char *use) |
| 153 | { |
| 154 | struct osmo_use_count_entry *e; |
| 155 | if (!uc->use_counts.next) |
| 156 | return NULL; |
| 157 | llist_for_each_entry(e, &uc->use_counts, entry) { |
| 158 | if (!e->count) { |
| 159 | e->use = use; |
| 160 | return e; |
| 161 | } |
| 162 | } |
| 163 | return NULL; |
| 164 | } |
| 165 | |
| 166 | /*! Allocate a new use count entry, happens implicitly in osmo_use_count_get_put(). */ |
| 167 | static struct osmo_use_count_entry *osmo_use_count_create(struct osmo_use_count *uc, const char *use) |
| 168 | { |
| 169 | struct osmo_use_count_entry *e = talloc_zero(uc->talloc_object, struct osmo_use_count_entry); |
| 170 | if (!e) |
| 171 | return NULL; |
| 172 | *e = (struct osmo_use_count_entry){ |
| 173 | .use_count = uc, |
| 174 | .use = use, |
| 175 | }; |
| 176 | if (!uc->use_counts.next) |
| 177 | INIT_LLIST_HEAD(&uc->use_counts); |
| 178 | llist_add_tail(&e->entry, &uc->use_counts); |
| 179 | return e; |
| 180 | } |
| 181 | |
| 182 | /*! Deallocate a use count entry. |
| 183 | * Normally, this is not necessary -- it is ok and even desirable to leave use count entries around even when they reach |
| 184 | * a count of zero, until the use_count->talloc_object deallocates and removes all of them in one flush. This avoids |
| 185 | * repeated allocation and deallocation for use tokens, because use count entries that have reached zero count are |
| 186 | * repurposed for any other use tokens. A cleanup makes sense only if a very large number of differing use tokens surged |
| 187 | * at the same time, and the owning object will not be deallocated soon; if so, this should be done by the |
| 188 | * osmo_use_count_cb_t implementation. |
| 189 | * |
| 190 | * osmo_use_count_free() must *not* be called on use count entries that were added by |
| 191 | * osmo_use_count_make_static_entries(). This is the responsibility of the osmo_use_count_cb_t() implementation. |
| 192 | * |
| 193 | * \param[in] use_count_entry Use count entry to unlist and free. |
| 194 | */ |
| 195 | void osmo_use_count_free(struct osmo_use_count_entry *use_count_entry) |
| 196 | { |
| 197 | if (!use_count_entry) |
| 198 | return; |
| 199 | llist_del(&use_count_entry->entry); |
| 200 | talloc_free(use_count_entry); |
| 201 | } |
| 202 | |
| 203 | /*! Implementation for osmo_use_count_get_put(), which can also be directly invoked to pass source file information. For |
| 204 | * arguments besides file and line, see osmo_use_count_get_put(). |
| 205 | * \param[in] file Source file path, as in __FILE__. |
| 206 | * \param[in] line Source file line, as in __LINE__. |
| 207 | */ |
| 208 | int _osmo_use_count_get_put(struct osmo_use_count *uc, const char *use, int32_t change, |
| 209 | const char *file, int line) |
| 210 | { |
| 211 | struct osmo_use_count_entry *e; |
| 212 | int32_t old_use_count; |
| 213 | if (!change) |
| 214 | return 0; |
| 215 | |
| 216 | e = osmo_use_count_find(uc, use); |
| 217 | if (!e) |
| 218 | e = osmo_use_count_repurpose_zero_entry(uc, use); |
| 219 | if (!e) |
| 220 | e = osmo_use_count_create(uc, use); |
| 221 | if (!e) |
| 222 | return -ENOMEM; |
| 223 | |
| 224 | if (!e->count) { |
| 225 | /* move to end */ |
| 226 | llist_del(&e->entry); |
| 227 | llist_add_tail(&e->entry, &uc->use_counts); |
| 228 | } |
| 229 | |
| 230 | old_use_count = e->count; |
| 231 | if (!count_safe(&e->count, change)) { |
| 232 | e->count = old_use_count; |
| 233 | return -ERANGE; |
| 234 | } |
| 235 | |
| 236 | if (uc->use_cb) |
| 237 | return uc->use_cb(e, old_use_count, file, line); |
| 238 | return 0; |
| 239 | } |
| 240 | |
| 241 | /*! Add N static use token entries to avoid dynamic allocation of use count tokens. |
| 242 | * When not using this function, use count entries are talloc allocated from uc->talloc_object as talloc context. This |
| 243 | * means that there are small dynamic allocations for each use count token. osmo_use_count_get_put() normally leaves |
| 244 | * zero-count entries around and re-purposes them later, so the number of small allocations is at most the number of |
| 245 | * concurrent differently-named uses of the same object. If that is not enough, this function allows completely avoiding |
| 246 | * dynamic use count allocations, by adding N static entries with a zero count and a NULL use token. They will be used |
| 247 | * by osmo_use_count_get_put(), and, if the caller avoids using osmo_use_count_free(), the osmo_use_count implementation |
| 248 | * never deallocates them. The idea is that the entries are members of the uc->talloc_object, or that they will by other |
| 249 | * means be implicitly deallocated by the talloc_object. It is fine to call |
| 250 | * osmo_use_count_make_static_entries(buf_n_entries=N) and later have more than N concurrent uses, i.e. it is no problem |
| 251 | * to mix static and dynamic entries. To completely avoid dynamic use count entries, N has to >= the maximum number of |
| 252 | * concurrent differently-named uses that will occur in the lifetime of the talloc_object. |
| 253 | * |
| 254 | * struct my_object { |
| 255 | * struct osmo_use_count use_count; |
| 256 | * struct osmo_use_count_entry use_count_buf[3]; // planning for 3 concurrent users |
| 257 | * }; |
| 258 | * |
| 259 | * void example() { |
| 260 | * struct my_object *o = talloc_zero(ctx, struct my_object); |
| 261 | * osmo_use_count_make_static_entries(&o->use_count, o->use_count_buf, ARRAY_SIZE(o->use_count_buf)); |
| 262 | * } |
| 263 | */ |
| 264 | void osmo_use_count_make_static_entries(struct osmo_use_count *uc, struct osmo_use_count_entry *buf, |
| 265 | size_t buf_n_entries) |
| 266 | { |
| 267 | size_t idx; |
| 268 | if (!uc->use_counts.next) |
| 269 | INIT_LLIST_HEAD(&uc->use_counts); |
| 270 | for (idx = 0; idx < buf_n_entries; idx++) { |
| 271 | struct osmo_use_count_entry *e = &buf[idx]; |
| 272 | *e = (struct osmo_use_count_entry){ |
| 273 | .use_count = uc, |
| 274 | }; |
| 275 | llist_add_tail(&e->entry, &uc->use_counts); |
| 276 | } |
| 277 | } |
| 278 | |
| 279 | /*! @} */ |