lib/atomlist.h

   1 /*
   2  * Copyright (c) 2016-2019  David Lamparter, for NetDEF, Inc.
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16
  17 #ifndef _FRR_ATOMLIST_H
  18 #define _FRR_ATOMLIST_H
  19
  20 #include "typesafe.h"
  21 #include "frratomic.h"
  22
  23 #ifdef __cplusplus
  24 extern "C" {
  25 #endif
  26
  27 /* pointer with lock/deleted/invalid bit in lowest bit
  28  *
  29  * for atomlist/atomsort, "locked" means "this pointer can't be updated, the
  30  * item is being deleted".  it is permissible to assume the item will indeed
  31  * be deleted (as there are no replace/etc. ops in this).
  32  *
  33  * in general, lowest 2/3 bits on 32/64bit architectures are available for
  34  * uses like this; the only thing that will really break this is putting an
  35  * atomlist_item in a struct with "packed" attribute.  (it'll break
  36  * immediately and consistently.) -- don't do that.
  37  *
  38  * ATOMPTR_USER is currently unused (and available for atomic hash or skiplist
  39  * implementations.)
  40  */
  41
  42 /* atomic_atomptr_t may look a bit odd, it's for the sake of C++ compat */
  43 typedef uintptr_t               atomptr_t;
  44 typedef atomic_uintptr_t        atomic_atomptr_t;
  45
  46 #define ATOMPTR_MASK (UINTPTR_MAX - 3)
  47 #define ATOMPTR_LOCK (1)
  48 #define ATOMPTR_USER (2)
  49 #define ATOMPTR_NULL (0)
  50
  51 static inline atomptr_t atomptr_i(void *val)
  52 {
  53         atomptr_t atomval = (atomptr_t)val;
  54
  55         assert(!(atomval & ATOMPTR_LOCK));
  56         return atomval;
  57 }
  58 static inline void *atomptr_p(atomptr_t val)
  59 {
  60         return (void *)(val & ATOMPTR_MASK);
  61 }
  62 static inline bool atomptr_l(atomptr_t val)
  63 {
  64         return (bool)(val & ATOMPTR_LOCK);
  65 }
  66 static inline bool atomptr_u(atomptr_t val)
  67 {
  68         return (bool)(val & ATOMPTR_USER);
  69 }
  70
  71
  72 /* the problem with, find(), find_gteq() and find_lt() on atomic lists is that
  73  * they're neither an "acquire" nor a "release" operation;  the element that
  74  * was found is still on the list and doesn't change ownership.  Therefore,
  75  * an atomic transition in ownership state can't be implemented.
  76  *
  77  * Contrast this with add() or pop(): both function calls atomically transfer
  78  * ownership of an item to or from the list, which makes them "acquire" /
  79  * "release" operations.
  80  *
  81  * What can be implemented atomically is a "find_pop()", i.e. try to locate an
  82  * item and atomically try to remove it if found.  It's not currently
  83  * implemented but can be added when needed.
  84  *
  85  * Either way - for find(), generally speaking, if you need to use find() on
  86  * a list then the whole thing probably isn't well-suited to atomic
  87  * implementation and you'll need to have extra locks around to make it work
  88  * correctly.
  89  */
  90 #ifdef WNO_ATOMLIST_UNSAFE_FIND
  91 # define atomic_find_warn
  92 #else
  93 # define atomic_find_warn __attribute__((_DEPRECATED( \
  94         "WARNING: find() on atomic lists cannot be atomic by principle; " \
  95         "check code to make sure usage pattern is OK and if it is, use " \
  96         "#define WNO_ATOMLIST_UNSAFE_FIND")))
  97 #endif
  98
  99
 100 /* single-linked list, unsorted/arbitrary.
 101  * can be used as queue with add_tail / pop
 102  *
 103  * all operations are lock-free, but not neccessarily wait-free.  this means
 104  * that there is no state where the system as a whole stops making process,
 105  * but it *is* possible that a *particular* thread is delayed by some time.
 106  *
 107  * the only way for this to happen is for other threads to continuously make
 108  * updates.  an inactive / blocked / deadlocked other thread cannot cause such
 109  * delays, and to cause such delays a thread must be heavily hitting the list -
 110  * it's a rather theoretical concern.
 111  */
 112
 113 /* don't use these structs directly */
 114 struct atomlist_item {
 115         atomic_uintptr_t next;
 116 };
 117 #define atomlist_itemp(val) ((struct atomlist_item *)atomptr_p(val))
 118
 119 struct atomlist_head {
 120         atomic_uintptr_t first, last;
 121         atomic_size_t count;
 122 };
 123
 124 /* use as:
 125  *
 126  * PREDECL_ATOMLIST(namelist)
 127  * struct name {
 128  *   struct namelist_item nlitem;
 129  * }
 130  * DECLARE_ATOMLIST(namelist, struct name, nlitem)
 131  */
 132 #define PREDECL_ATOMLIST(prefix)                                               \
 133 struct prefix ## _head { struct atomlist_head ah; };                           \
 134 struct prefix ## _item { struct atomlist_item ai; };
 135
 136 #define INIT_ATOMLIST(var) { }
 137
 138 #define DECLARE_ATOMLIST(prefix, type, field)                                  \
 139 macro_inline void prefix ## _add_head(struct prefix##_head *h, type *item)     \
 140 {       atomlist_add_head(&h->ah, &item->field.ai); }                          \
 141 macro_inline void prefix ## _add_tail(struct prefix##_head *h, type *item)     \
 142 {       atomlist_add_tail(&h->ah, &item->field.ai); }                          \
 143 macro_inline void prefix ## _del_hint(struct prefix##_head *h, type *item,     \
 144                 atomic_atomptr_t *hint)                                        \
 145 {       atomlist_del_hint(&h->ah, &item->field.ai, hint); }                    \
 146 macro_inline type *prefix ## _del(struct prefix##_head *h, type *item)         \
 147 {       atomlist_del_hint(&h->ah, &item->field.ai, NULL);                      \
 148         /* TODO: Return NULL if not found */                                   \
 149         return item; }                                                         \
 150 macro_inline type *prefix ## _pop(struct prefix##_head *h)                     \
 151 {       char *p = (char *)atomlist_pop(&h->ah);                                \
 152         return p ? (type *)(p - offsetof(type, field)) : NULL; }               \
 153 macro_inline type *prefix ## _first(struct prefix##_head *h)                   \
 154 {       char *p = atomptr_p(atomic_load_explicit(&h->ah.first,                 \
 155                                 memory_order_acquire));                        \
 156         return p ? (type *)(p - offsetof(type, field)) : NULL; }               \
 157 macro_inline type *prefix ## _next(struct prefix##_head *h, type *item)        \
 158 {       char *p = atomptr_p(atomic_load_explicit(&item->field.ai.next,         \
 159                                 memory_order_acquire));                        \
 160         return p ? (type *)(p - offsetof(type, field)) : NULL; }               \
 161 macro_inline type *prefix ## _next_safe(struct prefix##_head *h, type *item)   \
 162 {       return item ? prefix##_next(h, item) : NULL; }                         \
 163 macro_inline size_t prefix ## _count(struct prefix##_head *h)                  \
 164 {       return atomic_load_explicit(&h->ah.count, memory_order_relaxed); }     \
 165 macro_inline void prefix ## _init(struct prefix##_head *h)                     \
 166 {                                                                              \
 167         memset(h, 0, sizeof(*h));                                              \
 168 }                                                                              \
 169 macro_inline void prefix ## _fini(struct prefix##_head *h)                     \
 170 {                                                                              \
 171         assert(prefix ## _count(h) == 0);                                      \
 172         memset(h, 0, sizeof(*h));                                              \
 173 }                                                                              \
 174 /* ... */
 175
 176 /* add_head:
 177  * - contention on ->first pointer
 178  * - return implies completion
 179  */
 180 void atomlist_add_head(struct atomlist_head *h, struct atomlist_item *item);
 181
 182 /* add_tail:
 183  * - concurrent add_tail can cause wait but has progress guarantee
 184  * - return does NOT imply completion.  completion is only guaranteed after
 185  *   all other add_tail operations that started before this add_tail have
 186  *   completed as well.
 187  */
 188 void atomlist_add_tail(struct atomlist_head *h, struct atomlist_item *item);
 189
 190 /* del/del_hint:
 191  *
 192  * OWNER MUST HOLD REFERENCE ON ITEM TO BE DELETED, ENSURING NO OTHER THREAD
 193  * WILL TRY TO DELETE THE SAME ITEM.  DELETING INCLUDES pop().
 194  *
 195  * as with all deletions, threads that started reading earlier may still hold
 196  * pointers to the deleted item.  completion is however guaranteed for all
 197  * reads starting later.
 198  */
 199 void atomlist_del_hint(struct atomlist_head *h, struct atomlist_item *item,
 200                 atomic_atomptr_t *hint);
 201
 202 /* pop:
 203  *
 204  * as with all deletions, threads that started reading earlier may still hold
 205  * pointers to the deleted item.  completion is however guaranteed for all
 206  * reads starting later.
 207  */
 208 struct atomlist_item *atomlist_pop(struct atomlist_head *h);
 209
 210
 211
 212 struct atomsort_item {
 213         atomic_atomptr_t next;
 214 };
 215 #define atomsort_itemp(val) ((struct atomsort_item *)atomptr_p(val))
 216
 217 struct atomsort_head {
 218         atomic_atomptr_t first;
 219         atomic_size_t count;
 220 };
 221
 222 #define _PREDECL_ATOMSORT(prefix)                                              \
 223 struct prefix ## _head { struct atomsort_head ah; };                           \
 224 struct prefix ## _item { struct atomsort_item ai; };
 225
 226 #define INIT_ATOMSORT_UNIQ(var)         { }
 227 #define INIT_ATOMSORT_NONUNIQ(var)      { }
 228
 229 #define _DECLARE_ATOMSORT(prefix, type, field, cmpfn_nuq, cmpfn_uq)            \
 230 macro_inline void prefix ## _init(struct prefix##_head *h)                     \
 231 {                                                                              \
 232         memset(h, 0, sizeof(*h));                                              \
 233 }                                                                              \
 234 macro_inline void prefix ## _fini(struct prefix##_head *h)                     \
 235 {                                                                              \
 236         assert(h->ah.count == 0);                                              \
 237         memset(h, 0, sizeof(*h));                                              \
 238 }                                                                              \
 239 macro_inline type *prefix ## _add(struct prefix##_head *h, type *item)         \
 240 {                                                                              \
 241         struct atomsort_item *p;                                               \
 242         p = atomsort_add(&h->ah, &item->field.ai, cmpfn_uq);                   \
 243         return container_of_null(p, type, field.ai);                           \
 244 }                                                                              \
 245 macro_inline type *prefix ## _first(struct prefix##_head *h)                   \
 246 {                                                                              \
 247         struct atomsort_item *p;                                               \
 248         p = atomptr_p(atomic_load_explicit(&h->ah.first,                       \
 249                                 memory_order_acquire));                        \
 250         return container_of_null(p, type, field.ai);                           \
 251 }                                                                              \
 252 macro_inline type *prefix ## _next(struct prefix##_head *h, type *item)        \
 253 {                                                                              \
 254         struct atomsort_item *p;                                               \
 255         p = atomptr_p(atomic_load_explicit(&item->field.ai.next,               \
 256                                 memory_order_acquire));                        \
 257         return container_of_null(p, type, field.ai);                           \
 258 }                                                                              \
 259 macro_inline type *prefix ## _next_safe(struct prefix##_head *h, type *item)   \
 260 {                                                                              \
 261         return item ? prefix##_next(h, item) : NULL;                           \
 262 }                                                                              \
 263 atomic_find_warn                                                               \
 264 macro_inline type *prefix ## _find_gteq(struct prefix##_head *h,               \
 265                 const type *item)                                              \
 266 {                                                                              \
 267         type *p = prefix ## _first(h);                                         \
 268         while (p && cmpfn_nuq(&p->field.ai, &item->field.ai) < 0)              \
 269                 p = prefix ## _next(h, p);                                     \
 270         return p;                                                              \
 271 }                                                                              \
 272 atomic_find_warn                                                               \
 273 macro_inline type *prefix ## _find_lt(struct prefix##_head *h,                 \
 274                 const type *item)                                              \
 275 {                                                                              \
 276         type *p = prefix ## _first(h), *prev = NULL;                           \
 277         while (p && cmpfn_nuq(&p->field.ai, &item->field.ai) < 0)              \
 278                 p = prefix ## _next(h, (prev = p));                            \
 279         return prev;                                                           \
 280 }                                                                              \
 281 macro_inline void prefix ## _del_hint(struct prefix##_head *h, type *item,     \
 282                 atomic_atomptr_t *hint)                                        \
 283 {                                                                              \
 284         atomsort_del_hint(&h->ah, &item->field.ai, hint);                      \
 285 }                                                                              \
 286 macro_inline type *prefix ## _del(struct prefix##_head *h, type *item)         \
 287 {                                                                              \
 288         atomsort_del_hint(&h->ah, &item->field.ai, NULL);                      \
 289         /* TODO: Return NULL if not found */                                   \
 290         return item;                                                           \
 291 }                                                                              \
 292 macro_inline size_t prefix ## _count(struct prefix##_head *h)                  \
 293 {                                                                              \
 294         return atomic_load_explicit(&h->ah.count, memory_order_relaxed);       \
 295 }                                                                              \
 296 macro_inline type *prefix ## _pop(struct prefix##_head *h)                     \
 297 {                                                                              \
 298         struct atomsort_item *p = atomsort_pop(&h->ah);                        \
 299         return p ? container_of(p, type, field.ai) : NULL;                     \
 300 }                                                                              \
 301 /* ... */
 302
 303 #define PREDECL_ATOMSORT_UNIQ(prefix)                                          \
 304         _PREDECL_ATOMSORT(prefix)
 305 #define DECLARE_ATOMSORT_UNIQ(prefix, type, field, cmpfn)                      \
 306                                                                                \
 307 macro_inline int prefix ## __cmp(const struct atomsort_item *a,                \
 308                 const struct atomsort_item *b)                                 \
 309 {                                                                              \
 310         return cmpfn(container_of(a, type, field.ai),                          \
 311                         container_of(b, type, field.ai));                      \
 312 }                                                                              \
 313                                                                                \
 314 _DECLARE_ATOMSORT(prefix, type, field,                                         \
 315                 prefix ## __cmp, prefix ## __cmp)                              \
 316                                                                                \
 317 atomic_find_warn                                                               \
 318 macro_inline type *prefix ## _find(struct prefix##_head *h, const type *item)  \
 319 {                                                                              \
 320         type *p = prefix ## _first(h);                                         \
 321         int cmpval = 0;                                                        \
 322         while (p && (cmpval = cmpfn(p, item)) < 0)                             \
 323                 p = prefix ## _next(h, p);                                     \
 324         if (!p || cmpval > 0)                                                  \
 325                 return NULL;                                                   \
 326         return p;                                                              \
 327 }                                                                              \
 328 /* ... */
 329
 330 #define PREDECL_ATOMSORT_NONUNIQ(prefix)                                       \
 331         _PREDECL_ATOMSORT(prefix)
 332 #define DECLARE_ATOMSORT_NONUNIQ(prefix, type, field, cmpfn)                   \
 333                                                                                \
 334 macro_inline int prefix ## __cmp(const struct atomsort_item *a,                \
 335                 const struct atomsort_item *b)                                 \
 336 {                                                                              \
 337         return cmpfn(container_of(a, type, field.ai),                          \
 338                         container_of(b, type, field.ai));                      \
 339 }                                                                              \
 340 macro_inline int prefix ## __cmp_uq(const struct atomsort_item *a,             \
 341                 const struct atomsort_item *b)                                 \
 342 {                                                                              \
 343         int cmpval = cmpfn(container_of(a, type, field.ai),                    \
 344                         container_of(b, type, field.ai));                      \
 345         if (cmpval)                                                            \
 346                 return cmpval;                                                 \
 347         if (a < b)                                                             \
 348                 return -1;                                                     \
 349         if (a > b)                                                             \
 350                 return 1;                                                      \
 351         return 0;                                                              \
 352 }                                                                              \
 353                                                                                \
 354 _DECLARE_ATOMSORT(prefix, type, field,                                         \
 355                 prefix ## __cmp, prefix ## __cmp_uq)                           \
 356 /* ... */
 357
 358 struct atomsort_item *atomsort_add(struct atomsort_head *h,
 359                 struct atomsort_item *item, int (*cmpfn)(
 360                         const struct atomsort_item *,
 361                         const struct atomsort_item *));
 362
 363 void atomsort_del_hint(struct atomsort_head *h,
 364                 struct atomsort_item *item, atomic_atomptr_t *hint);
 365
 366 struct atomsort_item *atomsort_pop(struct atomsort_head *h);
 367
 368 #ifdef __cplusplus
 369 }
 370 #endif
 371
 372 #endif /* _FRR_ATOMLIST_H */