lib/list.h

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2013, 2015, 2016 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #ifndef LIST_H
  17 #define LIST_H 1
  18
  19 /* Doubly linked list. */
  20
  21 #include <stdbool.h>
  22 #include <stddef.h>
  23 #include "util.h"
  24 #include "openvswitch/list.h"
  25
  26 /* "struct ovs_list" with pointers that will (probably) cause segfaults if
  27  * dereferenced and, better yet, show up clearly in a debugger.
  28
  29  * MSVC2015 doesn't support designated initializers when compiling C++,
  30  * and doesn't support ternary operators with non-designated initializers.
  31  * So we use these static definitions rather than using initializer macros. */
  32 static const struct ovs_list OVS_LIST_POISON =
  33     { (struct ovs_list *) (UINTPTR_MAX / 0xf * 0xc),
  34       (struct ovs_list *) (UINTPTR_MAX / 0xf * 0xc) };
  35
  36 static inline void list_init(struct ovs_list *);
  37 static inline void list_poison(struct ovs_list *);
  38
  39 /* List insertion. */
  40 static inline void list_insert(struct ovs_list *, struct ovs_list *);
  41 static inline void list_splice(struct ovs_list *before, struct ovs_list *first,
  42                                struct ovs_list *last);
  43 static inline void list_push_front(struct ovs_list *, struct ovs_list *);
  44 static inline void list_push_back(struct ovs_list *, struct ovs_list *);
  45 static inline void list_replace(struct ovs_list *, const struct ovs_list *);
  46 static inline void list_moved(struct ovs_list *, const struct ovs_list *orig);
  47 static inline void list_move(struct ovs_list *dst, struct ovs_list *src);
  48
  49 /* List removal. */
  50 static inline struct ovs_list *list_remove(struct ovs_list *);
  51 static inline struct ovs_list *list_pop_front(struct ovs_list *);
  52 static inline struct ovs_list *list_pop_back(struct ovs_list *);
  53
  54 /* List elements. */
  55 static inline struct ovs_list *list_front(const struct ovs_list *);
  56 static inline struct ovs_list *list_back(const struct ovs_list *);
  57
  58 /* List properties. */
  59 static inline size_t list_size(const struct ovs_list *);
  60 static inline bool list_is_empty(const struct ovs_list *);
  61 static inline bool list_is_singleton(const struct ovs_list *);
  62 static inline bool list_is_short(const struct ovs_list *);
  63
  64 #define LIST_FOR_EACH(ITER, MEMBER, LIST)                               \
  65     for (INIT_CONTAINER(ITER, (LIST)->next, MEMBER);                    \
  66          &(ITER)->MEMBER != (LIST);                                     \
  67          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER))
  68 #define LIST_FOR_EACH_CONTINUE(ITER, MEMBER, LIST)                      \
  69     for (ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER);             \
  70          &(ITER)->MEMBER != (LIST);                                     \
  71          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.next, MEMBER))
  72 #define LIST_FOR_EACH_REVERSE(ITER, MEMBER, LIST)                       \
  73     for (INIT_CONTAINER(ITER, (LIST)->prev, MEMBER);                    \
  74          &(ITER)->MEMBER != (LIST);                                     \
  75          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
  76 #define LIST_FOR_EACH_REVERSE_CONTINUE(ITER, MEMBER, LIST)              \
  77     for (ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER);           \
  78          &(ITER)->MEMBER != (LIST);                                     \
  79          ASSIGN_CONTAINER(ITER, (ITER)->MEMBER.prev, MEMBER))
  80 #define LIST_FOR_EACH_SAFE(ITER, NEXT, MEMBER, LIST)               \
  81     for (INIT_CONTAINER(ITER, (LIST)->next, MEMBER);               \
  82          (&(ITER)->MEMBER != (LIST)                                \
  83           ? INIT_CONTAINER(NEXT, (ITER)->MEMBER.next, MEMBER), 1   \
  84           : 0);                                                    \
  85          (ITER) = (NEXT))
  86 #define LIST_FOR_EACH_POP(ITER, MEMBER, LIST)                      \
  87     while (!list_is_empty(LIST)                                    \
  88            && (INIT_CONTAINER(ITER, list_pop_front(LIST), MEMBER), 1))
  89 \f
  90 /* Inline implementations. */
  91
  92 /* Initializes 'list' as an empty list. */
  93 static inline void
  94 list_init(struct ovs_list *list)
  95 {
  96     list->next = list->prev = list;
  97 }
  98
  99 /* Initializes 'list' with pointers that will (probably) cause segfaults if
 100  * dereferenced and, better yet, show up clearly in a debugger. */
 101 static inline void
 102 list_poison(struct ovs_list *list)
 103 {
 104     *list = OVS_LIST_POISON;
 105 }
 106
 107 /* Inserts 'elem' just before 'before'. */
 108 static inline void
 109 list_insert(struct ovs_list *before, struct ovs_list *elem)
 110 {
 111     elem->prev = before->prev;
 112     elem->next = before;
 113     before->prev->next = elem;
 114     before->prev = elem;
 115 }
 116
 117 /* Removes elements 'first' though 'last' (exclusive) from their current list,
 118    then inserts them just before 'before'. */
 119 static inline void
 120 list_splice(struct ovs_list *before, struct ovs_list *first, struct ovs_list *last)
 121 {
 122     if (first == last) {
 123         return;
 124     }
 125     last = last->prev;
 126
 127     /* Cleanly remove 'first'...'last' from its current list. */
 128     first->prev->next = last->next;
 129     last->next->prev = first->prev;
 130
 131     /* Splice 'first'...'last' into new list. */
 132     first->prev = before->prev;
 133     last->next = before;
 134     before->prev->next = first;
 135     before->prev = last;
 136 }
 137
 138 /* Inserts 'elem' at the beginning of 'list', so that it becomes the front in
 139    'list'. */
 140 static inline void
 141 list_push_front(struct ovs_list *list, struct ovs_list *elem)
 142 {
 143     list_insert(list->next, elem);
 144 }
 145
 146 /* Inserts 'elem' at the end of 'list', so that it becomes the back in
 147  * 'list'. */
 148 static inline void
 149 list_push_back(struct ovs_list *list, struct ovs_list *elem)
 150 {
 151     list_insert(list, elem);
 152 }
 153
 154 /* Puts 'elem' in the position currently occupied by 'position'.
 155  * Afterward, 'position' is not part of a list. */
 156 static inline void
 157 list_replace(struct ovs_list *element, const struct ovs_list *position)
 158 {
 159     element->next = position->next;
 160     element->next->prev = element;
 161     element->prev = position->prev;
 162     element->prev->next = element;
 163 }
 164
 165 /* Adjusts pointers around 'list' to compensate for 'list' having been moved
 166  * around in memory (e.g. as a consequence of realloc()), with original
 167  * location 'orig'.
 168  *
 169  * ('orig' likely points to freed memory, but this function does not
 170  * dereference 'orig', it only compares it to 'list'.  In a very pedantic
 171  * language lawyer sense, this still yields undefined behavior, but it works
 172  * with actual compilers.) */
 173 static inline void
 174 list_moved(struct ovs_list *list, const struct ovs_list *orig)
 175 {
 176     if (list->next == orig) {
 177         list_init(list);
 178     } else {
 179         list->prev->next = list->next->prev = list;
 180     }
 181 }
 182
 183 /* Initializes 'dst' with the contents of 'src', compensating for moving it
 184  * around in memory.  The effect is that, if 'src' was the head of a list, now
 185  * 'dst' is the head of a list containing the same elements. */
 186 static inline void
 187 list_move(struct ovs_list *dst, struct ovs_list *src)
 188 {
 189     *dst = *src;
 190     list_moved(dst, src);
 191 }
 192
 193 /* Removes 'elem' from its list and returns the element that followed it.
 194    Undefined behavior if 'elem' is not in a list. */
 195 static inline struct ovs_list *
 196 list_remove(struct ovs_list *elem)
 197 {
 198     elem->prev->next = elem->next;
 199     elem->next->prev = elem->prev;
 200     return elem->next;
 201 }
 202
 203 /* Removes the front element from 'list' and returns it.  Undefined behavior if
 204    'list' is empty before removal. */
 205 static inline struct ovs_list *
 206 list_pop_front(struct ovs_list *list)
 207 {
 208     struct ovs_list *front = list->next;
 209
 210     list_remove(front);
 211     return front;
 212 }
 213
 214 /* Removes the back element from 'list' and returns it.
 215    Undefined behavior if 'list' is empty before removal. */
 216 static inline struct ovs_list *
 217 list_pop_back(struct ovs_list *list)
 218 {
 219     struct ovs_list *back = list->prev;
 220
 221     list_remove(back);
 222     return back;
 223 }
 224
 225 /* Returns the front element in 'list_'.
 226    Undefined behavior if 'list_' is empty. */
 227 static inline struct ovs_list *
 228 list_front(const struct ovs_list *list_)
 229 {
 230     struct ovs_list *list = CONST_CAST(struct ovs_list *, list_);
 231
 232     ovs_assert(!list_is_empty(list));
 233
 234     return list->next;
 235 }
 236
 237 /* Returns the back element in 'list_'.
 238    Undefined behavior if 'list_' is empty. */
 239 static inline struct ovs_list *
 240 list_back(const struct ovs_list *list_)
 241 {
 242     struct ovs_list *list = CONST_CAST(struct ovs_list *, list_);
 243
 244     ovs_assert(!list_is_empty(list));
 245
 246     return list->prev;
 247 }
 248
 249 /* Returns the number of elements in 'list'.
 250    Runs in O(n) in the number of elements. */
 251 static inline size_t
 252 list_size(const struct ovs_list *list)
 253 {
 254     const struct ovs_list *e;
 255     size_t cnt = 0;
 256
 257     for (e = list->next; e != list; e = e->next) {
 258         cnt++;
 259     }
 260     return cnt;
 261 }
 262
 263 /* Returns true if 'list' is empty, false otherwise. */
 264 static inline bool
 265 list_is_empty(const struct ovs_list *list)
 266 {
 267     return list->next == list;
 268 }
 269
 270 /* Returns true if 'list' has exactly 1 element, false otherwise. */
 271 static inline bool
 272 list_is_singleton(const struct ovs_list *list)
 273 {
 274     return list_is_short(list) && !list_is_empty(list);
 275 }
 276
 277 /* Returns true if 'list' has 0 or 1 elements, false otherwise. */
 278 static inline bool
 279 list_is_short(const struct ovs_list *list)
 280 {
 281     return list->next == list->prev;
 282 }
 283
 284 #endif /* list.h */