lib/cmap.h

   1 /*
   2  * Copyright (c) 2014 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
  17 #ifndef CMAP_H
  18 #define CMAP_H 1
  19
  20 #include <stdbool.h>
  21 #include <stdint.h>
  22 #include "ovs-rcu.h"
  23 #include "util.h"
  24
  25 /* Concurrent hash map
  26  * ===================
  27  *
  28  * A single-writer, multiple-reader hash table that efficiently supports
  29  * duplicates.
  30  *
  31  *
  32  * Thread-safety
  33  * =============
  34  *
  35  * The general rules are:
  36  *
  37  *    - Only a single thread may safely call into cmap_insert(),
  38  *      cmap_remove(), or cmap_replace() at any given time.
  39  *
  40  *    - Any number of threads may use functions and macros that search or
  41  *      iterate through a given cmap, even in parallel with other threads
  42  *      calling cmap_insert(), cmap_remove(), or cmap_replace().
  43  *
  44  *      There is one exception: cmap_find_protected() is only safe if no thread
  45  *      is currently calling cmap_insert(), cmap_remove(), or cmap_replace().
  46  *      (Use ordinary cmap_find() if that is not guaranteed.)
  47  *
  48  *    - See "Iteration" below for additional thread safety rules.
  49  *
  50  * Writers must use special care to ensure that any elements that they remove
  51  * do not get freed or reused until readers have finished with them.  This
  52  * includes inserting the element back into its original cmap or a different
  53  * one.  One correct way to do this is to free them from an RCU callback with
  54  * ovsrcu_postpone().
  55  */
  56
  57 /* A concurrent hash map node, to be embedded inside the data structure being
  58  * mapped.
  59  *
  60  * All nodes linked together on a chain have exactly the same hash value. */
  61 struct cmap_node {
  62     OVSRCU_TYPE(struct cmap_node *) next; /* Next node with same hash. */
  63 };
  64
  65 static inline struct cmap_node *
  66 cmap_node_next(const struct cmap_node *node)
  67 {
  68     return ovsrcu_get(struct cmap_node *, &node->next);
  69 }
  70
  71 static inline struct cmap_node *
  72 cmap_node_next_protected(const struct cmap_node *node)
  73 {
  74     return ovsrcu_get_protected(struct cmap_node *, &node->next);
  75 }
  76
  77 /* Concurrent hash map. */
  78 struct cmap {
  79     OVSRCU_TYPE(struct cmap_impl *) impl;
  80 };
  81
  82 /* Initialization. */
  83 void cmap_init(struct cmap *);
  84 void cmap_destroy(struct cmap *);
  85
  86 /* Count. */
  87 size_t cmap_count(const struct cmap *);
  88 bool cmap_is_empty(const struct cmap *);
  89
  90 /* Insertion and deletion. */
  91 void cmap_insert(struct cmap *, struct cmap_node *, uint32_t hash);
  92 void cmap_remove(struct cmap *, struct cmap_node *, uint32_t hash);
  93 void cmap_replace(struct cmap *, struct cmap_node *old_node,
  94                   struct cmap_node *new_node, uint32_t hash);
  95
  96 /* Search.
  97  *
  98  * These macros iterate NODE over all of the nodes in CMAP that have hash value
  99  * equal to HASH.  MEMBER must be the name of the 'struct cmap_node' member
 100  * within NODE.
 101  *
 102  * CMAP and HASH are evaluated only once.  NODE is evaluated many times.
 103  *
 104  *
 105  * Thread-safety
 106  * =============
 107  *
 108  * CMAP_FOR_EACH_WITH_HASH will reliably visit each of the nodes with the
 109  * specified hash in CMAP, even with concurrent insertions and deletions.  (Of
 110  * course, if nodes with the given HASH are being inserted or deleted, it might
 111  * or might not visit the nodes actually being inserted or deleted.)
 112  *
 113  * CMAP_FOR_EACH_WITH_HASH_PROTECTED may only be used if CMAP is guaranteed not
 114  * to change during iteration.  It may be very slightly faster.
 115  */
 116 #define CMAP_FOR_EACH_WITH_HASH(NODE, MEMBER, HASH, CMAP)       \
 117     for (ASSIGN_CONTAINER(NODE, cmap_find(CMAP, HASH), MEMBER); \
 118          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);       \
 119          ASSIGN_CONTAINER(NODE, cmap_node_next(&(NODE)->MEMBER), MEMBER))
 120 #define CMAP_FOR_EACH_WITH_HASH_PROTECTED(NODE, MEMBER, HASH, CMAP)        \
 121     for (ASSIGN_CONTAINER(NODE, cmap_find_locked(CMAP, HASH), MEMBER);  \
 122          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);               \
 123          ASSIGN_CONTAINER(NODE, cmap_node_next_protected(&(NODE)->MEMBER), \
 124                           MEMBER))
 125
 126 struct cmap_node *cmap_find(const struct cmap *, uint32_t hash);
 127 struct cmap_node *cmap_find_protected(const struct cmap *, uint32_t hash);
 128
 129 /* Iteration.
 130  *
 131  *
 132  * Thread-safety
 133  * =============
 134  *
 135  * Iteration is safe even in a cmap that is changing concurrently.  However:
 136  *
 137  *     - In the presence of concurrent calls to cmap_insert(), any given
 138  *       iteration might skip some nodes and might visit some nodes more than
 139  *       once.  If this is a problem, then the iterating code should lock the
 140  *       data structure (a rwlock can be used to allow multiple threads to
 141  *       iterate in parallel).
 142  *
 143  *     - Concurrent calls to cmap_remove() don't have the same problem.  (A
 144  *       node being deleted may be visited once or not at all.  Other nodes
 145  *       will be visited once.)
 146  *
 147  *
 148  * Example
 149  * =======
 150  *
 151  *     struct my_node {
 152  *         struct cmap_node cmap_node;
 153  *         int extra_data;
 154  *     };
 155  *
 156  *     struct cmap_cursor cursor;
 157  *     struct my_node *iter;
 158  *     struct cmap my_map;
 159  *
 160  *     cmap_init(&cmap);
 161  *     ...add data...
 162  *     CMAP_FOR_EACH (my_node, cmap_node, &cursor, &cmap) {
 163  *         ...operate on my_node...
 164  *     }
 165  *
 166  * CMAP_FOR_EACH is "safe" in the sense of HMAP_FOR_EACH_SAFE.  That is, it is
 167  * safe to free the current node before going on to the next iteration.  Most
 168  * of the time, though, this doesn't matter for a cmap because node
 169  * deallocation has to be postponed until the next grace period.  This means
 170  * that this guarantee is useful only in deallocation code already executing at
 171  * postponed time, when it is known that the RCU grace period has already
 172  * expired.
 173  */
 174
 175 #define CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER)    \
 176     ((CURSOR)->node                                     \
 177      ? (ASSIGN_CONTAINER(NODE, (CURSOR)->node, MEMBER), \
 178         cmap_cursor_advance(CURSOR),                    \
 179         true)                                           \
 180      : false)
 181
 182 #define CMAP_CURSOR_FOR_EACH(NODE, MEMBER, CURSOR, CMAP)    \
 183     for (*(CURSOR) = cmap_cursor_start(CMAP);               \
 184          CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER);      \
 185         )
 186
 187 #define CMAP_CURSOR_FOR_EACH_CONTINUE(NODE, MEMBER, CURSOR)   \
 188     while (CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER))
 189
 190 struct cmap_cursor {
 191     const struct cmap_impl *impl;
 192     uint32_t bucket_idx;
 193     int entry_idx;
 194     struct cmap_node *node;
 195 };
 196
 197 struct cmap_cursor cmap_cursor_start(const struct cmap *);
 198 void cmap_cursor_advance(struct cmap_cursor *);
 199
 200 #define CMAP_FOR_EACH(NODE, MEMBER, CMAP)                       \
 201     for (struct cmap_cursor cursor__ = cmap_cursor_start(CMAP); \
 202          CMAP_CURSOR_FOR_EACH__(NODE, &cursor__, MEMBER);       \
 203         )
 204
 205 static inline struct cmap_node *cmap_first(const struct cmap *);
 206
 207 /* Another, less preferred, form of iteration, for use in situations where it
 208  * is difficult to maintain a pointer to a cmap_node. */
 209 struct cmap_position {
 210     unsigned int bucket;
 211     unsigned int entry;
 212     unsigned int offset;
 213 };
 214
 215 struct cmap_node *cmap_next_position(const struct cmap *,
 216                                      struct cmap_position *);
 217
 218 /* Returns the first node in 'cmap', in arbitrary order, or a null pointer if
 219  * 'cmap' is empty. */
 220 static inline struct cmap_node *
 221 cmap_first(const struct cmap *cmap)
 222 {
 223     struct cmap_position pos = { 0, 0, 0 };
 224
 225     return cmap_next_position(cmap, &pos);
 226 }
 227
 228 #endif /* cmap.h */