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.  Return the current count after the operation. */
  91 size_t cmap_insert(struct cmap *, struct cmap_node *, uint32_t hash);
  92 static inline size_t cmap_remove(struct cmap *, struct cmap_node *,
  93                                  uint32_t hash);
  94 size_t cmap_replace(struct cmap *, struct cmap_node *old_node,
  95                     struct cmap_node *new_node, uint32_t hash);
  96
  97 /* Search.
  98  *
  99  * These macros iterate NODE over all of the nodes in CMAP that have hash value
 100  * equal to HASH.  MEMBER must be the name of the 'struct cmap_node' member
 101  * within NODE.
 102  *
 103  * CMAP and HASH are evaluated only once.  NODE is evaluated many times.
 104  *
 105  *
 106  * Thread-safety
 107  * =============
 108  *
 109  * CMAP_NODE_FOR_EACH will reliably visit each of the nodes starting with
 110  * CMAP_NODE, even with concurrent insertions and deletions.  (Of
 111  * course, if nodes are being inserted or deleted, it might or might not visit
 112  * the nodes actually being inserted or deleted.)
 113  *
 114  * CMAP_NODE_FOR_EACH_PROTECTED may only be used if the containing CMAP is
 115  * guaranteed not to change during iteration.  It may be only slightly faster.
 116  *
 117  * CMAP_FOR_EACH_WITH_HASH will reliably visit each of the nodes with the
 118  * specified hash in CMAP, even with concurrent insertions and deletions.  (Of
 119  * course, if nodes with the given HASH are being inserted or deleted, it might
 120  * or might not visit the nodes actually being inserted or deleted.)
 121  *
 122  * CMAP_FOR_EACH_WITH_HASH_PROTECTED may only be used if CMAP is guaranteed not
 123  * to change during iteration.  It may be very slightly faster.
 124  */
 125 #define CMAP_NODE_FOR_EACH(NODE, MEMBER, CMAP_NODE)                     \
 126     for (INIT_CONTAINER(NODE, CMAP_NODE, MEMBER);                       \
 127          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);               \
 128          ASSIGN_CONTAINER(NODE, cmap_node_next(&(NODE)->MEMBER), MEMBER))
 129 #define CMAP_NODE_FOR_EACH_PROTECTED(NODE, MEMBER, CMAP_NODE)           \
 130     for (INIT_CONTAINER(NODE, CMAP_NODE, MEMBER);                       \
 131          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);               \
 132          ASSIGN_CONTAINER(NODE, cmap_node_next_protected(&(NODE)->MEMBER), \
 133                           MEMBER))
 134 #define CMAP_FOR_EACH_WITH_HASH(NODE, MEMBER, HASH, CMAP)   \
 135     CMAP_NODE_FOR_EACH(NODE, MEMBER, cmap_find(CMAP, HASH))
 136 #define CMAP_FOR_EACH_WITH_HASH_PROTECTED(NODE, MEMBER, HASH, CMAP)     \
 137     CMAP_NODE_FOR_EACH_PROTECTED(NODE, MEMBER, cmap_find_locked(CMAP, HASH))
 138
 139 const struct cmap_node *cmap_find(const struct cmap *, uint32_t hash);
 140 struct cmap_node *cmap_find_protected(const struct cmap *, uint32_t hash);
 141
 142 /* Looks up multiple 'hashes', when the corresponding bit in 'map' is 1,
 143  * and sets the corresponding pointer in 'nodes', if the hash value was
 144  * found from the 'cmap'.  In other cases the 'nodes' values are not changed,
 145  * i.e., no NULL pointers are stored there.
 146  * Returns a map where a bit is set to 1 if the corresponding 'nodes' pointer
 147  * was stored, 0 otherwise.
 148  * Generally, the caller wants to use CMAP_NODE_FOR_EACH to verify for
 149  * hash collisions. */
 150 unsigned long cmap_find_batch(const struct cmap *cmap, unsigned long map,
 151                               uint32_t hashes[],
 152                               const struct cmap_node *nodes[]);
 153
 154 /* Iteration.
 155  *
 156  *
 157  * Thread-safety
 158  * =============
 159  *
 160  * Iteration is safe even in a cmap that is changing concurrently.  However:
 161  *
 162  *     - In the presence of concurrent calls to cmap_insert(), any given
 163  *       iteration might skip some nodes and might visit some nodes more than
 164  *       once.  If this is a problem, then the iterating code should lock the
 165  *       data structure (a rwlock can be used to allow multiple threads to
 166  *       iterate in parallel).
 167  *
 168  *     - Concurrent calls to cmap_remove() don't have the same problem.  (A
 169  *       node being deleted may be visited once or not at all.  Other nodes
 170  *       will be visited once.)
 171  *
 172  *
 173  * Example
 174  * =======
 175  *
 176  *     struct my_node {
 177  *         struct cmap_node cmap_node;
 178  *         int extra_data;
 179  *     };
 180  *
 181  *     struct cmap_cursor cursor;
 182  *     struct my_node *iter;
 183  *     struct cmap my_map;
 184  *
 185  *     cmap_init(&cmap);
 186  *     ...add data...
 187  *     CMAP_FOR_EACH (my_node, cmap_node, &cursor, &cmap) {
 188  *         ...operate on my_node...
 189  *     }
 190  *
 191  * CMAP_FOR_EACH is "safe" in the sense of HMAP_FOR_EACH_SAFE.  That is, it is
 192  * safe to free the current node before going on to the next iteration.  Most
 193  * of the time, though, this doesn't matter for a cmap because node
 194  * deallocation has to be postponed until the next grace period.  This means
 195  * that this guarantee is useful only in deallocation code already executing at
 196  * postponed time, when it is known that the RCU grace period has already
 197  * expired.
 198  */
 199
 200 #define CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER)    \
 201     ((CURSOR)->node                                     \
 202      ? (INIT_CONTAINER(NODE, (CURSOR)->node, MEMBER),   \
 203         cmap_cursor_advance(CURSOR),                    \
 204         true)                                           \
 205      : false)
 206
 207 #define CMAP_CURSOR_FOR_EACH(NODE, MEMBER, CURSOR, CMAP)    \
 208     for (*(CURSOR) = cmap_cursor_start(CMAP);               \
 209          CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER);      \
 210         )
 211
 212 #define CMAP_CURSOR_FOR_EACH_CONTINUE(NODE, MEMBER, CURSOR)   \
 213     while (CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER))
 214
 215 struct cmap_cursor {
 216     const struct cmap_impl *impl;
 217     uint32_t bucket_idx;
 218     int entry_idx;
 219     struct cmap_node *node;
 220 };
 221
 222 struct cmap_cursor cmap_cursor_start(const struct cmap *);
 223 void cmap_cursor_advance(struct cmap_cursor *);
 224
 225 #define CMAP_FOR_EACH(NODE, MEMBER, CMAP)                       \
 226     for (struct cmap_cursor cursor__ = cmap_cursor_start(CMAP); \
 227          CMAP_CURSOR_FOR_EACH__(NODE, &cursor__, MEMBER);       \
 228         )
 229
 230 static inline struct cmap_node *cmap_first(const struct cmap *);
 231
 232 /* Another, less preferred, form of iteration, for use in situations where it
 233  * is difficult to maintain a pointer to a cmap_node. */
 234 struct cmap_position {
 235     unsigned int bucket;
 236     unsigned int entry;
 237     unsigned int offset;
 238 };
 239
 240 struct cmap_node *cmap_next_position(const struct cmap *,
 241                                      struct cmap_position *);
 242
 243 /* Returns the first node in 'cmap', in arbitrary order, or a null pointer if
 244  * 'cmap' is empty. */
 245 static inline struct cmap_node *
 246 cmap_first(const struct cmap *cmap)
 247 {
 248     struct cmap_position pos = { 0, 0, 0 };
 249
 250     return cmap_next_position(cmap, &pos);
 251 }
 252
 253 /* Removes 'node' from 'cmap'.  The caller must ensure that 'cmap' cannot
 254  * change concurrently (from another thread).
 255  *
 256  * 'node' must not be destroyed or modified or inserted back into 'cmap' or
 257  * into any other concurrent hash map while any other thread might be accessing
 258  * it.  One correct way to do this is to free it from an RCU callback with
 259  * ovsrcu_postpone().
 260  *
 261  * Returns the current number of nodes in the cmap after the removal. */
 262 static inline size_t
 263 cmap_remove(struct cmap *cmap, struct cmap_node *node, uint32_t hash)
 264 {
 265     return cmap_replace(cmap, node, NULL, hash);
 266 }
 267
 268 #endif /* cmap.h */