lib/cmap.h

   1 /*
   2  * Copyright (c) 2014, 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
  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 /* Initializer for an empty cmap. */
  83 #define CMAP_INITIALIZER {                                              \
  84         .impl = OVSRCU_INITIALIZER((struct cmap_impl *) &empty_cmap)    \
  85     }
  86 extern OVS_ALIGNED_VAR(CACHE_LINE_SIZE) const struct cmap_impl empty_cmap;
  87
  88 /* Initialization. */
  89 void cmap_init(struct cmap *);
  90 void cmap_destroy(struct cmap *);
  91
  92 /* Count. */
  93 size_t cmap_count(const struct cmap *);
  94 bool cmap_is_empty(const struct cmap *);
  95
  96 /* Insertion and deletion.  Return the current count after the operation. */
  97 size_t cmap_insert(struct cmap *, struct cmap_node *, uint32_t hash);
  98 static inline size_t cmap_remove(struct cmap *, struct cmap_node *,
  99                                  uint32_t hash);
 100 size_t cmap_replace(struct cmap *, struct cmap_node *old_node,
 101                     struct cmap_node *new_node, uint32_t hash);
 102
 103 /* Search.
 104  *
 105  * These macros iterate NODE over all of the nodes in CMAP that have hash value
 106  * equal to HASH.  MEMBER must be the name of the 'struct cmap_node' member
 107  * within NODE.
 108  *
 109  * CMAP and HASH are evaluated only once.  NODE is evaluated many times.
 110  *
 111  *
 112  * Thread-safety
 113  * =============
 114  *
 115  * CMAP_NODE_FOR_EACH will reliably visit each of the nodes starting with
 116  * CMAP_NODE, even with concurrent insertions and deletions.  (Of
 117  * course, if nodes are being inserted or deleted, it might or might not visit
 118  * the nodes actually being inserted or deleted.)
 119  *
 120  * CMAP_NODE_FOR_EACH_PROTECTED may only be used if the containing CMAP is
 121  * guaranteed not to change during iteration.  It may be only slightly faster.
 122  *
 123  * CMAP_FOR_EACH_WITH_HASH will reliably visit each of the nodes with the
 124  * specified hash in CMAP, even with concurrent insertions and deletions.  (Of
 125  * course, if nodes with the given HASH are being inserted or deleted, it might
 126  * or might not visit the nodes actually being inserted or deleted.)
 127  *
 128  * CMAP_FOR_EACH_WITH_HASH_PROTECTED may only be used if CMAP is guaranteed not
 129  * to change during iteration.  It may be very slightly faster.
 130  */
 131 #define CMAP_NODE_FOR_EACH(NODE, MEMBER, CMAP_NODE)                     \
 132     for (INIT_CONTAINER(NODE, CMAP_NODE, MEMBER);                       \
 133          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);               \
 134          ASSIGN_CONTAINER(NODE, cmap_node_next(&(NODE)->MEMBER), MEMBER))
 135 #define CMAP_NODE_FOR_EACH_PROTECTED(NODE, MEMBER, CMAP_NODE)           \
 136     for (INIT_CONTAINER(NODE, CMAP_NODE, MEMBER);                       \
 137          (NODE) != OBJECT_CONTAINING(NULL, NODE, MEMBER);               \
 138          ASSIGN_CONTAINER(NODE, cmap_node_next_protected(&(NODE)->MEMBER), \
 139                           MEMBER))
 140 #define CMAP_FOR_EACH_WITH_HASH(NODE, MEMBER, HASH, CMAP)   \
 141     CMAP_NODE_FOR_EACH(NODE, MEMBER, cmap_find(CMAP, HASH))
 142 #define CMAP_FOR_EACH_WITH_HASH_PROTECTED(NODE, MEMBER, HASH, CMAP)     \
 143     CMAP_NODE_FOR_EACH_PROTECTED(NODE, MEMBER, cmap_find_locked(CMAP, HASH))
 144
 145 const struct cmap_node *cmap_find(const struct cmap *, uint32_t hash);
 146 struct cmap_node *cmap_find_protected(const struct cmap *, uint32_t hash);
 147
 148 /* Looks up multiple 'hashes', when the corresponding bit in 'map' is 1,
 149  * and sets the corresponding pointer in 'nodes', if the hash value was
 150  * found from the 'cmap'.  In other cases the 'nodes' values are not changed,
 151  * i.e., no NULL pointers are stored there.
 152  * Returns a map where a bit is set to 1 if the corresponding 'nodes' pointer
 153  * was stored, 0 otherwise.
 154  * Generally, the caller wants to use CMAP_NODE_FOR_EACH to verify for
 155  * hash collisions. */
 156 unsigned long cmap_find_batch(const struct cmap *cmap, unsigned long map,
 157                               uint32_t hashes[],
 158                               const struct cmap_node *nodes[]);
 159
 160 /* Iteration.
 161  *
 162  *
 163  * Thread-safety
 164  * =============
 165  *
 166  * Iteration is safe even in a cmap that is changing concurrently.  However:
 167  *
 168  *     - In the presence of concurrent calls to cmap_insert(), any given
 169  *       iteration might skip some nodes and might visit some nodes more than
 170  *       once.  If this is a problem, then the iterating code should lock the
 171  *       data structure (a rwlock can be used to allow multiple threads to
 172  *       iterate in parallel).
 173  *
 174  *     - Concurrent calls to cmap_remove() don't have the same problem.  (A
 175  *       node being deleted may be visited once or not at all.  Other nodes
 176  *       will be visited once.)
 177  *
 178  *     - If the cmap is changing, it is not safe to quiesce while iterating.
 179  *       Even if the changes are done by the same thread that's performing the
 180  *       iteration (Corollary: it is not safe to call cmap_remove() and quiesce
 181  *       in the loop body).
 182  *
 183  *
 184  * Example
 185  * =======
 186  *
 187  *     struct my_node {
 188  *         struct cmap_node cmap_node;
 189  *         int extra_data;
 190  *     };
 191  *
 192  *     struct cmap_cursor cursor;
 193  *     struct my_node *iter;
 194  *     struct cmap my_map;
 195  *
 196  *     cmap_init(&cmap);
 197  *     ...add data...
 198  *     CMAP_FOR_EACH (my_node, cmap_node, &cursor, &cmap) {
 199  *         ...operate on my_node...
 200  *     }
 201  *
 202  * CMAP_FOR_EACH is "safe" in the sense of HMAP_FOR_EACH_SAFE.  That is, it is
 203  * safe to free the current node before going on to the next iteration.  Most
 204  * of the time, though, this doesn't matter for a cmap because node
 205  * deallocation has to be postponed until the next grace period.  This means
 206  * that this guarantee is useful only in deallocation code already executing at
 207  * postponed time, when it is known that the RCU grace period has already
 208  * expired.
 209  */
 210
 211 #define CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER)    \
 212     ((CURSOR)->node                                     \
 213      ? (INIT_CONTAINER(NODE, (CURSOR)->node, MEMBER),   \
 214         cmap_cursor_advance(CURSOR),                    \
 215         true)                                           \
 216      : false)
 217
 218 #define CMAP_CURSOR_FOR_EACH(NODE, MEMBER, CURSOR, CMAP)    \
 219     for (*(CURSOR) = cmap_cursor_start(CMAP);               \
 220          CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER);      \
 221         )
 222
 223 #define CMAP_CURSOR_FOR_EACH_CONTINUE(NODE, MEMBER, CURSOR)   \
 224     while (CMAP_CURSOR_FOR_EACH__(NODE, CURSOR, MEMBER))
 225
 226 struct cmap_cursor {
 227     const struct cmap_impl *impl;
 228     uint32_t bucket_idx;
 229     int entry_idx;
 230     struct cmap_node *node;
 231 };
 232
 233 struct cmap_cursor cmap_cursor_start(const struct cmap *);
 234 void cmap_cursor_advance(struct cmap_cursor *);
 235
 236 #define CMAP_FOR_EACH(NODE, MEMBER, CMAP)                       \
 237     for (struct cmap_cursor cursor__ = cmap_cursor_start(CMAP); \
 238          CMAP_CURSOR_FOR_EACH__(NODE, &cursor__, MEMBER);       \
 239         )
 240
 241 static inline struct cmap_node *cmap_first(const struct cmap *);
 242
 243 /* Another, less preferred, form of iteration, for use in situations where it
 244  * is difficult to maintain a pointer to a cmap_node. */
 245 struct cmap_position {
 246     unsigned int bucket;
 247     unsigned int entry;
 248     unsigned int offset;
 249 };
 250
 251 struct cmap_node *cmap_next_position(const struct cmap *,
 252                                      struct cmap_position *);
 253
 254 /* Returns the first node in 'cmap', in arbitrary order, or a null pointer if
 255  * 'cmap' is empty. */
 256 static inline struct cmap_node *
 257 cmap_first(const struct cmap *cmap)
 258 {
 259     struct cmap_position pos = { 0, 0, 0 };
 260
 261     return cmap_next_position(cmap, &pos);
 262 }
 263
 264 /* Removes 'node' from 'cmap'.  The caller must ensure that 'cmap' cannot
 265  * change concurrently (from another thread).
 266  *
 267  * 'node' must not be destroyed or modified or inserted back into 'cmap' or
 268  * into any other concurrent hash map while any other thread might be accessing
 269  * it.  One correct way to do this is to free it from an RCU callback with
 270  * ovsrcu_postpone().
 271  *
 272  * Returns the current number of nodes in the cmap after the removal. */
 273 static inline size_t
 274 cmap_remove(struct cmap *cmap, struct cmap_node *node, uint32_t hash)
 275 {
 276     return cmap_replace(cmap, node, NULL, hash);
 277 }
 278
 279 #endif /* cmap.h */