lib/pvector.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 PVECTOR_H
  18 #define PVECTOR_H 1
  19
  20 #include <stdbool.h>
  21 #include <stdint.h>
  22 #include <stdlib.h>
  23 #include "ovs-rcu.h"
  24 #include "util.h"
  25
  26 /* Concurrent Priority Vector
  27  * ==========================
  28  *
  29  * Concurrent priority vector holds non-NULL pointers to objects in an
  30  * increasing priority order and allows readers to traverse the vector without
  31  * being concerned about writers modifying the vector as they are traversing
  32  * it.
  33  *
  34  * The priority order is maintained as a linear vector of elements to allow
  35  * for efficient memory prefetching.
  36  *
  37  * Concurrency is implemented with OVS RCU so that the readers can assume
  38  * that once they have taken a pointer to the vector with
  39  * pvector_cursor_init(), the 'size' member will not decrease, so that
  40  * they can safely read 'size' entries from 'vector', and find that each
  41  * entry has a valid, non-NULL 'ptr', and the vector is in order from highest
  42  * to lowest 'priority'.  The 'priority' values can change any time, but only
  43  * so that the order of the entries does not change, so readers can use
  44  * 'priority' values read at any time after acquisition of the vector pointer.
  45  *
  46  * Writers can concurrently add entries to the end of the vector, incrementing
  47  * 'size', or update the 'priority' value of an entry, but only if that does
  48  * not change the ordering of the entries.  Writers will never change the 'ptr'
  49  * values, or decrement the 'size' on a copy that readers have access to.
  50  *
  51  * Most modifications are internally staged at the 'temp' vector, from which
  52  * they can be published at 'impl' by calling pvector_publish().  This saves
  53  * unnecessary memory allocations when many changes are done back-to-back.
  54  * 'temp' may contain NULL pointers and it may be in unsorted order.  It is
  55  * sorted before it is published at 'impl', which also removes the NULLs from
  56  * the published vector.
  57  */
  58
  59 struct pvector_entry {
  60     int priority;
  61     void *ptr;
  62 };
  63
  64 struct pvector_impl {
  65     size_t size;       /* Number of entries in the vector. */
  66     size_t allocated;  /* Number of allocated entries. */
  67     struct pvector_entry vector[];
  68 };
  69
  70 /* Concurrent priority vector. */
  71 struct pvector {
  72     OVSRCU_TYPE(struct pvector_impl *) impl;
  73     struct pvector_impl *temp;
  74 };
  75
  76 /* Initialization. */
  77 void pvector_init(struct pvector *);
  78 void pvector_destroy(struct pvector *);
  79
  80 /* Insertion and deletion.  These work on 'temp'.  */
  81 void pvector_insert(struct pvector *, void *, int priority);
  82 void pvector_change_priority(struct pvector *, void *, int priority);
  83 void pvector_remove(struct pvector *, void *);
  84
  85 /* Make the modified pvector available for iteration. */
  86 static inline void pvector_publish(struct pvector *);
  87
  88 /* Count.  These operate on the published pvector. */
  89 static inline size_t pvector_count(const struct pvector *);
  90 static inline bool pvector_is_empty(const struct pvector *);
  91
  92 /* Iteration.
  93  *
  94  *
  95  * Thread-safety
  96  * =============
  97  *
  98  * Iteration is safe even in a pvector that is changing concurrently.
  99  * Multiple writers must exclude each other via e.g., a mutex.
 100  *
 101  * Example
 102  * =======
 103  *
 104  *     struct my_node {
 105  *         int data;
 106  *     };
 107  *
 108  *     struct my_node elem1, elem2, *iter;
 109  *     struct pvector my_pvector;
 110  *
 111  *     pvector_init(&my_pvector);
 112  *     ...add data...
 113  *     pvector_insert(&my_pvector, &elem1, 1);
 114  *     pvector_insert(&my_pvector, &elem2, 2);
 115  *     ...
 116  *     PVECTOR_FOR_EACH (iter, &my_pvector) {
 117  *         ...operate on '*iter'...
 118  *         ...elem2 to be seen before elem1...
 119  *     }
 120  *     ...
 121  *     pvector_destroy(&my_pvector);
 122  *
 123  * There is no PVECTOR_FOR_EACH_SAFE variant as iteration is performed on RCU
 124  * protected instance of the priority vector.  Any concurrent modifications
 125  * that would be disruptive for readers (such as deletions), will be performed
 126  * on a new instance.  To see any of the modifications, a new iteration loop
 127  * has to be started.
 128  *
 129  * The PVECTOR_FOR_EACH_PRIORITY limits the iteration to entries with higher
 130  * than or equal to the given priority and allows for object lookahead.
 131  *
 132  * The iteration loop must be completed without entering the OVS RCU quiescent
 133  * period.  That is, an old iteration loop must not be continued after any
 134  * blocking IO (VLOG is non-blocking, so that is OK).
 135  */
 136 struct pvector_cursor {
 137     size_t size;        /* Number of entries in the vector. */
 138     size_t entry_idx;   /* Current index. */
 139     const struct pvector_entry *vector;
 140 };
 141
 142 static inline struct pvector_cursor pvector_cursor_init(const struct pvector *,
 143                                                         size_t n_ahead,
 144                                                         size_t obj_size);
 145 static inline void *pvector_cursor_next(struct pvector_cursor *,
 146                                         int lowest_priority,
 147                                         size_t n_ahead, size_t obj_size);
 148 static inline void pvector_cursor_lookahead(const struct pvector_cursor *,
 149                                             int n, size_t size);
 150
 151 #define PVECTOR_FOR_EACH(PTR, PVECTOR)                                  \
 152     for (struct pvector_cursor cursor__ = pvector_cursor_init(PVECTOR, 0, 0); \
 153          ((PTR) = pvector_cursor_next(&cursor__, INT_MIN, 0, 0)) != NULL; )
 154
 155 /* Loop while priority is higher than or equal to 'PRIORITY' and prefetch
 156  * objects of size 'SZ' 'N' objects ahead from the current object. */
 157 #define PVECTOR_FOR_EACH_PRIORITY(PTR, PRIORITY, N, SZ, PVECTOR)        \
 158     for (struct pvector_cursor cursor__ = pvector_cursor_init(PVECTOR, N, SZ); \
 159          ((PTR) = pvector_cursor_next(&cursor__, PRIORITY, N, SZ)) != NULL; )
 160
 161 #define PVECTOR_CURSOR_FOR_EACH(PTR, CURSOR, PVECTOR)                \
 162     for (*(CURSOR) = pvector_cursor_init(PVECTOR, 0, 0);             \
 163          ((PTR) = pvector_cursor_next(CURSOR, INT_MIN, 0, 0)) != NULL; )
 164
 165 #define PVECTOR_CURSOR_FOR_EACH_CONTINUE(PTR, CURSOR)                   \
 166     for (; ((PTR) = pvector_cursor_next(CURSOR, INT_MIN, 0, 0)) != NULL; )
 167
 168 \f
 169 /* Inline implementations. */
 170
 171 static inline struct pvector_cursor
 172 pvector_cursor_init(const struct pvector *pvec,
 173                     size_t n_ahead, size_t obj_size)
 174 {
 175     const struct pvector_impl *impl;
 176     struct pvector_cursor cursor;
 177
 178     impl = ovsrcu_get(struct pvector_impl *, &pvec->impl);
 179
 180     ovs_prefetch_range(impl->vector, impl->size * sizeof impl->vector[0]);
 181
 182     cursor.size = impl->size;
 183     cursor.vector = impl->vector;
 184     cursor.entry_idx = -1;
 185
 186     for (size_t i = 0; i < n_ahead; i++) {
 187         /* Prefetch the first objects. */
 188         pvector_cursor_lookahead(&cursor, i, obj_size);
 189     }
 190     return cursor;
 191 }
 192
 193 static inline void *pvector_cursor_next(struct pvector_cursor *cursor,
 194                                         int lowest_priority,
 195                                         size_t n_ahead, size_t obj_size)
 196 {
 197     if (++cursor->entry_idx < cursor->size &&
 198         cursor->vector[cursor->entry_idx].priority >= lowest_priority) {
 199         if (n_ahead) {
 200             pvector_cursor_lookahead(cursor, n_ahead, obj_size);
 201         }
 202         return cursor->vector[cursor->entry_idx].ptr;
 203     }
 204     return NULL;
 205 }
 206
 207 static inline void pvector_cursor_lookahead(const struct pvector_cursor *cursor,
 208                                             int n, size_t size)
 209 {
 210     if (cursor->entry_idx + n < cursor->size) {
 211         ovs_prefetch_range(cursor->vector[cursor->entry_idx + n].ptr, size);
 212     }
 213 }
 214
 215 static inline size_t pvector_count(const struct pvector *pvec)
 216 {
 217     return ovsrcu_get(struct pvector_impl *, &pvec->impl)->size;
 218 }
 219
 220 static inline bool pvector_is_empty(const struct pvector *pvec)
 221 {
 222     return pvector_count(pvec) == 0;
 223 }
 224
 225 void pvector_publish__(struct pvector *);
 226
 227 /* Make the modified pvector available for iteration. */
 228 static inline void pvector_publish(struct pvector *pvec)
 229 {
 230     if (pvec->temp) {
 231         pvector_publish__(pvec);
 232     }
 233 }
 234
 235 #endif /* pvector.h */