mirror of
https://github.com/openvswitch/ovs
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250 lines
9.0 KiB
C
250 lines
9.0 KiB
C
/*
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* Copyright (c) 2014, 2016 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef PVECTOR_H
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#define PVECTOR_H 1
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#include <stdbool.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include "ovs-rcu.h"
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#include "util.h"
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/* Concurrent Priority Vector
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* ==========================
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*
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* Concurrent priority vector holds non-NULL pointers to objects in a
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* nondecreasing priority order and allows readers to traverse the vector
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* without being concerned about writers modifying the vector as they are
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* traversing it.
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*
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* Multiple elements of a given priority are allowed.
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*
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* The priority order is maintained as a linear vector of elements to allow
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* for efficient memory prefetching.
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*
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* Concurrency is implemented with OVS RCU so that the readers can assume
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* that once they have taken a pointer to the vector with
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* pvector_cursor_init(), the 'size' member will not decrease, so that
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* they can safely read 'size' entries from 'vector', and find that each
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* entry has a valid, non-NULL 'ptr', and the vector is in order from highest
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* to lowest 'priority'. The 'priority' values can change any time, but only
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* so that the order of the entries does not change, so readers can use
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* 'priority' values read at any time after acquisition of the vector pointer.
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*
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* Writers can concurrently add entries to the end of the vector, incrementing
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* 'size', or update the 'priority' value of an entry, but only if that does
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* not change the ordering of the entries. Writers will never change the 'ptr'
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* values, or decrement the 'size' on a copy that readers have access to.
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*
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* Most modifications are internally staged at the 'temp' vector, from which
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* they can be published at 'impl' by calling pvector_publish(). This saves
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* unnecessary memory allocations when many changes are done back-to-back.
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* 'temp' may contain NULL pointers and it may be in unsorted order. It is
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* sorted before it is published at 'impl', which also removes the NULLs from
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* the published vector.
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*
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* Since the vector is RCU protected, the entry destruction after removal must
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* be RCU postponed. Also, if it happens before changes published with
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* pvector_publish(), destruction must be double postponed, i.e., the second
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* ovsrcu_postpone() call to destruct the entry should be called from the first
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* RCU callback. This is required because readers could still obtain the
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* unmodified vector until updated version is published.
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*/
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struct pvector_entry {
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int priority;
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void *ptr;
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};
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struct pvector_impl {
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atomic_size_t size; /* Number of entries in the vector. */
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size_t allocated; /* Number of allocated entries. */
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struct pvector_entry vector[];
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};
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/* Concurrent priority vector. */
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struct pvector {
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OVSRCU_TYPE(struct pvector_impl *) impl;
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struct pvector_impl *temp;
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};
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/* Initialization. */
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void pvector_init(struct pvector *);
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void pvector_destroy(struct pvector *);
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/* Insertion and deletion. These work on 'temp'. */
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void pvector_insert(struct pvector *, void *, int priority);
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void pvector_change_priority(struct pvector *, void *, int priority);
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void pvector_remove(struct pvector *, void *);
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/* Make the modified pvector available for iteration. */
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static inline void pvector_publish(struct pvector *);
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/* Count. These operate on the published pvector. */
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static inline size_t pvector_count(const struct pvector *);
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static inline bool pvector_is_empty(const struct pvector *);
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/* Iteration.
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*
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*
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* Thread-safety
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* =============
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*
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* Iteration is safe even in a pvector that is changing concurrently.
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* Multiple writers must exclude each other via e.g., a mutex.
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*
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* Example
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* =======
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*
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* struct my_node {
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* int data;
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* };
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*
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* struct my_node elem1, elem2, *iter;
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* struct pvector my_pvector;
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*
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* pvector_init(&my_pvector);
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* ...add data...
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* pvector_insert(&my_pvector, &elem1, 1);
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* pvector_insert(&my_pvector, &elem2, 2);
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* ...
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* PVECTOR_FOR_EACH (iter, &my_pvector) {
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* ...operate on '*iter'...
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* ...elem2 to be seen before elem1...
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* }
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* ...
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* pvector_destroy(&my_pvector);
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*
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* There is no PVECTOR_FOR_EACH_SAFE variant as iteration is performed on RCU
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* protected instance of the priority vector. Any concurrent modifications
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* that would be disruptive for readers (such as deletions), will be performed
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* on a new instance. To see any of the modifications, a new iteration loop
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* has to be started.
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*
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* The PVECTOR_FOR_EACH_PRIORITY limits the iteration to entries with higher
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* than or equal to the given priority and allows for object lookahead.
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*
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* The iteration loop must be completed without entering the OVS RCU quiescent
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* period. That is, an old iteration loop must not be continued after any
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* blocking IO (VLOG is non-blocking, so that is OK).
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*/
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struct pvector_cursor {
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size_t size; /* Number of entries in the vector. */
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size_t entry_idx; /* Current index. */
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const struct pvector_entry *vector;
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};
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static inline struct pvector_cursor pvector_cursor_init(const struct pvector *,
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size_t n_ahead,
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size_t obj_size);
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static inline void *pvector_cursor_next(struct pvector_cursor *,
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int lowest_priority,
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size_t n_ahead, size_t obj_size);
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static inline void pvector_cursor_lookahead(const struct pvector_cursor *,
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int n, size_t size);
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#define PVECTOR_FOR_EACH(PTR, PVECTOR) \
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for (struct pvector_cursor cursor__ = pvector_cursor_init(PVECTOR, 0, 0); \
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((PTR) = pvector_cursor_next(&cursor__, INT_MIN, 0, 0)) != NULL; )
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/* Loop while priority is higher than or equal to 'PRIORITY' and prefetch
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* objects of size 'SZ' 'N' objects ahead from the current object. */
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#define PVECTOR_FOR_EACH_PRIORITY(PTR, PRIORITY, N, SZ, PVECTOR) \
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for (struct pvector_cursor cursor__ = pvector_cursor_init(PVECTOR, N, SZ); \
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((PTR) = pvector_cursor_next(&cursor__, PRIORITY, N, SZ)) != NULL; )
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#define PVECTOR_CURSOR_FOR_EACH(PTR, CURSOR, PVECTOR) \
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for (*(CURSOR) = pvector_cursor_init(PVECTOR, 0, 0); \
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((PTR) = pvector_cursor_next(CURSOR, INT_MIN, 0, 0)) != NULL; )
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#define PVECTOR_CURSOR_FOR_EACH_CONTINUE(PTR, CURSOR) \
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for (; ((PTR) = pvector_cursor_next(CURSOR, INT_MIN, 0, 0)) != NULL; )
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/* Inline implementations. */
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static inline struct pvector_cursor
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pvector_cursor_init(const struct pvector *pvec,
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size_t n_ahead, size_t obj_size)
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{
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const struct pvector_impl *impl;
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struct pvector_cursor cursor;
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size_t size;
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impl = ovsrcu_get(struct pvector_impl *, &pvec->impl);
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/* Use memory_order_acquire to ensure entry access can not be
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* reordered to happen before size read. */
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atomic_read_explicit(&CONST_CAST(struct pvector_impl *, impl)->size,
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&size, memory_order_acquire);
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ovs_prefetch_range(impl->vector, size * sizeof impl->vector[0]);
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cursor.size = size;
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cursor.vector = impl->vector;
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cursor.entry_idx = -1;
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for (size_t i = 0; i < n_ahead; i++) {
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/* Prefetch the first objects. */
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pvector_cursor_lookahead(&cursor, i, obj_size);
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}
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return cursor;
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}
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static inline void *pvector_cursor_next(struct pvector_cursor *cursor,
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int lowest_priority,
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size_t n_ahead, size_t obj_size)
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{
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if (++cursor->entry_idx < cursor->size &&
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cursor->vector[cursor->entry_idx].priority >= lowest_priority) {
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if (n_ahead) {
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pvector_cursor_lookahead(cursor, n_ahead, obj_size);
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}
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return cursor->vector[cursor->entry_idx].ptr;
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}
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return NULL;
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}
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static inline void pvector_cursor_lookahead(const struct pvector_cursor *cursor,
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int n, size_t size)
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{
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if (cursor->entry_idx + n < cursor->size) {
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ovs_prefetch_range(cursor->vector[cursor->entry_idx + n].ptr, size);
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}
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}
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static inline size_t pvector_count(const struct pvector *pvec)
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{
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return ovsrcu_get(struct pvector_impl *, &pvec->impl)->size;
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}
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static inline bool pvector_is_empty(const struct pvector *pvec)
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{
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return pvector_count(pvec) == 0;
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}
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void pvector_publish__(struct pvector *);
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/* Make the modified pvector available for iteration. */
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static inline void pvector_publish(struct pvector *pvec)
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{
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if (pvec->temp) {
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pvector_publish__(pvec);
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}
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}
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#endif /* pvector.h */
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