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/*
* Copyright © 2019 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifndef _UTIL_SPARSE_ARRAY_H
#define _UTIL_SPARSE_ARRAY_H
#include <stdint.h>
#include "c11/threads.h"
#include "macros.h"
#include "u_atomic.h"
#include "u_math.h"
#ifdef __cplusplus
extern "C" {
#endif
struct util_sparse_array_node;
/** A thread-safe automatically growing sparse array data structure
*
* This data structure has the following very nice properties:
*
* 1. Accessing an element is basically constant time. Technically, it's
* O(log_b n) where the base b is the node size and n is the maximum
* index. However, node sizes are expected to be fairly large and the
* index is a uint64_t so, if your node size is 256, it's O(8).
*
* 2. The data stored in the array is never moved in memory. Instead, the
* data structure only ever grows and new nodes are added as-needed. This
* means it's safe to store a pointer to something stored in the sparse
* array without worrying about a realloc invalidating it.
*
* 3. The data structure is thread-safe. No guarantees are made about the
* data stored in the sparse array but it is safe to call
* util_sparse_array_get(arr, idx) from as many threads as you'd like and
* we guarantee that two calls to util_sparse_array_get(arr, idx) with the
* same array and index will always return the same pointer regardless
* contention between threads.
*
* 4. The data structure is lock-free. All manipulations of the tree are
* done by a careful use of atomics to maintain thread safety and no locks
* are ever taken other than those taken implicitly by calloc(). If no
* allocation is required, util_sparse_array_get(arr, idx) does a simple
* walk over the tree should be efficient even in the case where many
* threads are accessing the sparse array at once.
*/
struct util_sparse_array {
size_t elem_size;
unsigned node_size_log2;
struct util_sparse_array_node *root;
};
void util_sparse_array_init(struct util_sparse_array *arr,
size_t elem_size, size_t node_size);
void util_sparse_array_finish(struct util_sparse_array *arr);
void *util_sparse_array_get(struct util_sparse_array *arr, uint64_t idx);
void util_sparse_array_validate(struct util_sparse_array *arr);
#ifdef __cplusplus
} /* extern C */
#endif
#endif /* _UTIL_SPARSE_ARRAY_H */
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