util: Add a util_sparse_array data structure

[mesa.git] / src / util / sparse_array.h

diff --git a/src/util/sparse_array.h b/src/util/sparse_array.h
new file mode 100644 (file)
index 0000000..5736613
--- /dev/null
+++ b/src/util/sparse_array.h
@@ -0,0 +1,88 @@
+/*
+ * 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 */