2 This file is part of systemd.
4 Copyright 2013 Lennart Poettering
6 systemd is free software; you can redistribute it and/or modify it
7 under the terms of the GNU Lesser General Public License as published by
8 the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version.
11 systemd is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public License
17 along with systemd; If not, see <http://www.gnu.org/licenses/>.
22 * The prioq object implements a priority queue. That is, it orders objects by
23 * their priority and allows O(1) access to the object with the highest
24 * priority. Insertion and removal are Θ(log n). Optionally, the caller can
25 * provide a pointer to an index which will be kept up-to-date by the prioq.
27 * The underlying algorithm used in this implementation is a Heap.
33 #include "alloc-util.h"
43 compare_func_t compare_func;
44 unsigned n_items, n_allocated;
46 struct prioq_item *items;
49 Prioq *prioq_new(compare_func_t compare_func) {
56 q->compare_func = compare_func;
60 Prioq* prioq_free(Prioq *q) {
68 int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) {
74 *q = prioq_new(compare_func);
81 static void swap(Prioq *q, unsigned j, unsigned k) {
86 assert(j < q->n_items);
87 assert(k < q->n_items);
89 assert(!q->items[j].idx || *(q->items[j].idx) == j);
90 assert(!q->items[k].idx || *(q->items[k].idx) == k);
92 saved_data = q->items[j].data;
93 saved_idx = q->items[j].idx;
94 q->items[j].data = q->items[k].data;
95 q->items[j].idx = q->items[k].idx;
96 q->items[k].data = saved_data;
97 q->items[k].idx = saved_idx;
100 *q->items[j].idx = j;
103 *q->items[k].idx = k;
106 static unsigned shuffle_up(Prioq *q, unsigned idx) {
114 if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0)
124 static unsigned shuffle_down(Prioq *q, unsigned idx) {
130 k = (idx+1)*2; /* right child */
131 j = k-1; /* left child */
136 if (q->compare_func(q->items[j].data, q->items[idx].data) < 0)
138 /* So our left child is smaller than we are, let's
139 * remember this fact */
144 if (k < q->n_items &&
145 q->compare_func(q->items[k].data, q->items[s].data) < 0)
147 /* So our right child is smaller than we are, let's
148 * remember this fact */
151 /* s now points to the smallest of the three items */
154 /* No swap necessary, we're done */
164 int prioq_put(Prioq *q, void *data, unsigned *idx) {
165 struct prioq_item *i;
170 if (q->n_items >= q->n_allocated) {
172 struct prioq_item *j;
174 n = MAX((q->n_items+1) * 2, 16u);
175 j = realloc(q->items, sizeof(struct prioq_item) * n);
196 static void remove_item(Prioq *q, struct prioq_item *i) {
197 struct prioq_item *l;
202 l = q->items + q->n_items - 1;
205 /* Last entry, let's just remove it */
210 /* Not last entry, let's replace the last entry with
211 * this one, and reshuffle */
221 k = shuffle_down(q, k);
226 _pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
227 struct prioq_item *i;
232 if (*idx == PRIOQ_IDX_NULL ||
242 for (i = q->items; i < q->items + q->n_items; i++)
249 int prioq_remove(Prioq *q, void *data, unsigned *idx) {
250 struct prioq_item *i;
255 i = find_item(q, data, idx);
263 int prioq_reshuffle(Prioq *q, void *data, unsigned *idx) {
264 struct prioq_item *i;
269 i = find_item(q, data, idx);
274 k = shuffle_down(q, k);
279 void *prioq_peek(Prioq *q) {
287 return q->items[0].data;
290 void *prioq_pop(Prioq *q) {
299 data = q->items[0].data;
300 remove_item(q, q->items);
304 unsigned prioq_size(Prioq *q) {
312 bool prioq_isempty(Prioq *q) {
317 return q->n_items <= 0;