320 lines
7.3 KiB
C
320 lines
7.3 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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/***
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This file is part of systemd.
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Copyright 2013 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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/*
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* Priority Queue
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* The prioq object implements a priority queue. That is, it orders objects by
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* their priority and allows O(1) access to the object with the highest
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* priority. Insertion and removal are Θ(log n). Optionally, the caller can
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* provide a pointer to an index which will be kept up-to-date by the prioq.
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*
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* The underlying algorithm used in this implementation is a Heap.
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*/
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#include <errno.h>
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#include <stdlib.h>
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#include "alloc-util.h"
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#include "hashmap.h"
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#include "prioq.h"
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struct prioq_item {
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void *data;
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unsigned *idx;
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};
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struct Prioq {
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compare_func_t compare_func;
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unsigned n_items, n_allocated;
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struct prioq_item *items;
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};
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Prioq *prioq_new(compare_func_t compare_func) {
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Prioq *q;
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q = new0(Prioq, 1);
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if (!q)
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return q;
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q->compare_func = compare_func;
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return q;
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}
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Prioq* prioq_free(Prioq *q) {
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if (!q)
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return NULL;
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free(q->items);
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return mfree(q);
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}
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int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) {
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assert(q);
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if (*q)
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return 0;
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*q = prioq_new(compare_func);
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if (!*q)
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return -ENOMEM;
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return 0;
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}
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static void swap(Prioq *q, unsigned j, unsigned k) {
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void *saved_data;
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unsigned *saved_idx;
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assert(q);
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assert(j < q->n_items);
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assert(k < q->n_items);
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assert(!q->items[j].idx || *(q->items[j].idx) == j);
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assert(!q->items[k].idx || *(q->items[k].idx) == k);
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saved_data = q->items[j].data;
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saved_idx = q->items[j].idx;
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q->items[j].data = q->items[k].data;
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q->items[j].idx = q->items[k].idx;
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q->items[k].data = saved_data;
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q->items[k].idx = saved_idx;
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if (q->items[j].idx)
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*q->items[j].idx = j;
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if (q->items[k].idx)
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*q->items[k].idx = k;
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}
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static unsigned shuffle_up(Prioq *q, unsigned idx) {
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assert(q);
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while (idx > 0) {
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unsigned k;
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k = (idx-1)/2;
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if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0)
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break;
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swap(q, idx, k);
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idx = k;
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}
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return idx;
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}
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static unsigned shuffle_down(Prioq *q, unsigned idx) {
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assert(q);
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for (;;) {
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unsigned j, k, s;
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k = (idx+1)*2; /* right child */
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j = k-1; /* left child */
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if (j >= q->n_items)
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break;
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if (q->compare_func(q->items[j].data, q->items[idx].data) < 0)
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/* So our left child is smaller than we are, let's
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* remember this fact */
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s = j;
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else
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s = idx;
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if (k < q->n_items &&
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q->compare_func(q->items[k].data, q->items[s].data) < 0)
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/* So our right child is smaller than we are, let's
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* remember this fact */
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s = k;
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/* s now points to the smallest of the three items */
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if (s == idx)
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/* No swap necessary, we're done */
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break;
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swap(q, idx, s);
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idx = s;
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}
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return idx;
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}
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int prioq_put(Prioq *q, void *data, unsigned *idx) {
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struct prioq_item *i;
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unsigned k;
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assert(q);
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if (q->n_items >= q->n_allocated) {
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unsigned n;
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struct prioq_item *j;
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n = MAX((q->n_items+1) * 2, 16u);
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j = reallocarray(q->items, n, sizeof(struct prioq_item));
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if (!j)
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return -ENOMEM;
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q->items = j;
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q->n_allocated = n;
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}
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k = q->n_items++;
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i = q->items + k;
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i->data = data;
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i->idx = idx;
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if (idx)
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*idx = k;
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shuffle_up(q, k);
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return 0;
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}
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static void remove_item(Prioq *q, struct prioq_item *i) {
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struct prioq_item *l;
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assert(q);
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assert(i);
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l = q->items + q->n_items - 1;
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if (i == l)
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/* Last entry, let's just remove it */
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q->n_items--;
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else {
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unsigned k;
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/* Not last entry, let's replace the last entry with
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* this one, and reshuffle */
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k = i - q->items;
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i->data = l->data;
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i->idx = l->idx;
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if (i->idx)
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*i->idx = k;
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q->n_items--;
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k = shuffle_down(q, k);
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shuffle_up(q, k);
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}
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}
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_pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
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struct prioq_item *i;
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assert(q);
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if (idx) {
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if (*idx == PRIOQ_IDX_NULL ||
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*idx > q->n_items)
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return NULL;
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i = q->items + *idx;
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if (i->data != data)
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return NULL;
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return i;
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} else {
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for (i = q->items; i < q->items + q->n_items; i++)
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if (i->data == data)
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return i;
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return NULL;
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}
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}
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int prioq_remove(Prioq *q, void *data, unsigned *idx) {
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struct prioq_item *i;
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if (!q)
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return 0;
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i = find_item(q, data, idx);
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if (!i)
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return 0;
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remove_item(q, i);
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return 1;
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}
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int prioq_reshuffle(Prioq *q, void *data, unsigned *idx) {
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struct prioq_item *i;
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unsigned k;
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assert(q);
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i = find_item(q, data, idx);
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if (!i)
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return 0;
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k = i - q->items;
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k = shuffle_down(q, k);
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shuffle_up(q, k);
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return 1;
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}
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void *prioq_peek(Prioq *q) {
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if (!q)
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return NULL;
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if (q->n_items <= 0)
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return NULL;
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return q->items[0].data;
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}
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void *prioq_pop(Prioq *q) {
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void *data;
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if (!q)
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return NULL;
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if (q->n_items <= 0)
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return NULL;
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data = q->items[0].data;
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remove_item(q, q->items);
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return data;
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}
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unsigned prioq_size(Prioq *q) {
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if (!q)
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return 0;
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return q->n_items;
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}
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bool prioq_isempty(Prioq *q) {
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if (!q)
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return true;
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return q->n_items <= 0;
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}
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