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-rw-r--r--src/libsystemd-basic/src/prioq.c318
1 files changed, 318 insertions, 0 deletions
diff --git a/src/libsystemd-basic/src/prioq.c b/src/libsystemd-basic/src/prioq.c
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index 0000000000..4f43f973c3
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+++ b/src/libsystemd-basic/src/prioq.c
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+/***
+ This file is part of systemd.
+
+ Copyright 2013 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/*
+ * Priority Queue
+ * The prioq object implements a priority queue. That is, it orders objects by
+ * their priority and allows O(1) access to the object with the highest
+ * priority. Insertion and removal are Θ(log n). Optionally, the caller can
+ * provide a pointer to an index which will be kept up-to-date by the prioq.
+ *
+ * The underlying algorithm used in this implementation is a Heap.
+ */
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include "systemd-basic/alloc-util.h"
+#include "systemd-basic/hashmap.h"
+#include "systemd-basic/prioq.h"
+
+struct prioq_item {
+ void *data;
+ unsigned *idx;
+};
+
+struct Prioq {
+ compare_func_t compare_func;
+ unsigned n_items, n_allocated;
+
+ struct prioq_item *items;
+};
+
+Prioq *prioq_new(compare_func_t compare_func) {
+ Prioq *q;
+
+ q = new0(Prioq, 1);
+ if (!q)
+ return q;
+
+ q->compare_func = compare_func;
+ return q;
+}
+
+Prioq* prioq_free(Prioq *q) {
+ if (!q)
+ return NULL;
+
+ free(q->items);
+ return mfree(q);
+}
+
+int prioq_ensure_allocated(Prioq **q, compare_func_t compare_func) {
+ assert(q);
+
+ if (*q)
+ return 0;
+
+ *q = prioq_new(compare_func);
+ if (!*q)
+ return -ENOMEM;
+
+ return 0;
+}
+
+static void swap(Prioq *q, unsigned j, unsigned k) {
+ void *saved_data;
+ unsigned *saved_idx;
+
+ assert(q);
+ assert(j < q->n_items);
+ assert(k < q->n_items);
+
+ assert(!q->items[j].idx || *(q->items[j].idx) == j);
+ assert(!q->items[k].idx || *(q->items[k].idx) == k);
+
+ saved_data = q->items[j].data;
+ saved_idx = q->items[j].idx;
+ q->items[j].data = q->items[k].data;
+ q->items[j].idx = q->items[k].idx;
+ q->items[k].data = saved_data;
+ q->items[k].idx = saved_idx;
+
+ if (q->items[j].idx)
+ *q->items[j].idx = j;
+
+ if (q->items[k].idx)
+ *q->items[k].idx = k;
+}
+
+static unsigned shuffle_up(Prioq *q, unsigned idx) {
+ assert(q);
+
+ while (idx > 0) {
+ unsigned k;
+
+ k = (idx-1)/2;
+
+ if (q->compare_func(q->items[k].data, q->items[idx].data) <= 0)
+ break;
+
+ swap(q, idx, k);
+ idx = k;
+ }
+
+ return idx;
+}
+
+static unsigned shuffle_down(Prioq *q, unsigned idx) {
+ assert(q);
+
+ for (;;) {
+ unsigned j, k, s;
+
+ k = (idx+1)*2; /* right child */
+ j = k-1; /* left child */
+
+ if (j >= q->n_items)
+ break;
+
+ if (q->compare_func(q->items[j].data, q->items[idx].data) < 0)
+
+ /* So our left child is smaller than we are, let's
+ * remember this fact */
+ s = j;
+ else
+ s = idx;
+
+ if (k < q->n_items &&
+ q->compare_func(q->items[k].data, q->items[s].data) < 0)
+
+ /* So our right child is smaller than we are, let's
+ * remember this fact */
+ s = k;
+
+ /* s now points to the smallest of the three items */
+
+ if (s == idx)
+ /* No swap necessary, we're done */
+ break;
+
+ swap(q, idx, s);
+ idx = s;
+ }
+
+ return idx;
+}
+
+int prioq_put(Prioq *q, void *data, unsigned *idx) {
+ struct prioq_item *i;
+ unsigned k;
+
+ assert(q);
+
+ if (q->n_items >= q->n_allocated) {
+ unsigned n;
+ struct prioq_item *j;
+
+ n = MAX((q->n_items+1) * 2, 16u);
+ j = realloc(q->items, sizeof(struct prioq_item) * n);
+ if (!j)
+ return -ENOMEM;
+
+ q->items = j;
+ q->n_allocated = n;
+ }
+
+ k = q->n_items++;
+ i = q->items + k;
+ i->data = data;
+ i->idx = idx;
+
+ if (idx)
+ *idx = k;
+
+ shuffle_up(q, k);
+
+ return 0;
+}
+
+static void remove_item(Prioq *q, struct prioq_item *i) {
+ struct prioq_item *l;
+
+ assert(q);
+ assert(i);
+
+ l = q->items + q->n_items - 1;
+
+ if (i == l)
+ /* Last entry, let's just remove it */
+ q->n_items--;
+ else {
+ unsigned k;
+
+ /* Not last entry, let's replace the last entry with
+ * this one, and reshuffle */
+
+ k = i - q->items;
+
+ i->data = l->data;
+ i->idx = l->idx;
+ if (i->idx)
+ *i->idx = k;
+ q->n_items--;
+
+ k = shuffle_down(q, k);
+ shuffle_up(q, k);
+ }
+}
+
+_pure_ static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
+ struct prioq_item *i;
+
+ assert(q);
+
+ if (idx) {
+ if (*idx == PRIOQ_IDX_NULL ||
+ *idx > q->n_items)
+ return NULL;
+
+ i = q->items + *idx;
+ if (i->data != data)
+ return NULL;
+
+ return i;
+ } else {
+ for (i = q->items; i < q->items + q->n_items; i++)
+ if (i->data == data)
+ return i;
+ return NULL;
+ }
+}
+
+int prioq_remove(Prioq *q, void *data, unsigned *idx) {
+ struct prioq_item *i;
+
+ if (!q)
+ return 0;
+
+ i = find_item(q, data, idx);
+ if (!i)
+ return 0;
+
+ remove_item(q, i);
+ return 1;
+}
+
+int prioq_reshuffle(Prioq *q, void *data, unsigned *idx) {
+ struct prioq_item *i;
+ unsigned k;
+
+ assert(q);
+
+ i = find_item(q, data, idx);
+ if (!i)
+ return 0;
+
+ k = i - q->items;
+ k = shuffle_down(q, k);
+ shuffle_up(q, k);
+ return 1;
+}
+
+void *prioq_peek(Prioq *q) {
+
+ if (!q)
+ return NULL;
+
+ if (q->n_items <= 0)
+ return NULL;
+
+ return q->items[0].data;
+}
+
+void *prioq_pop(Prioq *q) {
+ void *data;
+
+ if (!q)
+ return NULL;
+
+ if (q->n_items <= 0)
+ return NULL;
+
+ data = q->items[0].data;
+ remove_item(q, q->items);
+ return data;
+}
+
+unsigned prioq_size(Prioq *q) {
+
+ if (!q)
+ return 0;
+
+ return q->n_items;
+}
+
+bool prioq_isempty(Prioq *q) {
+
+ if (!q)
+ return true;
+
+ return q->n_items <= 0;
+}
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