shared: add simple priority queue implementation

1 files changed, 281 insertions, 0 deletions

diff --git a/src/shared/prioq.c b/src/shared/prioq.c
new file mode 100644
index 0000000000..fe91324d9b
--- /dev/null
+++ b/src/shared/prioq.c
@@ -0,0 +1,281 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  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/>.
+***/
+
+#include "util.h"
+#include "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;
+}
+
+void prioq_free(Prioq *q) {
+        if (!q)
+                return;
+
+        free(q->items);
+        free(q);
+}
+
+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, 16);
+                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);
+        }
+}
+
+static struct prioq_item* find_item(Prioq *q, void *data, unsigned *idx) {
+        struct prioq_item *i;
+
+        assert(q);
+
+        if (idx) {
+                assert(*idx < q->n_items);
+                i = q->items + *idx;
+                assert(i->data == data);
+
+                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;
+
+        assert(q);
+
+        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) {
+        assert(q);
+
+        if (q->n_items <= 0)
+                return NULL;
+
+        return q->items[0].data;
+}
+
+void *prioq_pop(Prioq *q) {
+        void *data;
+
+        assert(q);
+
+        if (q->n_items <= 0)
+                return NULL;
+
+        data = q->items[0].data;
+        remove_item(q, q->items);
+        return data;
+}
+
+unsigned prioq_size(Prioq *q) {
+        assert(q);
+
+        return q->n_items;
+
+}
+bool prioq_isempty(Prioq *q) {
+        assert(q);
+
+        return q->n_items <= 0;
+}