/*-*- 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/>. ***/ /* * 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 "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; } Prioq* prioq_free(Prioq *q) { if (!q) return NULL; free(q->items); free(q); return NULL; } 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; }