1 /*
2 ** GNU Pth - The GNU Portable Threads
3 ** Copyright (c) 1999-2006 Ralf S. Engelschall <rse@engelschall.com>
4 **
5 ** This file is part of GNU Pth, a non-preemptive thread scheduling
6 ** library which can be found at http://www.gnu.org/software/pth/.
7 **
8 ** This library is free software; you can redistribute it and/or
9 ** modify it under the terms of the GNU Lesser General Public
10 ** License as published by the Free Software Foundation; either
11 ** version 2.1 of the License, or (at your option) any later version.
12 **
13 ** This library is distributed in the hope that it will be useful,
14 ** but WITHOUT ANY WARRANTY; without even the implied warranty of
15 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 ** Lesser General Public License for more details.
17 **
18 ** You should have received a copy of the GNU Lesser General Public
19 ** License along with this library; if not, write to the Free Software
20 ** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
21 ** USA, or contact Ralf S. Engelschall <rse@engelschall.com>.
22 **
23 ** pth_ring.c: Pth ring data structure
24 */
25 /* ``Unix was not designed to stop people
26 from doing stupid things, because that
27 would also stop them from doing clever
28 things.'' --Doug Gwyn */
29
30 /*
31 * This is a "ring" data structure, a special case of a list. It is
32 * implemented through double-chained nodes. The link structure is part
33 * of the nodes, i.e. no extra memory is required for the ring itself
34 * and the ring can contain as many nodes as fit into memory. The main
35 * advantage of using a ring instead of a plain list is to make the ring
36 * operations easier (less special cases!). The ring is usually used
37 * in Pth to represent a "set" of something. All operations are O(1),
38 * except for the check whether a node is part of the ring (which is
39 * O(N)).
40 */
41
42 #include "pth_p.h"
43
44 /* initialize ring; O(1) */
pth_ring_init(pth_ring_t * r)45 intern void pth_ring_init(pth_ring_t *r)
46 {
47 if (r == NULL)
48 return;
49 r->r_hook = NULL;
50 r->r_nodes = 0;
51 return;
52 }
53
54 /* return number of nodes in ring; O(1) */
55 #if cpp
56 #define pth_ring_elements(r) \
57 ((r) == NULL ? (-1) : (r)->r_nodes)
58 #endif
59
60 /* return first node in ring; O(1) */
61 #if cpp
62 #define pth_ring_first(r) \
63 ((r) == NULL ? NULL : (r)->r_hook)
64 #endif
65
66 /* return last node in ring; O(1) */
67 #if cpp
68 #define pth_ring_last(r) \
69 ((r) == NULL ? NULL : ((r)->r_hook == NULL ? NULL : (r)->r_hook->rn_prev))
70 #endif
71
72 /* walk to next node in ring; O(1) */
73 #if cpp
74 #define pth_ring_next(r, rn) \
75 (((r) == NULL || (rn) == NULL) ? NULL : ((rn)->rn_next == (r)->r_hook ? NULL : (rn)->rn_next))
76 #endif
77
78 /* walk to previous node in ring; O(1) */
79 #if cpp
80 #define pth_ring_prev(r, rn) \
81 (((r) == NULL || (rn) == NULL) ? NULL : ((rn)->rn_prev == (r)->r_hook->rn_prev ? NULL : (rn)->rn_prev))
82 #endif
83
84 /* insert node into ring; O(1) */
85 #if cpp
86 #define pth_ring_insert(r, rn) \
87 pth_ring_append((r), (rn))
88 #endif
89
90 /* insert node after a second node in ring; O(1) */
pth_ring_insert_after(pth_ring_t * r,pth_ringnode_t * rn1,pth_ringnode_t * rn2)91 intern void pth_ring_insert_after(pth_ring_t *r, pth_ringnode_t *rn1, pth_ringnode_t *rn2)
92 {
93 if (r == NULL || rn1 == NULL || rn2 == NULL)
94 return;
95 rn2->rn_prev = rn1;
96 rn2->rn_next = rn1->rn_next;
97 rn2->rn_prev->rn_next = rn2;
98 rn2->rn_next->rn_prev = rn2;
99 r->r_nodes++;
100 return;
101 }
102
103 /* insert node before a second node in ring; O(1) */
pth_ring_insert_before(pth_ring_t * r,pth_ringnode_t * rn1,pth_ringnode_t * rn2)104 intern void pth_ring_insert_before(pth_ring_t *r, pth_ringnode_t *rn1, pth_ringnode_t *rn2)
105 {
106 if (r == NULL || rn1 == NULL || rn2 == NULL)
107 return;
108 rn2->rn_next = rn1;
109 rn2->rn_prev = rn1->rn_prev;
110 rn2->rn_prev->rn_next = rn2;
111 rn2->rn_next->rn_prev = rn2;
112 r->r_nodes++;
113 return;
114 }
115
116 /* delete an node from ring; O(1) */
pth_ring_delete(pth_ring_t * r,pth_ringnode_t * rn)117 intern void pth_ring_delete(pth_ring_t *r, pth_ringnode_t *rn)
118 {
119 if (r == NULL || rn == NULL)
120 return;
121 if (r->r_hook == rn && rn->rn_prev == rn && rn->rn_next == rn)
122 r->r_hook = NULL;
123 else {
124 if (r->r_hook == rn)
125 r->r_hook = rn->rn_next;
126 rn->rn_prev->rn_next = rn->rn_next;
127 rn->rn_next->rn_prev = rn->rn_prev;
128 }
129 r->r_nodes--;
130 return;
131 }
132
133 /* prepend an node to ring; O(1) */
pth_ring_prepend(pth_ring_t * r,pth_ringnode_t * rn)134 intern void pth_ring_prepend(pth_ring_t *r, pth_ringnode_t *rn)
135 {
136 if (r == NULL || rn == NULL)
137 return;
138 if (r->r_hook == NULL) {
139 r->r_hook = rn;
140 rn->rn_next = rn;
141 rn->rn_prev = rn;
142 }
143 else {
144 rn->rn_next = r->r_hook;
145 rn->rn_prev = r->r_hook->rn_prev;
146 rn->rn_next->rn_prev = rn;
147 rn->rn_prev->rn_next = rn;
148 r->r_hook = rn;
149 }
150 r->r_nodes++;
151 return;
152 }
153
154 /* append an node to ring; O(1) */
pth_ring_append(pth_ring_t * r,pth_ringnode_t * rn)155 intern void pth_ring_append(pth_ring_t *r, pth_ringnode_t *rn)
156 {
157 if (r == NULL || rn == NULL)
158 return;
159 if (r->r_hook == NULL) {
160 r->r_hook = rn;
161 rn->rn_next = rn;
162 rn->rn_prev = rn;
163 }
164 else {
165 rn->rn_next = r->r_hook;
166 rn->rn_prev = r->r_hook->rn_prev;
167 rn->rn_next->rn_prev = rn;
168 rn->rn_prev->rn_next = rn;
169 }
170 r->r_nodes++;
171 return;
172 }
173
174 /* treat ring as stack: push node onto stack; O(1) */
175 #if cpp
176 #define pth_ring_push(r, rn) \
177 pth_ring_prepend((r), (rn))
178 #endif
179
180 /* treat ring as stack: pop node from stack; O(1) */
pth_ring_pop(pth_ring_t * r)181 intern pth_ringnode_t *pth_ring_pop(pth_ring_t *r)
182 {
183 pth_ringnode_t *rn;
184
185 rn = pth_ring_first(r);
186 if (rn != NULL)
187 pth_ring_delete(r, rn);
188 return rn;
189 }
190
191 /* treat ring as queue: favorite a node in the ring; O(1) */
pth_ring_favorite(pth_ring_t * r,pth_ringnode_t * rn)192 intern int pth_ring_favorite(pth_ring_t *r, pth_ringnode_t *rn)
193 {
194 if (r == NULL)
195 return FALSE;
196 if (r->r_hook == NULL)
197 return FALSE;
198 /* element is perhaps already at ring hook */
199 if (r->r_hook == rn)
200 return TRUE;
201 /* move to hook of ring */
202 pth_ring_delete(r, rn);
203 pth_ring_prepend(r, rn);
204 return TRUE;
205 }
206
207 /* treat ring as queue: enqueue node; O(1) */
208 #if cpp
209 #define pth_ring_enqueue(r, rn) \
210 pth_ring_prepend((r), (rn))
211 #endif
212
213 /* treat ring as queue: dequeue node; O(1) */
pth_ring_dequeue(pth_ring_t * r)214 intern pth_ringnode_t *pth_ring_dequeue(pth_ring_t *r)
215 {
216 pth_ringnode_t *rn;
217
218 rn = pth_ring_last(r);
219 if (rn != NULL)
220 pth_ring_delete(r, rn);
221 return rn;
222 }
223
224 /* check whether node is contained in ring; O(n) */
pth_ring_contains(pth_ring_t * r,pth_ringnode_t * rns)225 intern int pth_ring_contains(pth_ring_t *r, pth_ringnode_t *rns)
226 {
227 pth_ringnode_t *rn;
228 int rc;
229
230 if (r == NULL || rns == NULL)
231 return pth_error(FALSE, EINVAL);
232 rc = FALSE;
233 rn = r->r_hook;
234 if (rn != NULL) {
235 do {
236 if (rn == rns) {
237 rc = TRUE;
238 break;
239 }
240 rn = rn->rn_next;
241 } while (rn != r->r_hook);
242 }
243 return rc;
244 }
245
246