Apache Portable Runtime
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apr_ring.h
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1/* Licensed to the Apache Software Foundation (ASF) under one or more
2 * contributor license agreements. See the NOTICE file distributed with
3 * this work for additional information regarding copyright ownership.
4 * The ASF licenses this file to You under the Apache License, Version 2.0
5 * (the "License"); you may not use this file except in compliance with
6 * the License. You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/*
18 * This code draws heavily from the 4.4BSD <sys/queue.h> macros
19 * and Dean Gaudet's "splim/ring.h".
20 * <http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/sys/queue.h>
21 * <http://www.arctic.org/~dean/splim/>
22 *
23 * We'd use Dean's code directly if we could guarantee the
24 * availability of inline functions.
25 */
26
27#ifndef APR_RING_H
28#define APR_RING_H
29
30/**
31 * @file apr_ring.h
32 * @brief APR Rings
33 */
34
35/*
36 * for offsetof()
37 */
38#include "apr_general.h"
39
40/**
41 * @defgroup apr_ring Ring Macro Implementations
42 * @ingroup APR
43 * A ring is a kind of doubly-linked list that can be manipulated
44 * without knowing where its head is.
45 * @{
46 */
47
48/**
49 * The Ring Element
50 *
51 * A ring element struct is linked to the other elements in the ring
52 * through its ring entry field, e.g.
53 * <pre>
54 * struct my_element_t {
55 * APR_RING_ENTRY(my_element_t) link;
56 * int foo;
57 * char *bar;
58 * };
59 * </pre>
60 *
61 * An element struct may be put on more than one ring if it has more
62 * than one APR_RING_ENTRY field. Each APR_RING_ENTRY has a corresponding
63 * APR_RING_HEAD declaration.
64 *
65 * @warning For strict C standards compliance you should put the APR_RING_ENTRY
66 * first in the element struct unless the head is always part of a larger
67 * object with enough earlier fields to accommodate the offsetof() used
68 * to compute the ring sentinel below. You can usually ignore this caveat.
69 */
70#define APR_RING_ENTRY(elem) \
71 struct { \
72 struct elem * volatile next; \
73 struct elem * volatile prev; \
74 }
75
76/**
77 * The Ring Head
78 *
79 * Each ring is managed via its head, which is a struct declared like this:
80 * <pre>
81 * APR_RING_HEAD(my_ring_t, my_element_t);
82 * struct my_ring_t ring, *ringp;
83 * </pre>
84 *
85 * This struct looks just like the element link struct so that we can
86 * be sure that the typecasting games will work as expected.
87 *
88 * The first element in the ring is next after the head, and the last
89 * element is just before the head.
90 */
91#define APR_RING_HEAD(head, elem) \
92 struct head { \
93 struct elem * volatile next; \
94 struct elem * volatile prev; \
95 }
96
97/**
98 * The Ring Sentinel
99 *
100 * This is the magic pointer value that occurs before the first and
101 * after the last elements in the ring, computed from the address of
102 * the ring's head. The head itself isn't an element, but in order to
103 * get rid of all the special cases when dealing with the ends of the
104 * ring, we play typecasting games to make it look like one.
105 *
106 * Here is a diagram to illustrate the arrangements of the next and
107 * prev pointers of each element in a single ring. Note that they point
108 * to the start of each element, not to the APR_RING_ENTRY structure.
109 *
110 * <pre>
111 * +->+------+<-+ +->+------+<-+ +->+------+<-+
112 * | |struct| | | |struct| | | |struct| |
113 * / | elem | \/ | elem | \/ | elem | \
114 * ... | | /\ | | /\ | | ...
115 * +------+ | | +------+ | | +------+
116 * ...--|prev | | +--|ring | | +--|prev |
117 * | next|--+ | entry|--+ | next|--...
118 * +------+ +------+ +------+
119 * | etc. | | etc. | | etc. |
120 * : : : : : :
121 * </pre>
122 *
123 * The APR_RING_HEAD is nothing but a bare APR_RING_ENTRY. The prev
124 * and next pointers in the first and last elements don't actually
125 * point to the head, they point to a phantom place called the
126 * sentinel. Its value is such that last->next->next == first because
127 * the offset from the sentinel to the head's next pointer is the same
128 * as the offset from the start of an element to its next pointer.
129 * This also works in the opposite direction.
130 *
131 * <pre>
132 * last first
133 * +->+------+<-+ +->sentinel<-+ +->+------+<-+
134 * | |struct| | | | | |struct| |
135 * / | elem | \/ \/ | elem | \
136 * ... | | /\ /\ | | ...
137 * +------+ | | +------+ | | +------+
138 * ...--|prev | | +--|ring | | +--|prev |
139 * | next|--+ | head|--+ | next|--...
140 * +------+ +------+ +------+
141 * | etc. | | etc. |
142 * : : : :
143 * </pre>
144 *
145 * Note that the offset mentioned above is different for each kind of
146 * ring that the element may be on, and each kind of ring has a unique
147 * name for its APR_RING_ENTRY in each element, and has its own type
148 * for its APR_RING_HEAD.
149 *
150 * Note also that if the offset is non-zero (which is required if an
151 * element has more than one APR_RING_ENTRY), the unreality of the
152 * sentinel may have bad implications on very perverse implementations
153 * of C -- see the warning in APR_RING_ENTRY.
154 *
155 * @param hp The head of the ring
156 * @param elem The name of the element struct
157 * @param link The name of the APR_RING_ENTRY in the element struct
158 */
159#define APR_RING_SENTINEL(hp, elem, link) \
160 (struct elem *)((char *)(&(hp)->next) - APR_OFFSETOF(struct elem, link))
161
162/**
163 * The first element of the ring
164 * @param hp The head of the ring
165 */
166#define APR_RING_FIRST(hp) (hp)->next
167/**
168 * The last element of the ring
169 * @param hp The head of the ring
170 */
171#define APR_RING_LAST(hp) (hp)->prev
172/**
173 * The next element in the ring
174 * @param ep The current element
175 * @param link The name of the APR_RING_ENTRY in the element struct
176 */
177#define APR_RING_NEXT(ep, link) (ep)->link.next
178/**
179 * The previous element in the ring
180 * @param ep The current element
181 * @param link The name of the APR_RING_ENTRY in the element struct
182 */
183#define APR_RING_PREV(ep, link) (ep)->link.prev
184
185
186/**
187 * Initialize a ring
188 * @param hp The head of the ring
189 * @param elem The name of the element struct
190 * @param link The name of the APR_RING_ENTRY in the element struct
191 */
192#define APR_RING_INIT(hp, elem, link) do { \
193 APR_RING_FIRST((hp)) = APR_RING_SENTINEL((hp), elem, link); \
194 APR_RING_LAST((hp)) = APR_RING_SENTINEL((hp), elem, link); \
195 } while (0)
196
197/**
198 * Determine if a ring is empty
199 * @param hp The head of the ring
200 * @param elem The name of the element struct
201 * @param link The name of the APR_RING_ENTRY in the element struct
202 * @return true or false
203 */
204#define APR_RING_EMPTY(hp, elem, link) \
205 (APR_RING_FIRST((hp)) == APR_RING_SENTINEL((hp), elem, link))
206
207/**
208 * Initialize a singleton element
209 * @param ep The element
210 * @param link The name of the APR_RING_ENTRY in the element struct
211 */
212#define APR_RING_ELEM_INIT(ep, link) do { \
213 APR_RING_NEXT((ep), link) = (ep); \
214 APR_RING_PREV((ep), link) = (ep); \
215 } while (0)
216
217
218/**
219 * Splice the sequence ep1..epN into the ring before element lep
220 * (..lep.. becomes ..ep1..epN..lep..)
221 * @warning This doesn't work for splicing before the first element or on
222 * empty rings... see APR_RING_SPLICE_HEAD for one that does
223 * @param lep Element in the ring to splice before
224 * @param ep1 First element in the sequence to splice in
225 * @param epN Last element in the sequence to splice in
226 * @param link The name of the APR_RING_ENTRY in the element struct
227 */
228#define APR_RING_SPLICE_BEFORE(lep, ep1, epN, link) do { \
229 APR_RING_NEXT((epN), link) = (lep); \
230 APR_RING_PREV((ep1), link) = APR_RING_PREV((lep), link); \
231 APR_RING_NEXT(APR_RING_PREV((lep), link), link) = (ep1); \
232 APR_RING_PREV((lep), link) = (epN); \
233 } while (0)
234
235/**
236 * Splice the sequence ep1..epN into the ring after element lep
237 * (..lep.. becomes ..lep..ep1..epN..)
238 * @warning This doesn't work for splicing after the last element or on
239 * empty rings... see APR_RING_SPLICE_TAIL for one that does
240 * @param lep Element in the ring to splice after
241 * @param ep1 First element in the sequence to splice in
242 * @param epN Last element in the sequence to splice in
243 * @param link The name of the APR_RING_ENTRY in the element struct
244 */
245#define APR_RING_SPLICE_AFTER(lep, ep1, epN, link) do { \
246 APR_RING_PREV((ep1), link) = (lep); \
247 APR_RING_NEXT((epN), link) = APR_RING_NEXT((lep), link); \
248 APR_RING_PREV(APR_RING_NEXT((lep), link), link) = (epN); \
249 APR_RING_NEXT((lep), link) = (ep1); \
250 } while (0)
251
252/**
253 * Insert the element nep into the ring before element lep
254 * (..lep.. becomes ..nep..lep..)
255 * @warning This doesn't work for inserting before the first element or on
256 * empty rings... see APR_RING_INSERT_HEAD for one that does
257 * @param lep Element in the ring to insert before
258 * @param nep Element to insert
259 * @param link The name of the APR_RING_ENTRY in the element struct
260 */
261#define APR_RING_INSERT_BEFORE(lep, nep, link) \
262 APR_RING_SPLICE_BEFORE((lep), (nep), (nep), link)
263
264/**
265 * Insert the element nep into the ring after element lep
266 * (..lep.. becomes ..lep..nep..)
267 * @warning This doesn't work for inserting after the last element or on
268 * empty rings... see APR_RING_INSERT_TAIL for one that does
269 * @param lep Element in the ring to insert after
270 * @param nep Element to insert
271 * @param link The name of the APR_RING_ENTRY in the element struct
272 */
273#define APR_RING_INSERT_AFTER(lep, nep, link) \
274 APR_RING_SPLICE_AFTER((lep), (nep), (nep), link)
275
276
277/**
278 * Splice the sequence ep1..epN into the ring before the first element
279 * (..hp.. becomes ..hp..ep1..epN..)
280 * @param hp Head of the ring
281 * @param ep1 First element in the sequence to splice in
282 * @param epN Last element in the sequence to splice in
283 * @param elem The name of the element struct
284 * @param link The name of the APR_RING_ENTRY in the element struct
285 */
286#define APR_RING_SPLICE_HEAD(hp, ep1, epN, elem, link) do { \
287 APR_RING_PREV((ep1), link) = APR_RING_SENTINEL((hp), elem, link);\
288 APR_RING_NEXT((epN), link) = APR_RING_FIRST((hp)); \
289 APR_RING_PREV(APR_RING_FIRST((hp)), link) = (epN); \
290 APR_RING_FIRST((hp)) = (ep1); \
291 } while (0)
292
293/**
294 * Splice the sequence ep1..epN into the ring after the last element
295 * (..hp.. becomes ..ep1..epN..hp..)
296 * @param hp Head of the ring
297 * @param ep1 First element in the sequence to splice in
298 * @param epN Last element in the sequence to splice in
299 * @param elem The name of the element struct
300 * @param link The name of the APR_RING_ENTRY in the element struct
301 */
302#define APR_RING_SPLICE_TAIL(hp, ep1, epN, elem, link) do { \
303 APR_RING_NEXT((epN), link) = APR_RING_SENTINEL((hp), elem, link);\
304 APR_RING_PREV((ep1), link) = APR_RING_LAST((hp)); \
305 APR_RING_NEXT(APR_RING_LAST((hp)), link) = (ep1); \
306 APR_RING_LAST((hp)) = (epN); \
307 } while (0)
308
309/**
310 * Insert the element nep into the ring before the first element
311 * (..hp.. becomes ..hp..nep..)
312 * @param hp Head of the ring
313 * @param nep Element to insert
314 * @param elem The name of the element struct
315 * @param link The name of the APR_RING_ENTRY in the element struct
316 */
317#define APR_RING_INSERT_HEAD(hp, nep, elem, link) \
318 APR_RING_SPLICE_HEAD((hp), (nep), (nep), elem, link)
319
320/**
321 * Insert the element nep into the ring after the last element
322 * (..hp.. becomes ..nep..hp..)
323 * @param hp Head of the ring
324 * @param nep Element to insert
325 * @param elem The name of the element struct
326 * @param link The name of the APR_RING_ENTRY in the element struct
327 */
328#define APR_RING_INSERT_TAIL(hp, nep, elem, link) \
329 APR_RING_SPLICE_TAIL((hp), (nep), (nep), elem, link)
330
331/**
332 * Concatenate ring h2 onto the end of ring h1, leaving h2 empty.
333 * @param h1 Head of the ring to concatenate onto
334 * @param h2 Head of the ring to concatenate
335 * @param elem The name of the element struct
336 * @param link The name of the APR_RING_ENTRY in the element struct
337 */
338#define APR_RING_CONCAT(h1, h2, elem, link) do { \
339 if (!APR_RING_EMPTY((h2), elem, link)) { \
340 APR_RING_SPLICE_TAIL((h1), APR_RING_FIRST((h2)), \
341 APR_RING_LAST((h2)), elem, link); \
342 APR_RING_INIT((h2), elem, link); \
343 } \
344 } while (0)
345
346/**
347 * Prepend ring h2 onto the beginning of ring h1, leaving h2 empty.
348 * @param h1 Head of the ring to prepend onto
349 * @param h2 Head of the ring to prepend
350 * @param elem The name of the element struct
351 * @param link The name of the APR_RING_ENTRY in the element struct
352 */
353#define APR_RING_PREPEND(h1, h2, elem, link) do { \
354 if (!APR_RING_EMPTY((h2), elem, link)) { \
355 APR_RING_SPLICE_HEAD((h1), APR_RING_FIRST((h2)), \
356 APR_RING_LAST((h2)), elem, link); \
357 APR_RING_INIT((h2), elem, link); \
358 } \
359 } while (0)
360
361/**
362 * Unsplice a sequence of elements from a ring
363 * @warning The unspliced sequence is left with dangling pointers at either end
364 * @param ep1 First element in the sequence to unsplice
365 * @param epN Last element in the sequence to unsplice
366 * @param link The name of the APR_RING_ENTRY in the element struct
367 */
368#define APR_RING_UNSPLICE(ep1, epN, link) do { \
369 APR_RING_NEXT(APR_RING_PREV((ep1), link), link) = \
370 APR_RING_NEXT((epN), link); \
371 APR_RING_PREV(APR_RING_NEXT((epN), link), link) = \
372 APR_RING_PREV((ep1), link); \
373 } while (0)
374
375/**
376 * Remove a single element from a ring
377 * @warning The unspliced element is left with dangling pointers at either end
378 * @param ep Element to remove
379 * @param link The name of the APR_RING_ENTRY in the element struct
380 */
381#define APR_RING_REMOVE(ep, link) \
382 APR_RING_UNSPLICE((ep), (ep), link)
383
384/**
385 * Iterate over a ring
386 * @param ep The current element
387 * @param head The head of the ring
388 * @param elem The name of the element struct
389 * @param link The name of the APR_RING_ENTRY in the element struct
390 */
391#define APR_RING_FOREACH(ep, head, elem, link) \
392 for (ep = APR_RING_FIRST(head); \
393 ep != APR_RING_SENTINEL(head, elem, link); \
394 ep = APR_RING_NEXT(ep, link))
395
396/**
397 * Iterate over a ring safe against removal of the current element
398 * @param ep1 The current element
399 * @param ep2 Iteration cursor
400 * @param head The head of the ring
401 * @param elem The name of the element struct
402 * @param link The name of the APR_RING_ENTRY in the element struct
403 */
404#define APR_RING_FOREACH_SAFE(ep1, ep2, head, elem, link) \
405 for (ep1 = APR_RING_FIRST(head), ep2 = APR_RING_NEXT(ep1, link); \
406 ep1 != APR_RING_SENTINEL(head, elem, link); \
407 ep1 = ep2, ep2 = APR_RING_NEXT(ep1, link))
408
409/* Debugging tools: */
410
411#ifdef APR_RING_DEBUG
412#include <stdio.h>
413#include <assert.h>
414
415#define APR_RING_CHECK_ONE(msg, ptr) \
416 fprintf(stderr, "*** %s %p\n", msg, ptr)
417
418#define APR_RING_CHECK(hp, elem, link, msg) \
419 APR_RING_CHECK_ELEM(APR_RING_SENTINEL(hp, elem, link), elem, link, msg)
420
421#define APR_RING_CHECK_ELEM(ep, elem, link, msg) do { \
422 struct elem *start = (ep); \
423 struct elem *here = start; \
424 fprintf(stderr, "*** ring check start -- %s\n", msg); \
425 do { \
426 fprintf(stderr, "\telem %p\n", here); \
427 fprintf(stderr, "\telem->next %p\n", \
428 APR_RING_NEXT(here, link)); \
429 fprintf(stderr, "\telem->prev %p\n", \
430 APR_RING_PREV(here, link)); \
431 fprintf(stderr, "\telem->next->prev %p\n", \
432 APR_RING_PREV(APR_RING_NEXT(here, link), link)); \
433 fprintf(stderr, "\telem->prev->next %p\n", \
434 APR_RING_NEXT(APR_RING_PREV(here, link), link)); \
435 if (APR_RING_PREV(APR_RING_NEXT(here, link), link) != here) { \
436 fprintf(stderr, "\t*** elem->next->prev != elem\n"); \
437 break; \
438 } \
439 if (APR_RING_NEXT(APR_RING_PREV(here, link), link) != here) { \
440 fprintf(stderr, "\t*** elem->prev->next != elem\n"); \
441 break; \
442 } \
443 here = APR_RING_NEXT(here, link); \
444 } while (here != start); \
445 fprintf(stderr, "*** ring check end\n"); \
446 } while (0)
447
448#define APR_RING_CHECK_CONSISTENCY(hp, elem, link) \
449 APR_RING_CHECK_ELEM_CONSISTENCY(APR_RING_SENTINEL(hp, elem, link),\
450 elem, link)
451
452#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link) do { \
453 struct elem *start = (ep); \
454 struct elem *here = start; \
455 do { \
456 assert(APR_RING_PREV(APR_RING_NEXT(here, link), link) == here); \
457 assert(APR_RING_NEXT(APR_RING_PREV(here, link), link) == here); \
458 here = APR_RING_NEXT(here, link); \
459 } while (here != start); \
460 } while (0)
461
462#else
463/**
464 * Print a single pointer value to STDERR
465 * (This is a no-op unless APR_RING_DEBUG is defined.)
466 * @param msg Descriptive message
467 * @param ptr Pointer value to print
468 */
469#define APR_RING_CHECK_ONE(msg, ptr)
470/**
471 * Dump all ring pointers to STDERR, starting with the head and looping all
472 * the way around the ring back to the head. Aborts if an inconsistency
473 * is found.
474 * (This is a no-op unless APR_RING_DEBUG is defined.)
475 * @param hp Head of the ring
476 * @param elem The name of the element struct
477 * @param link The name of the APR_RING_ENTRY in the element struct
478 * @param msg Descriptive message
479 */
480#define APR_RING_CHECK(hp, elem, link, msg)
481/**
482 * Loops around a ring and checks all the pointers for consistency. Pops
483 * an assertion if any inconsistency is found. Same idea as APR_RING_CHECK()
484 * except that it's silent if all is well.
485 * (This is a no-op unless APR_RING_DEBUG is defined.)
486 * @param hp Head of the ring
487 * @param elem The name of the element struct
488 * @param link The name of the APR_RING_ENTRY in the element struct
489 */
490#define APR_RING_CHECK_CONSISTENCY(hp, elem, link)
491/**
492 * Dump all ring pointers to STDERR, starting with the given element and
493 * looping all the way around the ring back to that element. Aborts if
494 * an inconsistency is found.
495 * (This is a no-op unless APR_RING_DEBUG is defined.)
496 * @param ep The element
497 * @param elem The name of the element struct
498 * @param link The name of the APR_RING_ENTRY in the element struct
499 * @param msg Descriptive message
500 */
501#define APR_RING_CHECK_ELEM(ep, elem, link, msg)
502/**
503 * Loops around a ring, starting with the given element, and checks all
504 * the pointers for consistency. Pops an assertion if any inconsistency
505 * is found. Same idea as APR_RING_CHECK_ELEM() except that it's silent
506 * if all is well.
507 * (This is a no-op unless APR_RING_DEBUG is defined.)
508 * @param ep The element
509 * @param elem The name of the element struct
510 * @param link The name of the APR_RING_ENTRY in the element struct
511 */
512#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link)
513#endif
514
515/** @} */
516
517#endif /* !APR_RING_H */
apr_general.h
APR Miscellaneous library routines.