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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
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/>
23 * We'd use Dean's code directly if we could guarantee the
24 * availability of inline functions.
38 #include "apr_general.h"
41 * @defgroup apr_ring Ring Macro Implementations
43 * A ring is a kind of doubly-linked list that can be manipulated
44 * without knowing where its head is.
51 * A ring element struct is linked to the other elements in the ring
52 * through its ring entry field, e.g.
54 * struct my_element_t {
55 * APR_RING_ENTRY(my_element_t) link;
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.
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.
70 #define APR_RING_ENTRY(elem) \
72 struct elem * volatile next; \
73 struct elem * volatile prev; \
79 * Each ring is managed via its head, which is a struct declared like this:
81 * APR_RING_HEAD(my_ring_t, my_element_t);
82 * struct my_ring_t ring, *ringp;
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.
88 * The first element in the ring is next after the head, and the last
89 * element is just before the head.
91 #define APR_RING_HEAD(head, elem) \
93 struct elem * volatile next; \
94 struct elem * volatile prev; \
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.
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.
111 * +->+------+<-+ +->+------+<-+ +->+------+<-+
112 * | |struct| | | |struct| | | |struct| |
113 * / | elem | \/ | elem | \/ | elem | \
114 * ... | | /\ | | /\ | | ...
115 * +------+ | | +------+ | | +------+
116 * ...--|prev | | +--|ring | | +--|prev |
117 * | next|--+ | entry|--+ | next|--...
118 * +------+ +------+ +------+
119 * | etc. | | etc. | | etc. |
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.
133 * +->+------+<-+ +->sentinel<-+ +->+------+<-+
134 * | |struct| | | | | |struct| |
135 * / | elem | \/ \/ | elem | \
136 * ... | | /\ /\ | | ...
137 * +------+ | | +------+ | | +------+
138 * ...--|prev | | +--|ring | | +--|prev |
139 * | next|--+ | head|--+ | next|--...
140 * +------+ +------+ +------+
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.
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.
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
159 #define APR_RING_SENTINEL(hp, elem, link) \
160 (struct elem *)((char *)(&(hp)->next) - APR_OFFSETOF(struct elem, link))
163 * The first element of the ring
164 * @param hp The head of the ring
166 #define APR_RING_FIRST(hp) (hp)->next
168 * The last element of the ring
169 * @param hp The head of the ring
171 #define APR_RING_LAST(hp) (hp)->prev
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
177 #define APR_RING_NEXT(ep, link) (ep)->link.next
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
183 #define APR_RING_PREV(ep, link) (ep)->link.prev
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
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); \
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
204 #define APR_RING_EMPTY(hp, elem, link) \
205 (APR_RING_FIRST((hp)) == APR_RING_SENTINEL((hp), elem, link))
208 * Initialize a singleton element
209 * @param ep The element
210 * @param link The name of the APR_RING_ENTRY in the element struct
212 #define APR_RING_ELEM_INIT(ep, link) do { \
213 APR_RING_NEXT((ep), link) = (ep); \
214 APR_RING_PREV((ep), link) = (ep); \
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
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); \
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
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); \
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
261 #define APR_RING_INSERT_BEFORE(lep, nep, link) \
262 APR_RING_SPLICE_BEFORE((lep), (nep), (nep), link)
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
273 #define APR_RING_INSERT_AFTER(lep, nep, link) \
274 APR_RING_SPLICE_AFTER((lep), (nep), (nep), link)
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
286 #define APR_RING_SPLICE_HEAD(hp, ep1, epN, elem, link) \
287 APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((hp), elem, link), \
291 * Splice the sequence ep1..epN into the ring after the last element
292 * (..hp.. becomes ..ep1..epN..hp..)
293 * @param hp Head of the ring
294 * @param ep1 First element in the sequence to splice in
295 * @param epN Last element in the sequence to splice in
296 * @param elem The name of the element struct
297 * @param link The name of the APR_RING_ENTRY in the element struct
299 #define APR_RING_SPLICE_TAIL(hp, ep1, epN, elem, link) \
300 APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((hp), elem, link), \
304 * Insert the element nep into the ring before the first element
305 * (..hp.. becomes ..hp..nep..)
306 * @param hp Head of the ring
307 * @param nep Element to insert
308 * @param elem The name of the element struct
309 * @param link The name of the APR_RING_ENTRY in the element struct
311 #define APR_RING_INSERT_HEAD(hp, nep, elem, link) \
312 APR_RING_SPLICE_HEAD((hp), (nep), (nep), elem, link)
315 * Insert the element nep into the ring after the last element
316 * (..hp.. becomes ..nep..hp..)
317 * @param hp Head of the ring
318 * @param nep Element to insert
319 * @param elem The name of the element struct
320 * @param link The name of the APR_RING_ENTRY in the element struct
322 #define APR_RING_INSERT_TAIL(hp, nep, elem, link) \
323 APR_RING_SPLICE_TAIL((hp), (nep), (nep), elem, link)
326 * Concatenate ring h2 onto the end of ring h1, leaving h2 empty.
327 * @param h1 Head of the ring to concatenate onto
328 * @param h2 Head of the ring to concatenate
329 * @param elem The name of the element struct
330 * @param link The name of the APR_RING_ENTRY in the element struct
332 #define APR_RING_CONCAT(h1, h2, elem, link) do { \
333 if (!APR_RING_EMPTY((h2), elem, link)) { \
334 APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((h1), elem, link), \
335 APR_RING_FIRST((h2)), \
336 APR_RING_LAST((h2)), link); \
337 APR_RING_INIT((h2), elem, link); \
342 * Prepend ring h2 onto the beginning of ring h1, leaving h2 empty.
343 * @param h1 Head of the ring to prepend onto
344 * @param h2 Head of the ring to prepend
345 * @param elem The name of the element struct
346 * @param link The name of the APR_RING_ENTRY in the element struct
348 #define APR_RING_PREPEND(h1, h2, elem, link) do { \
349 if (!APR_RING_EMPTY((h2), elem, link)) { \
350 APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((h1), elem, link), \
351 APR_RING_FIRST((h2)), \
352 APR_RING_LAST((h2)), link); \
353 APR_RING_INIT((h2), elem, link); \
358 * Unsplice a sequence of elements from a ring
359 * @warning The unspliced sequence is left with dangling pointers at either end
360 * @param ep1 First element in the sequence to unsplice
361 * @param epN Last element in the sequence to unsplice
362 * @param link The name of the APR_RING_ENTRY in the element struct
364 #define APR_RING_UNSPLICE(ep1, epN, link) do { \
365 APR_RING_NEXT(APR_RING_PREV((ep1), link), link) = \
366 APR_RING_NEXT((epN), link); \
367 APR_RING_PREV(APR_RING_NEXT((epN), link), link) = \
368 APR_RING_PREV((ep1), link); \
372 * Remove a single element from a ring
373 * @warning The unspliced element is left with dangling pointers at either end
374 * @param ep Element to remove
375 * @param link The name of the APR_RING_ENTRY in the element struct
377 #define APR_RING_REMOVE(ep, link) \
378 APR_RING_UNSPLICE((ep), (ep), link)
381 * Iterate over a ring
382 * @param ep The current element
383 * @param head The head of the ring
384 * @param elem The name of the element struct
385 * @param link The name of the APR_RING_ENTRY in the element struct
387 #define APR_RING_FOREACH(ep, head, elem, link) \
388 for (ep = APR_RING_FIRST(head); \
389 ep != APR_RING_SENTINEL(head, elem, link); \
390 ep = APR_RING_NEXT(ep, link))
393 * Iterate over a ring safe against removal of the current element
394 * @param ep1 The current element
395 * @param ep2 Iteration cursor
396 * @param head The head of the ring
397 * @param elem The name of the element struct
398 * @param link The name of the APR_RING_ENTRY in the element struct
400 #define APR_RING_FOREACH_SAFE(ep1, ep2, head, elem, link) \
401 for (ep1 = APR_RING_FIRST(head), ep2 = APR_RING_NEXT(ep1, link); \
402 ep1 != APR_RING_SENTINEL(head, elem, link); \
403 ep1 = ep2, ep2 = APR_RING_NEXT(ep1, link))
405 /* Debugging tools: */
407 #ifdef APR_RING_DEBUG
411 #define APR_RING_CHECK_ONE(msg, ptr) \
412 fprintf(stderr, "*** %s %p\n", msg, ptr)
414 #define APR_RING_CHECK(hp, elem, link, msg) \
415 APR_RING_CHECK_ELEM(APR_RING_SENTINEL(hp, elem, link), elem, link, msg)
417 #define APR_RING_CHECK_ELEM(ep, elem, link, msg) do { \
418 struct elem *start = (ep); \
419 struct elem *here = start; \
420 fprintf(stderr, "*** ring check start -- %s\n", msg); \
422 fprintf(stderr, "\telem %p\n", here); \
423 fprintf(stderr, "\telem->next %p\n", \
424 APR_RING_NEXT(here, link)); \
425 fprintf(stderr, "\telem->prev %p\n", \
426 APR_RING_PREV(here, link)); \
427 fprintf(stderr, "\telem->next->prev %p\n", \
428 APR_RING_PREV(APR_RING_NEXT(here, link), link)); \
429 fprintf(stderr, "\telem->prev->next %p\n", \
430 APR_RING_NEXT(APR_RING_PREV(here, link), link)); \
431 if (APR_RING_PREV(APR_RING_NEXT(here, link), link) != here) { \
432 fprintf(stderr, "\t*** elem->next->prev != elem\n"); \
435 if (APR_RING_NEXT(APR_RING_PREV(here, link), link) != here) { \
436 fprintf(stderr, "\t*** elem->prev->next != elem\n"); \
439 here = APR_RING_NEXT(here, link); \
440 } while (here != start); \
441 fprintf(stderr, "*** ring check end\n"); \
444 #define APR_RING_CHECK_CONSISTENCY(hp, elem, link) \
445 APR_RING_CHECK_ELEM_CONSISTENCY(APR_RING_SENTINEL(hp, elem, link),\
448 #define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link) do { \
449 struct elem *start = (ep); \
450 struct elem *here = start; \
452 assert(APR_RING_PREV(APR_RING_NEXT(here, link), link) == here); \
453 assert(APR_RING_NEXT(APR_RING_PREV(here, link), link) == here); \
454 here = APR_RING_NEXT(here, link); \
455 } while (here != start); \
460 * Print a single pointer value to STDERR
461 * (This is a no-op unless APR_RING_DEBUG is defined.)
462 * @param msg Descriptive message
463 * @param ptr Pointer value to print
465 #define APR_RING_CHECK_ONE(msg, ptr)
467 * Dump all ring pointers to STDERR, starting with the head and looping all
468 * the way around the ring back to the head. Aborts if an inconsistency
470 * (This is a no-op unless APR_RING_DEBUG is defined.)
471 * @param hp Head of the ring
472 * @param elem The name of the element struct
473 * @param link The name of the APR_RING_ENTRY in the element struct
474 * @param msg Descriptive message
476 #define APR_RING_CHECK(hp, elem, link, msg)
478 * Loops around a ring and checks all the pointers for consistency. Pops
479 * an assertion if any inconsistency is found. Same idea as APR_RING_CHECK()
480 * except that it's silent if all is well.
481 * (This is a no-op unless APR_RING_DEBUG is defined.)
482 * @param hp Head of the ring
483 * @param elem The name of the element struct
484 * @param link The name of the APR_RING_ENTRY in the element struct
486 #define APR_RING_CHECK_CONSISTENCY(hp, elem, link)
488 * Dump all ring pointers to STDERR, starting with the given element and
489 * looping all the way around the ring back to that element. Aborts if
490 * an inconsistency is found.
491 * (This is a no-op unless APR_RING_DEBUG is defined.)
492 * @param ep The element
493 * @param elem The name of the element struct
494 * @param link The name of the APR_RING_ENTRY in the element struct
495 * @param msg Descriptive message
497 #define APR_RING_CHECK_ELEM(ep, elem, link, msg)
499 * Loops around a ring, starting with the given element, and checks all
500 * the pointers for consistency. Pops an assertion if any inconsistency
501 * is found. Same idea as APR_RING_CHECK_ELEM() except that it's silent
503 * (This is a no-op unless APR_RING_DEBUG is defined.)
504 * @param ep The element
505 * @param elem The name of the element struct
506 * @param link The name of the APR_RING_ENTRY in the element struct
508 #define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link)
513 #endif /* !APR_RING_H */