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queue.h
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1 /* $OpenBSD: queue.h,v 1.32 2007/04/30 18:42:34 pedro Exp $ */
2 /* $NetBSD: queue.h,v 1.11 1996/05/16 05:17:14 mycroft Exp $ */
3 
4 /*
5  * Copyright (c) 1991, 1993
6  * The Regents of the University of California. All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  * notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  * notice, this list of conditions and the following disclaimer in the
15  * documentation and/or other materials provided with the distribution.
16  * 3. Neither the name of the University nor the names of its contributors
17  * may be used to endorse or promote products derived from this software
18  * without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30  * SUCH DAMAGE.
31  *
32  * @(#)queue.h 8.5 (Berkeley) 8/20/94
33  */
34 
35 #ifndef _SYS_QUEUE_H_
36 #define _SYS_QUEUE_H_
37 
38 /*
39  * This file defines five types of data structures: singly-linked lists,
40  * lists, simple queues, tail queues, and circular queues.
41  *
42  *
43  * A singly-linked list is headed by a single forward pointer. The elements
44  * are singly linked for minimum space and pointer manipulation overhead at
45  * the expense of O(n) removal for arbitrary elements. New elements can be
46  * added to the list after an existing element or at the head of the list.
47  * Elements being removed from the head of the list should use the explicit
48  * macro for this purpose for optimum efficiency. A singly-linked list may
49  * only be traversed in the forward direction. Singly-linked lists are ideal
50  * for applications with large datasets and few or no removals or for
51  * implementing a LIFO queue.
52  *
53  * A list is headed by a single forward pointer (or an array of forward
54  * pointers for a hash table header). The elements are doubly linked
55  * so that an arbitrary element can be removed without a need to
56  * traverse the list. New elements can be added to the list before
57  * or after an existing element or at the head of the list. A list
58  * may only be traversed in the forward direction.
59  *
60  * A simple queue is headed by a pair of pointers, one the head of the
61  * list and the other to the tail of the list. The elements are singly
62  * linked to save space, so elements can only be removed from the
63  * head of the list. New elements can be added to the list before or after
64  * an existing element, at the head of the list, or at the end of the
65  * list. A simple queue may only be traversed in the forward direction.
66  *
67  * A tail queue is headed by a pair of pointers, one to the head of the
68  * list and the other to the tail of the list. The elements are doubly
69  * linked so that an arbitrary element can be removed without a need to
70  * traverse the list. New elements can be added to the list before or
71  * after an existing element, at the head of the list, or at the end of
72  * the list. A tail queue may be traversed in either direction.
73  *
74  * A circle queue is headed by a pair of pointers, one to the head of the
75  * list and the other to the tail of the list. The elements are doubly
76  * linked so that an arbitrary element can be removed without a need to
77  * traverse the list. New elements can be added to the list before or after
78  * an existing element, at the head of the list, or at the end of the list.
79  * A circle queue may be traversed in either direction, but has a more
80  * complex end of list detection.
81  *
82  * For details on the use of these macros, see the queue(3) manual page.
83  */
84 
85 #if defined(__clang_analyzer__) || defined(QUEUE_MACRO_DEBUG) || (defined(_KERNEL) && defined(DIAGNOSTIC))
86 #define _Q_INVALIDATE(a) ((a) = ((void *)-1))
87 #else
88 #define _Q_INVALIDATE(a)
89 #endif
90 
91 #if defined(__clang_analyzer__)
92 #define _Q_ASSERT(a) assert((a))
93 #else
94 #define _Q_ASSERT(a)
95 #endif
96 
97 /*
98  * Singly-linked List definitions.
99  */
100 
101 /*
102  * The following macros are not used and are in conflict with Win32 API
103  */
104 
105 #if 0
106 
107 #define SLIST_HEAD(name, type) \
108 struct name { \
109  struct type *slh_first; /* first element */ \
110 }
111 
112 #define SLIST_HEAD_INITIALIZER(head) \
113  { NULL }
114 
115 #define SLIST_ENTRY(type) \
116 struct { \
117  struct type *sle_next; /* next element */ \
118 }
119 
120 /*
121  * Singly-linked List access methods.
122  */
123 #define SLIST_FIRST(head) ((head)->slh_first)
124 #define SLIST_END(head) NULL
125 #define SLIST_EMPTY(head) (SLIST_FIRST(head) == SLIST_END(head))
126 #define SLIST_NEXT(elm, field) ((elm)->field.sle_next)
127 
128 #define SLIST_FOREACH(var, head, field) \
129  for((var) = SLIST_FIRST(head); \
130  (var) != SLIST_END(head); \
131  (var) = SLIST_NEXT(var, field))
132 
133 #define SLIST_FOREACH_PREVPTR(var, varp, head, field) \
134  for ((varp) = &SLIST_FIRST((head)); \
135  ((var) = *(varp)) != SLIST_END(head); \
136  (varp) = &SLIST_NEXT((var), field))
137 
138 /*
139  * Singly-linked List functions.
140  */
141 #define SLIST_INIT(head) { \
142  SLIST_FIRST(head) = SLIST_END(head); \
143 }
144 
145 #define SLIST_INSERT_AFTER(slistelm, elm, field) do { \
146  (elm)->field.sle_next = (slistelm)->field.sle_next; \
147  (slistelm)->field.sle_next = (elm); \
148 } while (0)
149 
150 #define SLIST_INSERT_HEAD(head, elm, field) do { \
151  (elm)->field.sle_next = (head)->slh_first; \
152  (head)->slh_first = (elm); \
153 } while (0)
154 
155 #define SLIST_REMOVE_NEXT(head, elm, field) do { \
156  (elm)->field.sle_next = (elm)->field.sle_next->field.sle_next; \
157 } while (0)
158 
159 #define SLIST_REMOVE_HEAD(head, field) do { \
160  (head)->slh_first = (head)->slh_first->field.sle_next; \
161 } while (0)
162 
163 #define SLIST_REMOVE(head, elm, type, field) do { \
164  if ((head)->slh_first == (elm)) { \
165  SLIST_REMOVE_HEAD((head), field); \
166  } else { \
167  struct type *curelm = (head)->slh_first; \
168  \
169  while (curelm->field.sle_next != (elm)) \
170  curelm = curelm->field.sle_next; \
171  curelm->field.sle_next = \
172  curelm->field.sle_next->field.sle_next; \
173  _Q_INVALIDATE((elm)->field.sle_next); \
174  } \
175 } while (0)
176 
177 #endif /* 0 */
178 
179 /*
180  * List definitions.
181  */
182 #define LIST_HEAD(name, type) \
183 struct name { \
184  struct type *lh_first; /* first element */ \
185 }
186 
187 #define LIST_HEAD_INITIALIZER(head) \
188  { NULL }
189 
190 #define LIST_ENTRY(type) \
191 struct { \
192  struct type *le_next; /* next element */ \
193  struct type **le_prev; /* address of previous next element */ \
194 }
195 
196 /*
197  * List access methods
198  */
199 #define LIST_FIRST(head) ((head)->lh_first)
200 #define LIST_END(head) NULL
201 #define LIST_EMPTY(head) (LIST_FIRST(head) == LIST_END(head))
202 #define LIST_NEXT(elm, field) ((elm)->field.le_next)
203 
204 #define LIST_FOREACH(var, head, field) \
205  for((var) = LIST_FIRST(head); \
206  (var)!= LIST_END(head); \
207  (var) = LIST_NEXT(var, field))
208 
209 /*
210  * List functions.
211  */
212 #define LIST_INIT(head) do { \
213  LIST_FIRST(head) = LIST_END(head); \
214 } while (0)
215 
216 #define LIST_INSERT_AFTER(listelm, elm, field) do { \
217  if (((elm)->field.le_next = (listelm)->field.le_next) != NULL) \
218  (listelm)->field.le_next->field.le_prev = \
219  &(elm)->field.le_next; \
220  (listelm)->field.le_next = (elm); \
221  (elm)->field.le_prev = &(listelm)->field.le_next; \
222 } while (0)
223 
224 #define LIST_INSERT_BEFORE(listelm, elm, field) do { \
225  (elm)->field.le_prev = (listelm)->field.le_prev; \
226  (elm)->field.le_next = (listelm); \
227  *(listelm)->field.le_prev = (elm); \
228  (listelm)->field.le_prev = &(elm)->field.le_next; \
229 } while (0)
230 
231 #define LIST_INSERT_HEAD(head, elm, field) do { \
232  if (((elm)->field.le_next = (head)->lh_first) != NULL) \
233  (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
234  (head)->lh_first = (elm); \
235  (elm)->field.le_prev = &(head)->lh_first; \
236 } while (0)
237 
238 #define LIST_REMOVE(elm, field) do { \
239  if ((elm)->field.le_next != NULL) \
240  (elm)->field.le_next->field.le_prev = \
241  (elm)->field.le_prev; \
242  *(elm)->field.le_prev = (elm)->field.le_next; \
243  _Q_INVALIDATE((elm)->field.le_prev); \
244  _Q_INVALIDATE((elm)->field.le_next); \
245 } while (0)
246 
247 #define LIST_REPLACE(elm, elm2, field) do { \
248  if (((elm2)->field.le_next = (elm)->field.le_next) != NULL) \
249  (elm2)->field.le_next->field.le_prev = \
250  &(elm2)->field.le_next; \
251  (elm2)->field.le_prev = (elm)->field.le_prev; \
252  *(elm2)->field.le_prev = (elm2); \
253  _Q_INVALIDATE((elm)->field.le_prev); \
254  _Q_INVALIDATE((elm)->field.le_next); \
255 } while (0)
256 
257 /*
258  * Simple queue definitions.
259  */
260 #define SIMPLEQ_HEAD(name, type) \
261 struct name { \
262  struct type *sqh_first; /* first element */ \
263  struct type **sqh_last; /* addr of last next element */ \
264 }
265 
266 #define SIMPLEQ_HEAD_INITIALIZER(head) \
267  { NULL, &(head).sqh_first }
268 
269 #define SIMPLEQ_ENTRY(type) \
270 struct { \
271  struct type *sqe_next; /* next element */ \
272 }
273 
274 /*
275  * Simple queue access methods.
276  */
277 #define SIMPLEQ_FIRST(head) ((head)->sqh_first)
278 #define SIMPLEQ_END(head) NULL
279 #define SIMPLEQ_EMPTY(head) (SIMPLEQ_FIRST(head) == SIMPLEQ_END(head))
280 #define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)
281 
282 #define SIMPLEQ_FOREACH(var, head, field) \
283  for((var) = SIMPLEQ_FIRST(head); \
284  (var) != SIMPLEQ_END(head); \
285  (var) = SIMPLEQ_NEXT(var, field))
286 
287 /*
288  * Simple queue functions.
289  */
290 #define SIMPLEQ_INIT(head) do { \
291  (head)->sqh_first = NULL; \
292  (head)->sqh_last = &(head)->sqh_first; \
293 } while (0)
294 
295 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do { \
296  if (((elm)->field.sqe_next = (head)->sqh_first) == NULL) \
297  (head)->sqh_last = &(elm)->field.sqe_next; \
298  (head)->sqh_first = (elm); \
299 } while (0)
300 
301 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do { \
302  (elm)->field.sqe_next = NULL; \
303  *(head)->sqh_last = (elm); \
304  (head)->sqh_last = &(elm)->field.sqe_next; \
305 } while (0)
306 
307 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \
308  if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
309  (head)->sqh_last = &(elm)->field.sqe_next; \
310  (listelm)->field.sqe_next = (elm); \
311 } while (0)
312 
313 #define SIMPLEQ_REMOVE_HEAD(head, field) do { \
314  if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
315  (head)->sqh_last = &(head)->sqh_first; \
316 } while (0)
317 
318 /*
319  * Tail queue definitions.
320  */
321 #define TAILQ_HEAD(name, type) \
322 struct name { \
323  struct type *tqh_first; /* first element */ \
324  struct type **tqh_last; /* addr of last next element */ \
325 }
326 
327 #define TAILQ_HEAD_INITIALIZER(head) \
328  { NULL, &(head).tqh_first }
329 
330 #define TAILQ_ENTRY(type) \
331 struct { \
332  struct type *tqe_next; /* next element */ \
333  struct type **tqe_prev; /* address of previous next element */ \
334 }
335 
336 /*
337  * tail queue access methods
338  */
339 #define TAILQ_FIRST(head) ((head)->tqh_first)
340 #define TAILQ_END(head) NULL
341 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
342 #define TAILQ_LAST(head, headname) \
343  (*(((struct headname *)((head)->tqh_last))->tqh_last))
344 /* XXX */
345 #define TAILQ_PREV(elm, headname, field) \
346  (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
347 #define TAILQ_EMPTY(head) \
348  (TAILQ_FIRST(head) == TAILQ_END(head))
349 
350 #define TAILQ_FOREACH(var, head, field) \
351  for((var) = TAILQ_FIRST(head); \
352  (var) != TAILQ_END(head); \
353  (var) = TAILQ_NEXT(var, field))
354 
355 /* removal safe iterator using a temprary element has last param */
356 #define TAILQ_FOREACH_SAFE(var, head, field, tvar) \
357  for((var) = TAILQ_FIRST(head), \
358  (tvar) = TAILQ_FIRST(head) ? TAILQ_NEXT(TAILQ_FIRST(head), field): NULL ; \
359  (var) != TAILQ_END(head); \
360  (var = tvar), (tvar) = var ? TAILQ_NEXT(var, field): NULL)
361 
362 #define TAILQ_FOREACH_REVERSE(var, head, headname, field) \
363  for((var) = TAILQ_LAST(head, headname); \
364  (var) != TAILQ_END(head); \
365  (var) = TAILQ_PREV(var, headname, field))
366 
367 /*
368  * Tail queue functions.
369  */
370 #define TAILQ_INIT(head) do { \
371  (head)->tqh_first = NULL; \
372  (head)->tqh_last = &(head)->tqh_first; \
373 } while (0)
374 
375 #define TAILQ_INSERT_HEAD(head, elm, field) do { \
376  if (((elm)->field.tqe_next = (head)->tqh_first) != NULL) \
377  (head)->tqh_first->field.tqe_prev = \
378  &(elm)->field.tqe_next; \
379  else \
380  (head)->tqh_last = &(elm)->field.tqe_next; \
381  (head)->tqh_first = (elm); \
382  (elm)->field.tqe_prev = &(head)->tqh_first; \
383 } while (0)
384 
385 #define TAILQ_INSERT_TAIL(head, elm, field) do { \
386  _Q_ASSERT((elm)); \
387  _Q_ASSERT((head)); \
388  (elm)->field.tqe_next = NULL; \
389  (elm)->field.tqe_prev = (head)->tqh_last; \
390  *(head)->tqh_last = (elm); \
391  _Q_ASSERT(*(head)->tqh_last); \
392  (head)->tqh_last = &(elm)->field.tqe_next; \
393 } while (0)
394 
395 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \
396  if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
397  (elm)->field.tqe_next->field.tqe_prev = \
398  &(elm)->field.tqe_next; \
399  else \
400  (head)->tqh_last = &(elm)->field.tqe_next; \
401  (listelm)->field.tqe_next = (elm); \
402  (elm)->field.tqe_prev = &(listelm)->field.tqe_next; \
403 } while (0)
404 
405 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do { \
406  (elm)->field.tqe_prev = (listelm)->field.tqe_prev; \
407  (elm)->field.tqe_next = (listelm); \
408  *(listelm)->field.tqe_prev = (elm); \
409  (listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
410 } while (0)
411 
412 #define TAILQ_REMOVE(head, elm, field) do { \
413  if (((elm)->field.tqe_next) != NULL) \
414  (elm)->field.tqe_next->field.tqe_prev = \
415  (elm)->field.tqe_prev; \
416  else \
417  (head)->tqh_last = (elm)->field.tqe_prev; \
418  *(elm)->field.tqe_prev = (elm)->field.tqe_next; \
419  _Q_ASSERT((head)->tqh_first != (elm)); \
420  _Q_INVALIDATE((elm)->field.tqe_prev); \
421  _Q_INVALIDATE((elm)->field.tqe_next); \
422 } while (0)
423 
424 #define TAILQ_REPLACE(head, elm, elm2, field) do { \
425  if (((elm2)->field.tqe_next = (elm)->field.tqe_next) != NULL) \
426  (elm2)->field.tqe_next->field.tqe_prev = \
427  &(elm2)->field.tqe_next; \
428  else \
429  (head)->tqh_last = &(elm2)->field.tqe_next; \
430  (elm2)->field.tqe_prev = (elm)->field.tqe_prev; \
431  *(elm2)->field.tqe_prev = (elm2); \
432  _Q_INVALIDATE((elm)->field.tqe_prev); \
433  _Q_INVALIDATE((elm)->field.tqe_next); \
434 } while (0)
435 
436 /*
437  * Circular queue definitions.
438  */
439 #define CIRCLEQ_HEAD(name, type) \
440 struct name { \
441  struct type *cqh_first; /* first element */ \
442  struct type *cqh_last; /* last element */ \
443 }
444 
445 #define CIRCLEQ_HEAD_INITIALIZER(head) \
446  { CIRCLEQ_END(&head), CIRCLEQ_END(&head) }
447 
448 #define CIRCLEQ_ENTRY(type) \
449 struct { \
450  struct type *cqe_next; /* next element */ \
451  struct type *cqe_prev; /* previous element */ \
452 }
453 
454 /*
455  * Circular queue access methods
456  */
457 #define CIRCLEQ_FIRST(head) ((head)->cqh_first)
458 #define CIRCLEQ_LAST(head) ((head)->cqh_last)
459 #define CIRCLEQ_END(head) ((void *)(head))
460 #define CIRCLEQ_NEXT(elm, field) ((elm)->field.cqe_next)
461 #define CIRCLEQ_PREV(elm, field) ((elm)->field.cqe_prev)
462 #define CIRCLEQ_EMPTY(head) \
463  (CIRCLEQ_FIRST(head) == CIRCLEQ_END(head))
464 
465 #define CIRCLEQ_FOREACH(var, head, field) \
466  for((var) = CIRCLEQ_FIRST(head); \
467  (var) != CIRCLEQ_END(head); \
468  (var) = CIRCLEQ_NEXT(var, field))
469 
470 #define CIRCLEQ_FOREACH_REVERSE(var, head, field) \
471  for((var) = CIRCLEQ_LAST(head); \
472  (var) != CIRCLEQ_END(head); \
473  (var) = CIRCLEQ_PREV(var, field))
474 
475 /*
476  * Circular queue functions.
477  */
478 #define CIRCLEQ_INIT(head) do { \
479  (head)->cqh_first = CIRCLEQ_END(head); \
480  (head)->cqh_last = CIRCLEQ_END(head); \
481 } while (0)
482 
483 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do { \
484  (elm)->field.cqe_next = (listelm)->field.cqe_next; \
485  (elm)->field.cqe_prev = (listelm); \
486  if ((listelm)->field.cqe_next == CIRCLEQ_END(head)) \
487  (head)->cqh_last = (elm); \
488  else \
489  (listelm)->field.cqe_next->field.cqe_prev = (elm); \
490  (listelm)->field.cqe_next = (elm); \
491 } while (0)
492 
493 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do { \
494  (elm)->field.cqe_next = (listelm); \
495  (elm)->field.cqe_prev = (listelm)->field.cqe_prev; \
496  if ((listelm)->field.cqe_prev == CIRCLEQ_END(head)) \
497  (head)->cqh_first = (elm); \
498  else \
499  (listelm)->field.cqe_prev->field.cqe_next = (elm); \
500  (listelm)->field.cqe_prev = (elm); \
501 } while (0)
502 
503 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do { \
504  (elm)->field.cqe_next = (head)->cqh_first; \
505  (elm)->field.cqe_prev = CIRCLEQ_END(head); \
506  if ((head)->cqh_last == CIRCLEQ_END(head)) \
507  (head)->cqh_last = (elm); \
508  else \
509  (head)->cqh_first->field.cqe_prev = (elm); \
510  (head)->cqh_first = (elm); \
511 } while (0)
512 
513 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do { \
514  (elm)->field.cqe_next = CIRCLEQ_END(head); \
515  (elm)->field.cqe_prev = (head)->cqh_last; \
516  if ((head)->cqh_first == CIRCLEQ_END(head)) \
517  (head)->cqh_first = (elm); \
518  else \
519  (head)->cqh_last->field.cqe_next = (elm); \
520  (head)->cqh_last = (elm); \
521 } while (0)
522 
523 #define CIRCLEQ_REMOVE(head, elm, field) do { \
524  if ((elm)->field.cqe_next == CIRCLEQ_END(head)) \
525  (head)->cqh_last = (elm)->field.cqe_prev; \
526  else \
527  (elm)->field.cqe_next->field.cqe_prev = \
528  (elm)->field.cqe_prev; \
529  if ((elm)->field.cqe_prev == CIRCLEQ_END(head)) \
530  (head)->cqh_first = (elm)->field.cqe_next; \
531  else \
532  (elm)->field.cqe_prev->field.cqe_next = \
533  (elm)->field.cqe_next; \
534  _Q_INVALIDATE((elm)->field.cqe_prev); \
535  _Q_INVALIDATE((elm)->field.cqe_next); \
536 } while (0)
537 
538 #define CIRCLEQ_REPLACE(head, elm, elm2, field) do { \
539  if (((elm2)->field.cqe_next = (elm)->field.cqe_next) == \
540  CIRCLEQ_END(head)) \
541  (head).cqh_last = (elm2); \
542  else \
543  (elm2)->field.cqe_next->field.cqe_prev = (elm2); \
544  if (((elm2)->field.cqe_prev = (elm)->field.cqe_prev) == \
545  CIRCLEQ_END(head)) \
546  (head).cqh_first = (elm2); \
547  else \
548  (elm2)->field.cqe_prev->field.cqe_next = (elm2); \
549  _Q_INVALIDATE((elm)->field.cqe_prev); \
550  _Q_INVALIDATE((elm)->field.cqe_next); \
551 } while (0)
552 
553 #define CIRCLEQ_FOREACH_SAFE(var, head, field, tvar) \
554  for ((var) = CIRCLEQ_FIRST(head); \
555  (var) != CIRCLEQ_END(head) && \
556  ((tvar) = CIRCLEQ_NEXT(var, field), 1); \
557  (var) = (tvar))
558 
559 #define CIRCLEQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar) \
560  for ((var) = CIRCLEQ_LAST(head, headname); \
561  (var) != CIRCLEQ_END(head) && \
562  ((tvar) = CIRCLEQ_PREV(var, headname, field), 1); \
563  (var) = (tvar))
564 
565 #endif /* !_SYS_QUEUE_H_ */