queue.h

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/*
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)queue.h     8.5 (Berkeley) 8/20/94
 */

#ifndef _SYS_QUEUE_H_
#define _SYS_QUEUE_H_

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues, and circular queues.
 *
 * A singly-linked list is headed by a single forward pointer. The
 * elements are singly linked for minimum space and pointer manipulation
 * overhead at the expense of O(n) removal for arbitrary elements. New
 * elements can be added to the list after an existing element or at the
 * head of the list.  Elements being removed from the head of the list
 * should use the explicit macro for this purpose for optimum
 * efficiency. A singly-linked list may only be traversed in the forward
 * direction.  Singly-linked lists are ideal for applications with large
 * datasets and few or no removals or for implementing a LIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A simple queue is headed by a pair of pointers, one the head of the
 * list and the other to the tail of the list. The elements are singly
 * linked to save space, so only elements can only be removed from the
 * head of the list. New elements can be added to the list after
 * an existing element, at the head of the list, or at the end of the
 * list. A simple queue may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * A circle queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or after
 * an existing element, at the head of the list, or at the end of the list.
 * A circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 */

/*
 * List definitions.
 */
#define LIST_HEAD(name, type)                                           \
struct name {                                                           \
        struct type *lh_first;  /* first element */                     \
}

#define LIST_HEAD_INITIALIZER(head)                                     \
        { NULL }

#define LIST_ENTRY(type)                                                \
struct {                                                                \
        struct type *le_next;   /* next element */                      \
        struct type **le_prev;  /* address of previous next element */  \
}

/*
 * List functions.
 */
#if defined(QUEUEDEBUG)
#define QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)                   \
        if ((head)->lh_first &&                                         \
            (head)->lh_first->field.le_prev != &(head)->lh_first)       \
                panic("LIST_INSERT_HEAD %p %s:%d", (head), __FILE__, __LINE__);
#define QUEUEDEBUG_LIST_OP(elm, field)                                  \
        if ((elm)->field.le_next &&                                     \
            (elm)->field.le_next->field.le_prev !=                      \
            &(elm)->field.le_next)                                      \
                panic("LIST_* forw %p %s:%d", (elm), __FILE__, __LINE__);\
        if (*(elm)->field.le_prev != (elm))                             \
                panic("LIST_* back %p %s:%d", (elm), __FILE__, __LINE__);
#define QUEUEDEBUG_LIST_POSTREMOVE(elm, field)                          \
        (elm)->field.le_next = (void *)1L;                              \
        (elm)->field.le_prev = (void *)1L;
#else
#define QUEUEDEBUG_LIST_INSERT_HEAD(head, elm, field)
#define QUEUEDEBUG_LIST_OP(elm, field)
#define QUEUEDEBUG_LIST_POSTREMOVE(elm, field)
#endif

#define LIST_INIT(head) do {                                            \
        (head)->lh_first = NULL;                                        \
} while (/*CONSTCOND*/0)

#define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
        QUEUEDEBUG_LIST_OP((listelm), field)                            \
        if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
                (listelm)->field.le_next->field.le_prev =               \
                    &(elm)->field.le_next;                              \
        (listelm)->field.le_next = (elm);                               \
        (elm)->field.le_prev = &(listelm)->field.le_next;               \
} while (/*CONSTCOND*/0)

#define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
        QUEUEDEBUG_LIST_OP((listelm), field)                            \
        (elm)->field.le_prev = (listelm)->field.le_prev;                \
        (elm)->field.le_next = (listelm);                               \
        *(listelm)->field.le_prev = (elm);                              \
        (listelm)->field.le_prev = &(elm)->field.le_next;               \
} while (/*CONSTCOND*/0)

#define LIST_INSERT_HEAD(head, elm, field) do {                         \
        QUEUEDEBUG_LIST_INSERT_HEAD((head), (elm), field)               \
        if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
                (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
        (head)->lh_first = (elm);                                       \
        (elm)->field.le_prev = &(head)->lh_first;                       \
} while (/*CONSTCOND*/0)

#define LIST_REMOVE(elm, field) do {                                    \
        QUEUEDEBUG_LIST_OP((elm), field)                                \
        if ((elm)->field.le_next != NULL)                               \
                (elm)->field.le_next->field.le_prev =                   \
                    (elm)->field.le_prev;                               \
        *(elm)->field.le_prev = (elm)->field.le_next;                   \
        QUEUEDEBUG_LIST_POSTREMOVE((elm), field)                        \
} while (/*CONSTCOND*/0)

#define LIST_FOREACH(var, head, field)                                  \
        for ((var) = ((head)->lh_first);                                \
                (var);                                                  \
                (var) = ((var)->field.le_next))

/*
 * List access methods.
 */
#define LIST_EMPTY(head)                ((head)->lh_first == NULL)
#define LIST_FIRST(head)                ((head)->lh_first)
#define LIST_NEXT(elm, field)           ((elm)->field.le_next)

/*
 * Singly-linked List definitions.
 */
#define SLIST_HEAD(name, type)                                          \
struct name {                                                           \
        struct type *slh_first; /* first element */                     \
}

#define SLIST_HEAD_INITIALIZER(head)                                    \
        { NULL }
 
#define SLIST_ENTRY(type)                                               \
struct {                                                                \
        struct type *sle_next;  /* next element */                      \
}
 
/*
 * Singly-linked List functions.
 */
#define SLIST_EMPTY(head)       ((head)->slh_first == NULL)
#define SLIST_FIRST(head)       ((head)->slh_first)
#define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)

#define SLIST_FOREACH(var, head, field)                                 \
        for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)

#define SLIST_INIT(head) do {                                           \
        (head)->slh_first = NULL;                                       \
} while (/*CONSTCOND*/0)

#define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
        (elm)->field.sle_next = (slistelm)->field.sle_next;             \
        (slistelm)->field.sle_next = (elm);                             \
} while (/*CONSTCOND*/0)

#define SLIST_INSERT_HEAD(head, elm, field) do {                        \
        (elm)->field.sle_next = (head)->slh_first;                      \
        (head)->slh_first = (elm);                                      \
} while (/*CONSTCOND*/0)

#define SLIST_NEXT(elm, field)  ((elm)->field.sle_next)

#define SLIST_REMOVE_HEAD(head, field) do {                             \
        (head)->slh_first = (head)->slh_first->field.sle_next;          \
} while (/*CONSTCOND*/0)

#define SLIST_REMOVE(head, elm, type, field) do {                       \
        if ((head)->slh_first == (elm)) {                               \
                SLIST_REMOVE_HEAD((head), field);                       \
        }                                                               \
        else {                                                          \
                struct type *curelm = (head)->slh_first;                \
                while(curelm->field.sle_next != (elm))                  \
                        curelm = curelm->field.sle_next;                \
                curelm->field.sle_next =                                \
                    curelm->field.sle_next->field.sle_next;             \
        }                                                               \
} while (/*CONSTCOND*/0)

/*
 * Simple queue definitions.
 */
#define SIMPLEQ_HEAD(name, type)                                        \
struct name {                                                           \
        struct type *sqh_first; /* first element */                     \
        struct type **sqh_last; /* addr of last next element */         \
}

#define SIMPLEQ_HEAD_INITIALIZER(head)                                  \
        { NULL, &(head).sqh_first }

#define SIMPLEQ_ENTRY(type)                                             \
struct {                                                                \
        struct type *sqe_next;  /* next element */                      \
}

/*
 * Simple queue functions.
 */
#define SIMPLEQ_INIT(head) do {                                         \
        (head)->sqh_first = NULL;                                       \
        (head)->sqh_last = &(head)->sqh_first;                          \
} while (/*CONSTCOND*/0)

#define SIMPLEQ_INSERT_HEAD(head, elm, field) do {                      \
        if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)        \
                (head)->sqh_last = &(elm)->field.sqe_next;              \
        (head)->sqh_first = (elm);                                      \
} while (/*CONSTCOND*/0)

#define SIMPLEQ_INSERT_TAIL(head, elm, field) do {                      \
        (elm)->field.sqe_next = NULL;                                   \
        *(head)->sqh_last = (elm);                                      \
        (head)->sqh_last = &(elm)->field.sqe_next;                      \
} while (/*CONSTCOND*/0)

#define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
        if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
                (head)->sqh_last = &(elm)->field.sqe_next;              \
        (listelm)->field.sqe_next = (elm);                              \
} while (/*CONSTCOND*/0)

#define SIMPLEQ_REMOVE_HEAD(head, elm, field) do {                      \
        if (((head)->sqh_first = (elm)->field.sqe_next) == NULL)        \
                (head)->sqh_last = &(head)->sqh_first;                  \
} while (/*CONSTCOND*/0)

#define SIMPLEQ_FOREACH(var, head, field)                               \
        for ((var) = ((head)->sqh_first);                               \
                (var);                                                  \
                (var) = ((var)->field.sqe_next))

/*
 * Simple queue access methods.
 */
#define SIMPLEQ_EMPTY(head)             ((head)->sqh_first == NULL)
#define SIMPLEQ_FIRST(head)             ((head)->sqh_first)
#define SIMPLEQ_NEXT(elm, field)        ((elm)->field.sqe_next)

/*
 * Tail queue definitions.
 */
#define TAILQ_HEAD(name, type)                                          \
struct name {                                                           \
        struct type *tqh_first; /* first element */                     \
        struct type **tqh_last; /* addr of last next element */         \
}

#define TAILQ_HEAD_INITIALIZER(head)                                    \
        { NULL, &(head).tqh_first }

#define TAILQ_ENTRY(type)                                               \
struct {                                                                \
        struct type *tqe_next;  /* next element */                      \
        struct type **tqe_prev; /* address of previous next element */  \
}

/*
 * Tail queue functions.
 */
#if defined(QUEUEDEBUG)
#define QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)                  \
        if ((head)->tqh_first &&                                        \
            (head)->tqh_first->field.tqe_prev != &(head)->tqh_first)    \
                panic("TAILQ_INSERT_HEAD %p %s:%d", (head), __FILE__, __LINE__);
#define QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)                  \
        if (*(head)->tqh_last != NULL)                                  \
                panic("TAILQ_INSERT_TAIL %p %s:%d", (head), __FILE__, __LINE__);
#define QUEUEDEBUG_TAILQ_OP(elm, field)                                 \
        if ((elm)->field.tqe_next &&                                    \
            (elm)->field.tqe_next->field.tqe_prev !=                    \
            &(elm)->field.tqe_next)                                     \
                panic("TAILQ_* forw %p %s:%d", (elm), __FILE__, __LINE__);\
        if (*(elm)->field.tqe_prev != (elm))                            \
                panic("TAILQ_* back %p %s:%d", (elm), __FILE__, __LINE__);
#define QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)                         \
        (elm)->field.tqe_next = (void *)1L;                             \
        (elm)->field.tqe_prev = (void *)1L;
#else
#define QUEUEDEBUG_TAILQ_INSERT_HEAD(head, elm, field)
#define QUEUEDEBUG_TAILQ_INSERT_TAIL(head, elm, field)
#define QUEUEDEBUG_TAILQ_OP(elm, field)
#define QUEUEDEBUG_TAILQ_POSTREMOVE(elm, field)
#endif

#define TAILQ_INIT(head) do {                                           \
        (head)->tqh_first = NULL;                                       \
        (head)->tqh_last = &(head)->tqh_first;                          \
} while (/*CONSTCOND*/0)

#define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
        QUEUEDEBUG_TAILQ_INSERT_HEAD((head), (elm), field)              \
        if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
                (head)->tqh_first->field.tqe_prev =                     \
                    &(elm)->field.tqe_next;                             \
        else                                                            \
                (head)->tqh_last = &(elm)->field.tqe_next;              \
                (head)->tqh_first = (elm);                              \
        (elm)->field.tqe_prev = &(head)->tqh_first;                     \
} while (/*CONSTCOND*/0)

#define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
        QUEUEDEBUG_TAILQ_INSERT_TAIL((head), (elm), field)              \
        (elm)->field.tqe_next = NULL;                                   \
        (elm)->field.tqe_prev = (head)->tqh_last;                       \
        *(head)->tqh_last = (elm);                                      \
        (head)->tqh_last = &(elm)->field.tqe_next;                      \
} while (/*CONSTCOND*/0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
        QUEUEDEBUG_TAILQ_OP((listelm), field)                           \
        if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
                (elm)->field.tqe_next->field.tqe_prev =                 \
                    &(elm)->field.tqe_next;                             \
        else                                                            \
                (head)->tqh_last = &(elm)->field.tqe_next;              \
        (listelm)->field.tqe_next = (elm);                              \
        (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
} while (/*CONSTCOND*/0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
        QUEUEDEBUG_TAILQ_OP((listelm), field)                           \
        (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
        (elm)->field.tqe_next = (listelm);                              \
        *(listelm)->field.tqe_prev = (elm);                             \
        (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
} while (/*CONSTCOND*/0)

#define TAILQ_REMOVE(head, elm, field) do {                             \
        QUEUEDEBUG_TAILQ_OP((elm), field)                               \
        if (((elm)->field.tqe_next) != NULL)                            \
                (elm)->field.tqe_next->field.tqe_prev =                 \
                    (elm)->field.tqe_prev;                              \
        else                                                            \
                (head)->tqh_last = (elm)->field.tqe_prev;               \
        *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
        QUEUEDEBUG_TAILQ_POSTREMOVE((elm), field);                      \
} while (/*CONSTCOND*/0)

/*
 * Tail queue access methods.
 */
#define TAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
#define TAILQ_FIRST(head)               ((head)->tqh_first)
#define TAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)

#define TAILQ_LAST(head, headname) \
        (*(((struct headname *)((head)->tqh_last))->tqh_last))
#define TAILQ_PREV(elm, headname, field) \
        (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))

#define TAILQ_FOREACH(var, head, field)                                 \
        for ((var) = ((head)->tqh_first);                               \
                (var);                                                  \
                (var) = ((var)->field.tqe_next))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
        for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
                (var);                                                  \
                (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))

/*
 * Circular queue definitions.
 */
#define CIRCLEQ_HEAD(name, type)                                        \
struct name {                                                           \
        struct type *cqh_first;         /* first element */             \
        struct type *cqh_last;          /* last element */              \
}

#define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
        { (void *)&head, (void *)&head }

#define CIRCLEQ_ENTRY(type)                                             \
struct {                                                                \
        struct type *cqe_next;          /* next element */              \
        struct type *cqe_prev;          /* previous element */          \
}

/*
 * Circular queue functions.
 */
#define CIRCLEQ_INIT(head) do {                                         \
        (head)->cqh_first = (void *)(head);                             \
        (head)->cqh_last = (void *)(head);                              \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
        (elm)->field.cqe_next = (listelm)->field.cqe_next;              \
        (elm)->field.cqe_prev = (listelm);                              \
        if ((listelm)->field.cqe_next == (void *)(head))                \
                (head)->cqh_last = (elm);                               \
        else                                                            \
                (listelm)->field.cqe_next->field.cqe_prev = (elm);      \
        (listelm)->field.cqe_next = (elm);                              \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
        (elm)->field.cqe_next = (listelm);                              \
        (elm)->field.cqe_prev = (listelm)->field.cqe_prev;              \
        if ((listelm)->field.cqe_prev == (void *)(head))                \
                (head)->cqh_first = (elm);                              \
        else                                                            \
                (listelm)->field.cqe_prev->field.cqe_next = (elm);      \
        (listelm)->field.cqe_prev = (elm);                              \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
        (elm)->field.cqe_next = (head)->cqh_first;                      \
        (elm)->field.cqe_prev = (void *)(head);                         \
        if ((head)->cqh_last == (void *)(head))                         \
                (head)->cqh_last = (elm);                               \
        else                                                            \
                (head)->cqh_first->field.cqe_prev = (elm);              \
        (head)->cqh_first = (elm);                                      \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
        (elm)->field.cqe_next = (void *)(head);                         \
        (elm)->field.cqe_prev = (head)->cqh_last;                       \
        if ((head)->cqh_first == (void *)(head))                        \
                (head)->cqh_first = (elm);                              \
        else                                                            \
                (head)->cqh_last->field.cqe_next = (elm);               \
        (head)->cqh_last = (elm);                                       \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_REMOVE(head, elm, field) do {                           \
        if ((elm)->field.cqe_next == (void *)(head))                    \
                (head)->cqh_last = (elm)->field.cqe_prev;               \
        else                                                            \
                (elm)->field.cqe_next->field.cqe_prev =                 \
                    (elm)->field.cqe_prev;                              \
        if ((elm)->field.cqe_prev == (void *)(head))                    \
                (head)->cqh_first = (elm)->field.cqe_next;              \
        else                                                            \
                (elm)->field.cqe_prev->field.cqe_next =                 \
                    (elm)->field.cqe_next;                              \
} while (/*CONSTCOND*/0)

#define CIRCLEQ_FOREACH(var, head, field)                               \
        for ((var) = ((head)->cqh_first);                               \
                (var) != (void *)(head);                                \
                (var) = ((var)->field.cqe_next))

#define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
        for ((var) = ((head)->cqh_last);                                \
                (var) != (void *)(head);                                \
                (var) = ((var)->field.cqe_prev))

/*
 * Circular queue access methods.
 */
#define CIRCLEQ_EMPTY(head)             ((head)->cqh_first == (void *)(head))
#define CIRCLEQ_FIRST(head)             ((head)->cqh_first)
#define CIRCLEQ_LAST(head)              ((head)->cqh_last)
#define CIRCLEQ_NEXT(elm, field)        ((elm)->field.cqe_next)
#define CIRCLEQ_PREV(elm, field)        ((elm)->field.cqe_prev)


/*
 * LSE/OS Run queue definitions.
 * Copyright (c)2004 Arhur Kopatsy
 */
#define RUNQ_HEAD(name, type)                                           \
struct name {                                                           \
        struct type *rqh_ptr;           /* ptr element */               \
        int          flg;                                               \
}

#define RUNQ_HEAD_INITIALIZER(head)                                     \
        { NULL }

#define RUNQ_ENTRY(type)                                                \
struct {                                                                \
        struct type *rqe_next;          /* next element */              \
        struct type *rqe_prev;          /* previous element */          \
}

/*
 * Run queue functions.
 */
#define RUNQ_INIT(head) do {                                            \
        (head)->rqh_ptr = NULL;                                         \
} while (/*CONSTCOND*/0)

#define RUNQ_INSERT_BEFORE(head, listelm, elm, field) do {              \
        (elm)->field.rqe_next = (listelm);                              \
        (elm)->field.rqe_prev = (listelm)->field.rqe_prev;              \
        (listelm)->field.rqe_prev->field.rqe_next = (elm);              \
        (listelm)->field.rqe_prev = (elm);                              \
} while (/*CONSTCOND*/0)

#define RUNQ_SET_PTR(head, elm, field) do {                             \
        (head)->rqh_ptr = (elm);                                        \
        (elm)->field.rqe_next = (elm);                                  \
        (elm)->field.rqe_prev = (elm);                                  \
} while (/*CONSTCOND*/0)

#define RUNQ_REMOVE(head, elm, field) do {                              \
        if ((elm)->field.rqe_next == (elm))                             \
                (head)->rqh_ptr = NULL;                                 \
        else                                                            \
        {                                                               \
                (elm)->field.rqe_next->field.rqe_prev =                 \
                    (elm)->field.rqe_prev;                              \
                (elm)->field.rqe_prev->field.rqe_next =                 \
                    (elm)->field.rqe_next;                              \
        }                                                               \
} while (/*CONSTCOND*/0)

#define RUNQ_FOREACH(var, head, field)                                  \
        for ((head)->flg = 0, (var) = ((head)->rqh_ptr);                \
                ((head)->flg == 0 || (var) != (head)->rqh_ptr) &&       \
                                                (var) != NULL;          \
                (var) = ((var)->field.rqe_next), (head)->flg = 1)

/*
 * Circular queue access methods.
 */
#define RUNQ_EMPTY(head)        ((head)->rqh_ptr == NULL)
#define RUNQ_NEXT(elm, field)   ((elm)->field.rqe_next)
#define RUNQ_PREV(elm, field)   ((elm)->field.rqe_prev)

#endif  /* !_SYS_QUEUE_H_ */

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