lmdb-erl/c_src/queue.h

/*
 * 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.
 * 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
 * $FreeBSD: src/sys/sys/queue.h,v 1.54 2002/08/05 05:18:43 alfred Exp $
 */

#ifndef	_DB_QUEUE_H_
#define	_DB_QUEUE_H_

#ifndef __offsetof
#define __offsetof(st, m) \
          ((size_t) ( (char *)&((st *)0)->m - (char *)0 ))
#endif

#ifndef __containerof
#define __containerof(ptr, type, member) ({ \
          const typeof( ((type *)0)->member ) *__mptr = (ptr);              \
                (type *)( (char *)__mptr - __offsetof(type,member) );})
#endif

#if defined(__cplusplus)
extern "C" {
#endif

/*
 * This file defines four types of data structures: singly-linked lists,
 * singly-linked tail queues, lists and tail 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 singly-linked 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
 * 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, at the head of the list, or at the
 * end of the list. Elements being removed from the head of the tail queue
 * should use the explicit macro for this purpose for optimum efficiency.
 * A singly-linked tail queue may only be traversed in the forward direction.
 * Singly-linked tail queues are ideal for applications with large datasets
 * and few or no removals or for implementing a FIFO 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 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.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 *
 *			SLIST	LIST	STAILQ	TAILQ
 * _HEAD		+	+	+	+
 * _HEAD_INITIALIZER	+	+	+	+
 * _ENTRY		+	+	+	+
 * _INIT		+	+	+	+
 * _EMPTY		+	+	+	+
 * _FIRST		+	+	+	+
 * _NEXT		+	+	+	+
 * _PREV		-	-	-	+
 * _LAST		-	-	+	+
 * _FOREACH		+	+	+	+
 * _FOREACH_REVERSE	-	-	-	+
 * _INSERT_HEAD		+	+	+	+
 * _INSERT_BEFORE	-	+	-	+
 * _INSERT_AFTER	+	+	+	+
 * _INSERT_TAIL		-	-	+	+
 * _CONCAT		-	-	+	+
 * _REMOVE_HEAD		+	-	+	-
 * _REMOVE		+	+	+	+
 *
 */

/*
 * XXX
 * We #undef all of the macros because there are incompatible versions of this
 * file and these macros on various systems.  What makes the problem worse is
 * they are included and/or defined by system include files which we may have
 * already loaded into Berkeley DB before getting here.  For example, FreeBSD's
 * <rpc/rpc.h> includes its system <sys/queue.h>, and VxWorks UnixLib.h defines
 * several of the LIST_XXX macros.  Visual C.NET 7.0 also defines some of these
 * same macros in Vc7\PlatformSDK\Include\WinNT.h.  Make sure we use ours.
 */
#undef LIST_EMPTY
#undef LIST_ENTRY
#undef LIST_FIRST
#undef LIST_FOREACH
#undef LIST_HEAD
#undef LIST_HEAD_INITIALIZER
#undef LIST_INIT
#undef LIST_INSERT_AFTER
#undef LIST_INSERT_BEFORE
#undef LIST_INSERT_HEAD
#undef LIST_NEXT
#undef LIST_REMOVE
#undef QMD_TRACE_ELEM
#undef QMD_TRACE_HEAD
#undef QUEUE_MACRO_DEBUG
#undef SLIST_EMPTY
#undef SLIST_ENTRY
#undef SLIST_FIRST
#undef SLIST_FOREACH
#undef SLIST_FOREACH_PREVPTR
#undef SLIST_HEAD
#undef SLIST_HEAD_INITIALIZER
#undef SLIST_INIT
#undef SLIST_INSERT_AFTER
#undef SLIST_INSERT_HEAD
#undef SLIST_NEXT
#undef SLIST_REMOVE
#undef SLIST_REMOVE_HEAD
#undef STAILQ_CONCAT
#undef STAILQ_EMPTY
#undef STAILQ_ENTRY
#undef STAILQ_FIRST
#undef STAILQ_FOREACH
#undef STAILQ_HEAD
#undef STAILQ_HEAD_INITIALIZER
#undef STAILQ_INIT
#undef STAILQ_INSERT_AFTER
#undef STAILQ_INSERT_HEAD
#undef STAILQ_INSERT_TAIL
#undef STAILQ_LAST
#undef STAILQ_NEXT
#undef STAILQ_REMOVE
#undef STAILQ_REMOVE_HEAD
#undef STAILQ_REMOVE_HEAD_UNTIL
#undef TAILQ_CONCAT
#undef TAILQ_EMPTY
#undef TAILQ_ENTRY
#undef TAILQ_FIRST
#undef TAILQ_FOREACH
#undef TAILQ_FOREACH_REVERSE
#undef TAILQ_HEAD
#undef TAILQ_HEAD_INITIALIZER
#undef TAILQ_INIT
#undef TAILQ_INSERT_AFTER
#undef TAILQ_INSERT_BEFORE
#undef TAILQ_INSERT_HEAD
#undef TAILQ_INSERT_TAIL
#undef TAILQ_LAST
#undef TAILQ_NEXT
#undef TAILQ_PREV
#undef TAILQ_REMOVE
#undef TRACEBUF
#undef TRASHIT

#define	QUEUE_MACRO_DEBUG 0
#if QUEUE_MACRO_DEBUG
/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
	char * lastfile;
	int lastline;
	char * prevfile;
	int prevline;
};

#define	TRACEBUF	struct qm_trace trace;
#define	TRASHIT(x)	do {(x) = (void *)-1;} while (0)

#define	QMD_TRACE_HEAD(head) do {					\
	(head)->trace.prevline = (head)->trace.lastline;		\
	(head)->trace.prevfile = (head)->trace.lastfile;		\
	(head)->trace.lastline = __LINE__;				\
	(head)->trace.lastfile = __FILE__;				\
} while (0)

#define	QMD_TRACE_ELEM(elem) do {					\
	(elem)->trace.prevline = (elem)->trace.lastline;		\
	(elem)->trace.prevfile = (elem)->trace.lastfile;		\
	(elem)->trace.lastline = __LINE__;				\
	(elem)->trace.lastfile = __FILE__;				\
} while (0)

#else
#define	QMD_TRACE_ELEM(elem)
#define	QMD_TRACE_HEAD(head)
#define	TRACEBUF
#define	TRASHIT(x)
#endif	/* QUEUE_MACRO_DEBUG */

/*
 * Singly-linked List declarations.
 */
#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_FOREACH(var, head, field)					\
	for ((var) = SLIST_FIRST((head));				\
	    (var);							\
	    (var) = SLIST_NEXT((var), field))

#define	SLIST_FOREACH_PREVPTR(var, varp, head, field)			\
	for ((varp) = &SLIST_FIRST((head));				\
	    ((var) = *(varp)) != NULL;					\
	    (varp) = &SLIST_NEXT((var), field))

#define	SLIST_INIT(head) do {						\
	SLIST_FIRST((head)) = NULL;					\
} while (0)

#define	SLIST_INSERT_AFTER(slistelm, elm, field) do {			\
	SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);	\
	SLIST_NEXT((slistelm), field) = (elm);				\
} while (0)

#define	SLIST_INSERT_HEAD(head, elm, field) do {			\
	SLIST_NEXT((elm), field) = SLIST_FIRST((head));			\
	SLIST_FIRST((head)) = (elm);					\
} while (0)

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

#define	SLIST_REMOVE(head, elm, type, field) do {			\
	if (SLIST_FIRST((head)) == (elm)) {				\
		SLIST_REMOVE_HEAD((head), field);			\
	}								\
	else {								\
		struct type *curelm = SLIST_FIRST((head));		\
		while (SLIST_NEXT(curelm, field) != (elm))		\
			curelm = SLIST_NEXT(curelm, field);		\
		SLIST_NEXT(curelm, field) =				\
		    SLIST_NEXT(SLIST_NEXT(curelm, field), field);	\
	}								\
} while (0)

#define	SLIST_REMOVE_HEAD(head, field) do {				\
	SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);	\
} while (0)

/*
 * Singly-linked Tail queue declarations.
 */
#define	STAILQ_HEAD(name, type)						\
struct name {								\
	struct type *stqh_first;/* first element */			\
	struct type **stqh_last;/* addr of last next element */		\
}

#define	STAILQ_HEAD_INITIALIZER(head)					\
	{ NULL, &(head).stqh_first }

#define	STAILQ_ENTRY(type)						\
struct {								\
	struct type *stqe_next;	/* next element */			\
}

/*
 * Singly-linked Tail queue functions.
 */
#define	STAILQ_CONCAT(head1, head2) do {				\
	if (!STAILQ_EMPTY((head2))) {					\
		*(head1)->stqh_last = (head2)->stqh_first;		\
		(head1)->stqh_last = (head2)->stqh_last;		\
		STAILQ_INIT((head2));					\
	}								\
} while (0)

#define	STAILQ_EMPTY(head)	((head)->stqh_first == NULL)

#define	STAILQ_FIRST(head)	((head)->stqh_first)

#define	STAILQ_FOREACH(var, head, field)				\
	for ((var) = STAILQ_FIRST((head));				\
	   (var);							\
	   (var) = STAILQ_NEXT((var), field))

#define	STAILQ_INIT(head) do {						\
	STAILQ_FIRST((head)) = NULL;					\
	(head)->stqh_last = &STAILQ_FIRST((head));			\
} while (0)

#define	STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {		\
	if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
	STAILQ_NEXT((tqelm), field) = (elm);				\
} while (0)

#define	STAILQ_INSERT_HEAD(head, elm, field) do {			\
	if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL)	\
		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
	STAILQ_FIRST((head)) = (elm);					\
} while (0)

#define	STAILQ_INSERT_TAIL(head, elm, field) do {			\
	STAILQ_NEXT((elm), field) = NULL;				\
	*(head)->stqh_last = (elm);					\
	(head)->stqh_last = &STAILQ_NEXT((elm), field);			\
} while (0)

#define	STAILQ_LAST(head, type, field)					\
	(STAILQ_EMPTY((head)) ?						\
		NULL :							\
		((struct type *)					\
		((char *)((head)->stqh_last) - __offsetof(struct type, field))))

#define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)

#define	STAILQ_REMOVE(head, elm, type, field) do {			\
	if (STAILQ_FIRST((head)) == (elm)) {				\
		STAILQ_REMOVE_HEAD((head), field);			\
	}								\
	else {								\
		struct type *curelm = STAILQ_FIRST((head));		\
		while (STAILQ_NEXT(curelm, field) != (elm))		\
			curelm = STAILQ_NEXT(curelm, field);		\
		if ((STAILQ_NEXT(curelm, field) =			\
		     STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
			(head)->stqh_last = &STAILQ_NEXT((curelm), field);\
	}								\
} while (0)

#define	STAILQ_REMOVE_HEAD(head, field) do {				\
	if ((STAILQ_FIRST((head)) =					\
	     STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)		\
		(head)->stqh_last = &STAILQ_FIRST((head));		\
} while (0)

#define	STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {			\
	if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL)	\
		(head)->stqh_last = &STAILQ_FIRST((head));		\
} while (0)

/*
 * List declarations.
 */
#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.
 */

#define	LIST_EMPTY(head)	((head)->lh_first == NULL)

#define	LIST_FIRST(head)	((head)->lh_first)

#define	LIST_FOREACH(var, head, field)					\
	for ((var) = LIST_FIRST((head));				\
	    (var);							\
	    (var) = LIST_NEXT((var), field))

#define	LIST_INIT(head) do {						\
	LIST_FIRST((head)) = NULL;					\
} while (0)

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

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

#define	LIST_INSERT_HEAD(head, elm, field) do {				\
	if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)	\
		LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
	LIST_FIRST((head)) = (elm);					\
	(elm)->field.le_prev = &LIST_FIRST((head));			\
} while (0)

#define	LIST_NEXT(elm, field)	((elm)->field.le_next)

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

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

#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 */	\
	TRACEBUF							\
}

/*
 * Tail queue functions.
 */
#define	TAILQ_CONCAT(head1, head2, field) do {				\
	if (!TAILQ_EMPTY(head2)) {					\
		*(head1)->tqh_last = (head2)->tqh_first;		\
		(head2)->tqh_first->field.tqe_prev = (head1)->tqh_last;	\
		(head1)->tqh_last = (head2)->tqh_last;			\
		TAILQ_INIT((head2));					\
		QMD_TRACE_HEAD(head);					\
		QMD_TRACE_HEAD(head2);					\
	}								\
} while (0)

#define	TAILQ_EMPTY(head)	((head)->tqh_first == NULL)

#define	TAILQ_FIRST(head)	((head)->tqh_first)

#define	TAILQ_FOREACH(var, head, field)					\
	for ((var) = TAILQ_FIRST((head));				\
	    (var);							\
	    (var) = TAILQ_NEXT((var), field))

#define	TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
	for ((var) = TAILQ_LAST((head), headname);			\
	    (var);							\
	    (var) = TAILQ_PREV((var), headname, field))

#define	TAILQ_INIT(head) do {						\
	TAILQ_FIRST((head)) = NULL;					\
	(head)->tqh_last = &TAILQ_FIRST((head));			\
	QMD_TRACE_HEAD(head);						\
} while (0)

#define	TAILQ_INSERT_AFTER(head, listelm, elm, field) do {		\
	if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
		TAILQ_NEXT((elm), field)->field.tqe_prev =		\
		    &TAILQ_NEXT((elm), field);				\
	else {								\
		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
		QMD_TRACE_HEAD(head);					\
	}								\
	TAILQ_NEXT((listelm), field) = (elm);				\
	(elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);		\
	QMD_TRACE_ELEM(&(elm)->field);					\
	QMD_TRACE_ELEM(&listelm->field);				\
} while (0)

#define	TAILQ_INSERT_BEFORE(listelm, elm, field) do {			\
	(elm)->field.tqe_prev = (listelm)->field.tqe_prev;		\
	TAILQ_NEXT((elm), field) = (listelm);				\
	*(listelm)->field.tqe_prev = (elm);				\
	(listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);		\
	QMD_TRACE_ELEM(&(elm)->field);					\
	QMD_TRACE_ELEM(&listelm->field);				\
} while (0)

#define	TAILQ_INSERT_HEAD(head, elm, field) do {			\
	if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)	\
		TAILQ_FIRST((head))->field.tqe_prev =			\
		    &TAILQ_NEXT((elm), field);				\
	else								\
		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
	TAILQ_FIRST((head)) = (elm);					\
	(elm)->field.tqe_prev = &TAILQ_FIRST((head));			\
	QMD_TRACE_HEAD(head);						\
	QMD_TRACE_ELEM(&(elm)->field);					\
} while (0)

#define	TAILQ_INSERT_TAIL(head, elm, field) do {			\
	TAILQ_NEXT((elm), field) = NULL;				\
	(elm)->field.tqe_prev = (head)->tqh_last;			\
	*(head)->tqh_last = (elm);					\
	(head)->tqh_last = &TAILQ_NEXT((elm), field);			\
	QMD_TRACE_HEAD(head);						\
	QMD_TRACE_ELEM(&(elm)->field);					\
} while (0)

#define	TAILQ_LAST(head, headname)					\
	(*(((struct headname *)((head)->tqh_last))->tqh_last))

#define	TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

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

#define	TAILQ_REMOVE(head, elm, field) do {				\
	if ((TAILQ_NEXT((elm), field)) != NULL)				\
		TAILQ_NEXT((elm), field)->field.tqe_prev =		\
		    (elm)->field.tqe_prev;				\
	else {								\
		(head)->tqh_last = (elm)->field.tqe_prev;		\
		QMD_TRACE_HEAD(head);					\
	}								\
	*(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);		\
	TRASHIT((elm)->field.tqe_next);					\
	TRASHIT((elm)->field.tqe_prev);					\
	QMD_TRACE_ELEM(&(elm)->field);					\
} while (0)

/*
 * 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) != (const void *)(head);				\
		(var) = ((var)->field.cqe_next))

#define	CIRCLEQ_FOREACH_REVERSE(var, head, field)			\
	for ((var) = ((head)->cqh_last);				\
		(var) != (const 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)

#define CIRCLEQ_LOOP_NEXT(head, elm, field)				\
	(((elm)->field.cqe_next == (void *)(head))			\
	    ? ((head)->cqh_first)					\
	    : (elm->field.cqe_next))
#define CIRCLEQ_LOOP_PREV(head, elm, field)				\
	(((elm)->field.cqe_prev == (void *)(head))			\
	    ? ((head)->cqh_last)					\
	    : (elm->field.cqe_prev))


#if defined(__cplusplus)
}
#endif
#endif	/* !_DB_QUEUE_H_ */