apr_ring.h

Apache V2.0.15 Alpha For Linuxhttpd-2_0_15-alpha.tar.Z

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/*
 * This code draws heavily from the 4.4BSD <sys/queue.h> macros
 * and Dean Gaudet's "splim/ring.h".
 * <http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/sys/queue.h>
 * <http://www.arctic.org/~dean/splim/>
 *
 * We'd use Dean's code directly if we could guarantee the
 * availability of inline functions.
 */

#ifndef APR_RING_H
#define APR_RING_H

/*
 * for offsetof()
 */
#include <stddef.h>

/**
 * @package Rings
 */
/*
 * A ring is a kind of doubly-linked list that can be manipulated
 * without knowing where its head is.
 */

/**
 * <p>The Ring Element</p>
 *
 * A ring element struct is linked to the other elements in the ring
 * through its ring entry field, e.g.
 * <pre>
 *      struct my_element_t {
 *          APR_RING_ENTRY(my_element_t) link;
 *          int foo;
 *          char *bar;
 *      };
 * </pre>
 * An element struct may be put on more than one ring if it has
 * more than one APR_RING_ENTRY field.
 *
 * @warning For strict C standards compliance you should put the APR_RING_ENTRY
 * first in the element struct unless the head is always part of a larger
 * object with enough earlier fields to accommodate the offsetof() used
 * to compute the ring sentinel below. You can usually ignore this caveat.
 * @defvar APR_RING_ENTRY
 */
#define APR_RING_ENTRY(elem)						\
    struct {								\
	struct elem *next;						\
	struct elem *prev;						\
    }

/**
 * <p>The Ring Head</p>
 *
 * Each ring is managed via its head, which is a struct declared like this:
 * <pre>
 *      APR_RING_HEAD(my_ring_t, my_element_t);
 *      struct my_ring_t ring, *ringp;
 * </pre>
 *
 * This struct looks just like the element link struct so that we can
 * be sure that the typecasting games will work as expected.
 *
 * The first element in the ring is next after the head, and the last
 * element is just before the head.
 * @defvar APR_RING_HEAD
 */
#define APR_RING_HEAD(head, elem)					\
    struct head {							\
	struct elem *next;						\
	struct elem *prev;						\
    }

/**
 * <p>The Ring Sentinel</p>
 *
 * This is the magic pointer value that occurs before the first and
 * after the last elements in the ring, computed from the address of
 * the ring's head.  The head itself isn't an element, but in order to
 * get rid of all the special cases when dealing with the ends of the
 * ring, we play typecasting games to make it look like one.
 *
 * @param hp   The head of the ring
 * @param elem The name of the element struct
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc elem *APR_RING_SENTINEL(head *hp, struct elem, APR_RING_ENTRY link)
 */
#define APR_RING_SENTINEL(hp, elem, link)				\
    (struct elem *)((char *)(hp) - offsetof(struct elem, link))

/**
 * The first element of the ring
 * @param hp   The head of the ring
 * @deffunc elem *APR_RING_FIRST(head *hp)
 */
#define APR_RING_FIRST(hp)	(hp)->next
/**
 * The last element of the ring
 * @param hp   The head of the ring
 * @deffunc elem *APR_RING_LAST(head *hp)
 */
#define APR_RING_LAST(hp)	(hp)->prev
/**
 * The next element in the ring
 * @param ep   The current element
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc elem *APR_RING_NEXT(elem *ep, APR_RING_ENTRY link)
 */
#define APR_RING_NEXT(ep, link)	(ep)->link.next
/**
 * The previous element in the ring
 * @param ep   The current element
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc elem *APR_RING_PREV(elem *ep, APR_RING_ENTRY link)
 */
#define APR_RING_PREV(ep, link)	(ep)->link.prev


/**
 * Initialize a ring
 * @param hp   The head of the ring
 * @param elem The name of the element struct
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc void APR_RING_INIT(head *hp, struct elem, APR_RING_ENTRY link)
 */
#define APR_RING_INIT(hp, elem, link) do {				\
	APR_RING_FIRST((hp)) = APR_RING_SENTINEL((hp), elem, link);	\
	APR_RING_LAST((hp))  = APR_RING_SENTINEL((hp), elem, link);	\
    } while (0)

/**
 * Determine if a ring is empty
 * @param hp   The head of the ring
 * @param elem The name of the element struct
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @return true or false
 * @deffunc int APR_RING_EMPTY(head *hp, struct elem, APR_RING_ENTRY link)
 */
#define APR_RING_EMPTY(hp, elem, link)					\
    (APR_RING_FIRST((hp)) == APR_RING_SENTINEL((hp), elem, link))

/**
 * Initialize a singleton element
 * @param ep   The element
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc void APR_RING_ELEM_INIT(elem *ep, APR_RING_ENTRY link)
 */
#define APR_RING_ELEM_INIT(ep, link) do {				\
	APR_RING_NEXT((ep), link) = (ep);				\
	APR_RING_PREV((ep), link) = (ep);				\
    } while (0)


/**
 * Splice the sequence ep1..epN into the ring before element lep
 *   (..lep.. becomes ..ep1..epN..lep..)
 * @warning This doesn't work for splicing before the first element or on
 *   empty rings... see APR_RING_SPLICE_HEAD for one that does
 * @param lep  Element in the ring to splice before
 * @param ep1  First element in the sequence to splice in
 * @param epN  Last element in the sequence to splice in
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc void APR_RING_SPLICE_BEFORE(elem *lep, elem *ep1, elem *epN, APR_RING_ENTRY link)
 */
#define APR_RING_SPLICE_BEFORE(lep, ep1, epN, link) do {		\
	APR_RING_NEXT((epN), link) = (lep);				\
	APR_RING_PREV((ep1), link) = APR_RING_PREV((lep), link);	\
	APR_RING_NEXT(APR_RING_PREV((lep), link), link) = (ep1);	\
	APR_RING_PREV((lep), link) = (epN);				\
    } while (0)

/**
 * Splice the sequence ep1..epN into the ring after element lep
 *   (..lep.. becomes ..lep..ep1..epN..)
 * @warning This doesn't work for splicing after the last element or on
 *   empty rings... see APR_RING_SPLICE_TAIL for one that does
 * @param lep  Element in the ring to splice after
 * @param ep1  First element in the sequence to splice in
 * @param epN  Last element in the sequence to splice in
 * @param link The name of the APR_RING_ENTRY in the element struct
 * @deffunc void APR_RING_SPLICE_AFTER(elem *lep, elem *ep1, elem *epN, APR_RING_ENTRY link)
 */
#define APR_RING_SPLICE_AFTER(lep, ep1, epN, link) do {			\
	APR_RING_PREV((ep1), link) = (lep);				\
	APR_RING_NEXT((epN), link) = APR_RING_NEXT((lep), link);	\