*
*
* We'd use Dean's code directly if we could guarantee the
* availability of inline functions.
*/
/**
* @file apr_ring.h
* @brief APR-Util Rings
*/
#ifndef APR_RING_H
#define APR_RING_H
/*
* for offsetof()
*/
#include "apr_general.h"
/**
* @defgroup APR_Util_Rings Rings
* @ingroup APR_Util
* @{
*/
/**
* A ring is a kind of doubly-linked list that can be manipulated
* without knowing where its head is.
*/
/**
* The Ring Element
*
* A ring element struct is linked to the other elements in the ring
* through its ring entry field, e.g.
*
* struct my_element_t {
* APR_RING_ENTRY(my_element_t) link;
* int foo;
* char *bar;
* };
*
* 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.
*/
#define APR_RING_ENTRY(elem) \
struct { \
struct elem *next; \
struct elem *prev; \
}
/**
* The Ring Head
*
* Each ring is managed via its head, which is a struct declared like this:
*
* APR_RING_HEAD(my_ring_t, my_element_t);
* struct my_ring_t ring, *ringp;
*
*
* 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.
*/
#define APR_RING_HEAD(head, elem) \
struct head { \
struct elem *next; \
struct elem *prev; \
}
/**
* The Ring Sentinel
*
* 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
*/
#define APR_RING_SENTINEL(hp, elem, link) \
(struct elem *)((char *)(hp) - APR_XtOffsetOf(struct elem, link))
/**
* The first element of the ring
* @param hp The head of the ring
*/
#define APR_RING_FIRST(hp) (hp)->next
/**
* The last element of the ring
* @param hp The head of the ring
*/
#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
*/
#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
*/
#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
*/
#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
*/
#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
*/
#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
*/
#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
*/
#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); \
APR_RING_PREV(APR_RING_NEXT((lep), link), link) = (epN); \
APR_RING_NEXT((lep), link) = (ep1); \
} while (0)
/**
* Insert the element nep into the ring before element lep
* (..lep.. becomes ..nep..lep..)
* @warning This doesn't work for inserting before the first element or on
* empty rings... see APR_RING_INSERT_HEAD for one that does
* @param lep Element in the ring to insert before
* @param nep Element to insert
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_INSERT_BEFORE(lep, nep, link) \
APR_RING_SPLICE_BEFORE((lep), (nep), (nep), link)
/**
* Insert the element nep into the ring after element lep
* (..lep.. becomes ..lep..nep..)
* @warning This doesn't work for inserting after the last element or on
* empty rings... see APR_RING_INSERT_TAIL for one that does
* @param lep Element in the ring to insert after
* @param nep Element to insert
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_INSERT_AFTER(lep, nep, link) \
APR_RING_SPLICE_AFTER((lep), (nep), (nep), link)
/**
* Splice the sequence ep1..epN into the ring before the first element
* (..hp.. becomes ..hp..ep1..epN..)
* @param hp Head of the ring
* @param ep1 First element in the sequence to splice in
* @param epN Last element in the sequence to splice in
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_SPLICE_HEAD(hp, ep1, epN, elem, link) \
APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((hp), elem, link), \
(ep1), (epN), link)
/**
* Splice the sequence ep1..epN into the ring after the last element
* (..hp.. becomes ..ep1..epN..hp..)
* @param hp Head of the ring
* @param ep1 First element in the sequence to splice in
* @param epN Last element in the sequence to splice in
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_SPLICE_TAIL(hp, ep1, epN, elem, link) \
APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((hp), elem, link), \
(ep1), (epN), link)
/**
* Insert the element nep into the ring before the first element
* (..hp.. becomes ..hp..nep..)
* @param hp Head of the ring
* @param nep Element to insert
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_INSERT_HEAD(hp, nep, elem, link) \
APR_RING_SPLICE_HEAD((hp), (nep), (nep), elem, link)
/**
* Insert the element nep into the ring after the last element
* (..hp.. becomes ..nep..hp..)
* @param hp Head of the ring
* @param nep Element to insert
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_INSERT_TAIL(hp, nep, elem, link) \
APR_RING_SPLICE_TAIL((hp), (nep), (nep), elem, link)
/**
* Concatenate ring h2 onto the end of ring h1, leaving h2 empty.
* @param h1 Head of the ring to concatenate onto
* @param h2 Head of the ring to concatenate
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_CONCAT(h1, h2, elem, link) do { \
if (!APR_RING_EMPTY((h2), elem, link)) { \
APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((h1), elem, link), \
APR_RING_FIRST((h2)), \
APR_RING_LAST((h2)), link); \
APR_RING_INIT((h2), elem, link); \
} \
} while (0)
/**
* Prepend ring h2 onto the beginning of ring h1, leaving h2 empty.
* @param h1 Head of the ring to prepend onto
* @param h2 Head of the ring to prepend
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_PREPEND(h1, h2, elem, link) do { \
if (!APR_RING_EMPTY((h2), elem, link)) { \
APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((h1), elem, link), \
APR_RING_FIRST((h2)), \
APR_RING_LAST((h2)), link); \
APR_RING_INIT((h2), elem, link); \
} \
} while (0)
/**
* Unsplice a sequence of elements from a ring
* @warning The unspliced sequence is left with dangling pointers at either end
* @param ep1 First element in the sequence to unsplice
* @param epN Last element in the sequence to unsplice
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_UNSPLICE(ep1, epN, link) do { \
APR_RING_NEXT(APR_RING_PREV((ep1), link), link) = \
APR_RING_NEXT((epN), link); \
APR_RING_PREV(APR_RING_NEXT((epN), link), link) = \
APR_RING_PREV((ep1), link); \
} while (0)
/**
* Remove a single element from a ring
* @warning The unspliced element is left with dangling pointers at either end
* @param ep Element to remove
* @param link The name of the APR_RING_ENTRY in the element struct
*/
#define APR_RING_REMOVE(ep, link) \
APR_RING_UNSPLICE((ep), (ep), link)
/**
* Iterate through a ring
* @param ep The current element
* @param hp The ring to iterate over
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
* @remark This is the same as either:
*
* ep = APR_RING_FIRST(hp);
* while (ep != APR_RING_SENTINEL(hp, elem, link)) {
* ...
* ep = APR_RING_NEXT(ep, link);
* }
* OR
* for (ep = APR_RING_FIRST(hp);
* ep != APR_RING_SENTINEL(hp, elem, link);
* ep = APR_RING_NEXT(ep, link)) {
* ...
* }
*
* @warning Be aware that you cannot change the value of ep within
* the foreach loop, nor can you destroy the ring element it points to.
* Modifying the prev and next pointers of the element is dangerous
* but can be done if you're careful. If you change ep's value or
* destroy the element it points to, then APR_RING_FOREACH
* will have no way to find out what element to use for its next
* iteration. The reason for this can be seen by looking closely
* at the equivalent loops given in the tip above. So, for example,
* if you are writing a loop that empties out a ring one element
* at a time, APR_RING_FOREACH just won't work for you. Do it
* by hand, like so:
*
* while (!APR_RING_EMPTY(hp, elem, link)) {
* ep = APR_RING_FIRST(hp);
* ...
* APR_RING_REMOVE(ep, link);
* }
*
*/
#define APR_RING_FOREACH(ep, hp, elem, link) \
for ((ep) = APR_RING_FIRST((hp)); \
(ep) != APR_RING_SENTINEL((hp), elem, link); \
(ep) = APR_RING_NEXT((ep), link))
/**
* Iterate through a ring backwards
* @param ep The current element
* @param hp The ring to iterate over
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
* @see APR_RING_FOREACH
*/
#define APR_RING_FOREACH_REVERSE(ep, hp, elem, link) \
for ((ep) = APR_RING_LAST((hp)); \
(ep) != APR_RING_SENTINEL((hp), elem, link); \
(ep) = APR_RING_PREV((ep), link))
/* Debugging tools: */
#ifdef APR_RING_DEBUG
#include
#define APR_RING_CHECK_ONE(msg, ptr) \
fprintf(stderr, "*** %s %p\n", msg, ptr)
#define APR_RING_CHECK(hp, elem, link, msg) \
APR_RING_CHECK_ELEM(APR_RING_SENTINEL(hp, elem, link), elem, link, msg)
#define APR_RING_CHECK_ELEM(ep, elem, link, msg) do { \
struct elem *start = (ep); \
struct elem *this = start; \
fprintf(stderr, "*** ring check start -- %s\n", msg); \
do { \
fprintf(stderr, "\telem %p\n", this); \
fprintf(stderr, "\telem->next %p\n", \
APR_RING_NEXT(this, link)); \
fprintf(stderr, "\telem->prev %p\n", \
APR_RING_PREV(this, link)); \
fprintf(stderr, "\telem->next->prev %p\n", \
APR_RING_PREV(APR_RING_NEXT(this, link), link)); \
fprintf(stderr, "\telem->prev->next %p\n", \
APR_RING_NEXT(APR_RING_PREV(this, link), link)); \
if (APR_RING_PREV(APR_RING_NEXT(this, link), link) != this) { \
fprintf(stderr, "\t*** this->next->prev != this\n"); \
break; \
} \
if (APR_RING_NEXT(APR_RING_PREV(this, link), link) != this) { \
fprintf(stderr, "\t*** this->prev->next != this\n"); \
break; \
} \
this = APR_RING_NEXT(this, link); \
} while (this != start); \
fprintf(stderr, "*** ring check end\n"); \
} while (0)
#else
/**
* Print a single pointer value to STDERR
* (This is a no-op unless APR_RING_DEBUG is defined.)
* @param msg Descriptive message
* @param ptr Pointer value to print
*/
#define APR_RING_CHECK_ONE(msg, ptr)
/**
* Dump all ring pointers to STDERR, starting with the head and looping all
* the way around the ring back to the head. Aborts if an inconsistency
* is found.
* (This is a no-op unless APR_RING_DEBUG is defined.)
* @param hp 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
* @param msg Descriptive message
*/
#define APR_RING_CHECK(hp, elem, link, msg)
/**
* Dump all ring pointers to STDERR, starting with the given element and
* looping all the way around the ring back to that element. Aborts if
* an inconsistency is found.
* (This is a no-op unless APR_RING_DEBUG is defined.)
* @param ep The element
* @param elem The name of the element struct
* @param link The name of the APR_RING_ENTRY in the element struct
* @param msg Descriptive message
*/
#define APR_RING_CHECK_ELEM(ep, elem, link, msg)
#endif
/** @} */
#endif /* !APR_RING_H */