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/* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
* 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
/**
* @file apr_ring.h
* @brief APR Rings
*/
/*
* for offsetof()
*/
#include "apr_general.h"
/**
* @defgroup apr_ring Ring Macro Implementations
* @ingroup APR
* 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.
* <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. Each APR_RING_ENTRY has a corresponding
* APR_RING_HEAD declaration.
*
* @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 * volatile next; \
struct elem * volatile prev; \
}
/**
* The Ring Head
*
* 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.
*/
#define APR_RING_HEAD(head, elem) \
struct head { \
struct elem * volatile next; \
struct elem * volatile 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.
*
* Here is a diagram to illustrate the arrangements of the next and
* prev pointers of each element in a single ring. Note that they point
* to the start of each element, not to the APR_RING_ENTRY structure.
*
* <pre>
* +->+------+<-+ +->+------+<-+ +->+------+<-+
* | |struct| | | |struct| | | |struct| |
* / | elem | \/ | elem | \/ | elem | \
* ... | | /\ | | /\ | | ...
* +------+ | | +------+ | | +------+
* ...--|prev | | +--|ring | | +--|prev |
* | next|--+ | entry|--+ | next|--...
* +------+ +------+ +------+
* | etc. | | etc. | | etc. |
* : : : : : :
* </pre>
*
* The APR_RING_HEAD is nothing but a bare APR_RING_ENTRY. The prev
* and next pointers in the first and last elements don't actually
* point to the head, they point to a phantom place called the
* sentinel. Its value is such that last->next->next == first because
* the offset from the sentinel to the head's next pointer is the same
* as the offset from the start of an element to its next pointer.
* This also works in the opposite direction.
*
* <pre>
* last first
* +->+------+<-+ +->sentinel<-+ +->+------+<-+
* | |struct| | | | | |struct| |
* / | elem | \/ \/ | elem | \
* ... | | /\ /\ | | ...
* +------+ | | +------+ | | +------+
* ...--|prev | | +--|ring | | +--|prev |
* | next|--+ | head|--+ | next|--...
* +------+ +------+ +------+
* | etc. | | etc. |
* : : : :
* </pre>
*
* Note that the offset mentioned above is different for each kind of
* ring that the element may be on, and each kind of ring has a unique
* name for its APR_RING_ENTRY in each element, and has its own type
* for its APR_RING_HEAD.
*
* Note also that if the offset is non-zero (which is required if an
* element has more than one APR_RING_ENTRY), the unreality of the
* sentinel may have bad implications on very perverse implementations
* of C -- see the warning in APR_RING_ENTRY.
*
* @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)->next) - APR_OFFSETOF(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 over a ring
* @param ep The current element
* @param head 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_FOREACH(ep, head, elem, link) \
for (ep = APR_RING_FIRST(head); \
ep != APR_RING_SENTINEL(head, elem, link); \
ep = APR_RING_NEXT(ep, link))
/**
* Iterate over a ring safe against removal of the current element
* @param ep1 The current element
* @param ep2 Iteration cursor
* @param head 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_FOREACH_SAFE(ep1, ep2, head, elem, link) \
for (ep1 = APR_RING_FIRST(head), ep2 = APR_RING_NEXT(ep1, link); \
ep1 != APR_RING_SENTINEL(head, elem, link); \
ep1 = ep2, ep2 = APR_RING_NEXT(ep1, link))
/* Debugging tools: */
#ifdef APR_RING_DEBUG
#include <stdio.h>
#include <assert.h>
#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 *here = start; \
fprintf(stderr, "*** ring check start -- %s\n", msg); \
do { \
fprintf(stderr, "\telem %p\n", here); \
fprintf(stderr, "\telem->next %p\n", \
APR_RING_NEXT(here, link)); \
fprintf(stderr, "\telem->prev %p\n", \
APR_RING_PREV(here, link)); \
fprintf(stderr, "\telem->next->prev %p\n", \
APR_RING_PREV(APR_RING_NEXT(here, link), link)); \
fprintf(stderr, "\telem->prev->next %p\n", \
APR_RING_NEXT(APR_RING_PREV(here, link), link)); \
if (APR_RING_PREV(APR_RING_NEXT(here, link), link) != here) { \
fprintf(stderr, "\t*** elem->next->prev != elem\n"); \
break; \
} \
if (APR_RING_NEXT(APR_RING_PREV(here, link), link) != here) { \
fprintf(stderr, "\t*** elem->prev->next != elem\n"); \
break; \
} \
here = APR_RING_NEXT(here, link); \
} while (here != start); \
fprintf(stderr, "*** ring check end\n"); \
} while (0)
#define APR_RING_CHECK_CONSISTENCY(hp, elem, link) \
APR_RING_CHECK_ELEM_CONSISTENCY(APR_RING_SENTINEL(hp, elem, link),\
elem, link)
#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link) do { \
struct elem *start = (ep); \
struct elem *here = start; \
do { \
assert(APR_RING_PREV(APR_RING_NEXT(here, link), link) == here); \
assert(APR_RING_NEXT(APR_RING_PREV(here, link), link) == here); \
here = APR_RING_NEXT(here, link); \
} while (here != start); \
} 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)
/**
* Loops around a ring and checks all the pointers for consistency. Pops
* an assertion if any inconsistency is found. Same idea as APR_RING_CHECK()
* except that it's silent if all is well.
* (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
*/
#define APR_RING_CHECK_CONSISTENCY(hp, elem, link)
/**
* 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)
/**
* Loops around a ring, starting with the given element, and checks all
* the pointers for consistency. Pops an assertion if any inconsistency
* is found. Same idea as APR_RING_CHECK_ELEM() except that it's silent
* if all is well.
* (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
*/
#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link)
#endif
/** @} */
#endif /* !APR_RING_H */
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