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/* Copyright 2000-2005 The Apache Software Foundation or its licensors, as
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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* This code draws heavily from the 4.4BSD <sys/queue.h> macros
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* and Dean Gaudet's "splim/ring.h".
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* <http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/sys/queue.h>
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* <http://www.arctic.org/~dean/splim/>
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* We'd use Dean's code directly if we could guarantee the
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* availability of inline functions.
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#include "apr_general.h"
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* @defgroup apr_ring Ring Macro Implementations
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* A ring is a kind of doubly-linked list that can be manipulated
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* without knowing where its head is.
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* A ring element struct is linked to the other elements in the ring
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* through its ring entry field, e.g.
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* struct my_element_t {
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* APR_RING_ENTRY(my_element_t) link;
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* An element struct may be put on more than one ring if it has more
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* than one APR_RING_ENTRY field. Each APR_RING_ENTRY has a corresponding
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* APR_RING_HEAD declaration.
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* @warning For strict C standards compliance you should put the APR_RING_ENTRY
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* first in the element struct unless the head is always part of a larger
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* object with enough earlier fields to accommodate the offsetof() used
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* to compute the ring sentinel below. You can usually ignore this caveat.
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#define APR_RING_ENTRY(elem) \
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* Each ring is managed via its head, which is a struct declared like this:
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* APR_RING_HEAD(my_ring_t, my_element_t);
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* struct my_ring_t ring, *ringp;
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* This struct looks just like the element link struct so that we can
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* be sure that the typecasting games will work as expected.
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* The first element in the ring is next after the head, and the last
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* element is just before the head.
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#define APR_RING_HEAD(head, elem) \
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* This is the magic pointer value that occurs before the first and
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* after the last elements in the ring, computed from the address of
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* the ring's head. The head itself isn't an element, but in order to
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* get rid of all the special cases when dealing with the ends of the
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* ring, we play typecasting games to make it look like one.
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* Here is a diagram to illustrate the arrangements of the next and
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* prev pointers of each element in a single ring. Note that they point
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* to the start of each element, not to the APR_RING_ENTRY structure.
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* +->+------+<-+ +->+------+<-+ +->+------+<-+
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* | |struct| | | |struct| | | |struct| |
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* / | elem | \/ | elem | \/ | elem | \
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* ... | | /\ | | /\ | | ...
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* +------+ | | +------+ | | +------+
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* ...--|prev | | +--|ring | | +--|prev |
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* | next|--+ | entry|--+ | next|--...
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* +------+ +------+ +------+
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* | etc. | | etc. | | etc. |
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* The APR_RING_HEAD is nothing but a bare APR_RING_ENTRY. The prev
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* and next pointers in the first and last elements don't actually
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* point to the head, they point to a phantom place called the
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* sentinel. Its value is such that last->next->next == first because
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* the offset from the sentinel to the head's next pointer is the same
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* as the offset from the start of an element to its next pointer.
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* This also works in the opposite direction.
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* +->+------+<-+ +->sentinel<-+ +->+------+<-+
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* | |struct| | | | | |struct| |
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* / | elem | \/ \/ | elem | \
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* ... | | /\ /\ | | ...
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* +------+ | | +------+ | | +------+
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* ...--|prev | | +--|ring | | +--|prev |
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* | next|--+ | head|--+ | next|--...
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* +------+ +------+ +------+
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* Note that the offset mentioned above is different for each kind of
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* ring that the element may be on, and each kind of ring has a unique
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* name for its APR_RING_ENTRY in each element, and has its own type
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* for its APR_RING_HEAD.
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* Note also that if the offset is non-zero (which is required if an
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* element has more than one APR_RING_ENTRY), the unreality of the
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* sentinel may have bad implications on very perverse implementations
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* of C -- see the warning in APR_RING_ENTRY.
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* @param hp The head of the ring
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_SENTINEL(hp, elem, link) \
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(struct elem *)((char *)(hp) - APR_OFFSETOF(struct elem, link))
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* The first element of the ring
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* @param hp The head of the ring
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#define APR_RING_FIRST(hp) (hp)->next
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* The last element of the ring
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* @param hp The head of the ring
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#define APR_RING_LAST(hp) (hp)->prev
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* The next element in the ring
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* @param ep The current element
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_NEXT(ep, link) (ep)->link.next
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* The previous element in the ring
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* @param ep The current element
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_PREV(ep, link) (ep)->link.prev
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* @param hp The head of the ring
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_INIT(hp, elem, link) do { \
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APR_RING_FIRST((hp)) = APR_RING_SENTINEL((hp), elem, link); \
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APR_RING_LAST((hp)) = APR_RING_SENTINEL((hp), elem, link); \
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* Determine if a ring is empty
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* @param hp The head of the ring
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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* @return true or false
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#define APR_RING_EMPTY(hp, elem, link) \
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(APR_RING_FIRST((hp)) == APR_RING_SENTINEL((hp), elem, link))
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* Initialize a singleton element
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* @param ep The element
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_ELEM_INIT(ep, link) do { \
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APR_RING_NEXT((ep), link) = (ep); \
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APR_RING_PREV((ep), link) = (ep); \
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* Splice the sequence ep1..epN into the ring before element lep
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* (..lep.. becomes ..ep1..epN..lep..)
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* @warning This doesn't work for splicing before the first element or on
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* empty rings... see APR_RING_SPLICE_HEAD for one that does
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* @param lep Element in the ring to splice before
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* @param ep1 First element in the sequence to splice in
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* @param epN Last element in the sequence to splice in
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_SPLICE_BEFORE(lep, ep1, epN, link) do { \
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APR_RING_NEXT((epN), link) = (lep); \
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APR_RING_PREV((ep1), link) = APR_RING_PREV((lep), link); \
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APR_RING_NEXT(APR_RING_PREV((lep), link), link) = (ep1); \
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APR_RING_PREV((lep), link) = (epN); \
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* Splice the sequence ep1..epN into the ring after element lep
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* (..lep.. becomes ..lep..ep1..epN..)
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* @warning This doesn't work for splicing after the last element or on
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* empty rings... see APR_RING_SPLICE_TAIL for one that does
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* @param lep Element in the ring to splice after
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* @param ep1 First element in the sequence to splice in
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* @param epN Last element in the sequence to splice in
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_SPLICE_AFTER(lep, ep1, epN, link) do { \
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APR_RING_PREV((ep1), link) = (lep); \
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APR_RING_NEXT((epN), link) = APR_RING_NEXT((lep), link); \
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APR_RING_PREV(APR_RING_NEXT((lep), link), link) = (epN); \
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APR_RING_NEXT((lep), link) = (ep1); \
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* Insert the element nep into the ring before element lep
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* (..lep.. becomes ..nep..lep..)
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* @warning This doesn't work for inserting before the first element or on
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* empty rings... see APR_RING_INSERT_HEAD for one that does
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* @param lep Element in the ring to insert before
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* @param nep Element to insert
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_INSERT_BEFORE(lep, nep, link) \
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APR_RING_SPLICE_BEFORE((lep), (nep), (nep), link)
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* Insert the element nep into the ring after element lep
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* (..lep.. becomes ..lep..nep..)
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* @warning This doesn't work for inserting after the last element or on
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* empty rings... see APR_RING_INSERT_TAIL for one that does
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* @param lep Element in the ring to insert after
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* @param nep Element to insert
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_INSERT_AFTER(lep, nep, link) \
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APR_RING_SPLICE_AFTER((lep), (nep), (nep), link)
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* Splice the sequence ep1..epN into the ring before the first element
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* (..hp.. becomes ..hp..ep1..epN..)
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* @param hp Head of the ring
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* @param ep1 First element in the sequence to splice in
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* @param epN Last element in the sequence to splice in
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_SPLICE_HEAD(hp, ep1, epN, elem, link) \
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APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((hp), elem, link), \
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* Splice the sequence ep1..epN into the ring after the last element
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* (..hp.. becomes ..ep1..epN..hp..)
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* @param hp Head of the ring
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* @param ep1 First element in the sequence to splice in
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* @param epN Last element in the sequence to splice in
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_SPLICE_TAIL(hp, ep1, epN, elem, link) \
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APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((hp), elem, link), \
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* Insert the element nep into the ring before the first element
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* (..hp.. becomes ..hp..nep..)
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* @param hp Head of the ring
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* @param nep Element to insert
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_INSERT_HEAD(hp, nep, elem, link) \
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APR_RING_SPLICE_HEAD((hp), (nep), (nep), elem, link)
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* Insert the element nep into the ring after the last element
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* (..hp.. becomes ..nep..hp..)
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* @param hp Head of the ring
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* @param nep Element to insert
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_INSERT_TAIL(hp, nep, elem, link) \
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APR_RING_SPLICE_TAIL((hp), (nep), (nep), elem, link)
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* Concatenate ring h2 onto the end of ring h1, leaving h2 empty.
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* @param h1 Head of the ring to concatenate onto
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* @param h2 Head of the ring to concatenate
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_CONCAT(h1, h2, elem, link) do { \
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if (!APR_RING_EMPTY((h2), elem, link)) { \
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APR_RING_SPLICE_BEFORE(APR_RING_SENTINEL((h1), elem, link), \
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APR_RING_FIRST((h2)), \
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APR_RING_LAST((h2)), link); \
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APR_RING_INIT((h2), elem, link); \
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* Prepend ring h2 onto the beginning of ring h1, leaving h2 empty.
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* @param h1 Head of the ring to prepend onto
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* @param h2 Head of the ring to prepend
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_PREPEND(h1, h2, elem, link) do { \
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if (!APR_RING_EMPTY((h2), elem, link)) { \
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APR_RING_SPLICE_AFTER(APR_RING_SENTINEL((h1), elem, link), \
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APR_RING_FIRST((h2)), \
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APR_RING_LAST((h2)), link); \
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APR_RING_INIT((h2), elem, link); \
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* Unsplice a sequence of elements from a ring
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* @warning The unspliced sequence is left with dangling pointers at either end
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* @param ep1 First element in the sequence to unsplice
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* @param epN Last element in the sequence to unsplice
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_UNSPLICE(ep1, epN, link) do { \
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APR_RING_NEXT(APR_RING_PREV((ep1), link), link) = \
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APR_RING_NEXT((epN), link); \
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APR_RING_PREV(APR_RING_NEXT((epN), link), link) = \
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APR_RING_PREV((ep1), link); \
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* Remove a single element from a ring
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* @warning The unspliced element is left with dangling pointers at either end
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* @param ep Element to remove
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_REMOVE(ep, link) \
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APR_RING_UNSPLICE((ep), (ep), link)
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/* Debugging tools: */
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#ifdef APR_RING_DEBUG
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#define APR_RING_CHECK_ONE(msg, ptr) \
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fprintf(stderr, "*** %s %p\n", msg, ptr)
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#define APR_RING_CHECK(hp, elem, link, msg) \
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APR_RING_CHECK_ELEM(APR_RING_SENTINEL(hp, elem, link), elem, link, msg)
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#define APR_RING_CHECK_ELEM(ep, elem, link, msg) do { \
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struct elem *start = (ep); \
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struct elem *here = start; \
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fprintf(stderr, "*** ring check start -- %s\n", msg); \
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fprintf(stderr, "\telem %p\n", here); \
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fprintf(stderr, "\telem->next %p\n", \
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APR_RING_NEXT(here, link)); \
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fprintf(stderr, "\telem->prev %p\n", \
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APR_RING_PREV(here, link)); \
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fprintf(stderr, "\telem->next->prev %p\n", \
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APR_RING_PREV(APR_RING_NEXT(here, link), link)); \
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fprintf(stderr, "\telem->prev->next %p\n", \
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APR_RING_NEXT(APR_RING_PREV(here, link), link)); \
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if (APR_RING_PREV(APR_RING_NEXT(here, link), link) != here) { \
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fprintf(stderr, "\t*** elem->next->prev != elem\n"); \
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if (APR_RING_NEXT(APR_RING_PREV(here, link), link) != here) { \
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fprintf(stderr, "\t*** elem->prev->next != elem\n"); \
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here = APR_RING_NEXT(here, link); \
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} while (here != start); \
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fprintf(stderr, "*** ring check end\n"); \
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#define APR_RING_CHECK_CONSISTENCY(hp, elem, link) \
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APR_RING_CHECK_ELEM_CONSISTENCY(APR_RING_SENTINEL(hp, elem, link),\
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#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link) do { \
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struct elem *start = (ep); \
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struct elem *here = start; \
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assert(APR_RING_PREV(APR_RING_NEXT(here, link), link) == here); \
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assert(APR_RING_NEXT(APR_RING_PREV(here, link), link) == here); \
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here = APR_RING_NEXT(here, link); \
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} while (here != start); \
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* Print a single pointer value to STDERR
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* (This is a no-op unless APR_RING_DEBUG is defined.)
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* @param msg Descriptive message
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* @param ptr Pointer value to print
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#define APR_RING_CHECK_ONE(msg, ptr)
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* Dump all ring pointers to STDERR, starting with the head and looping all
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* the way around the ring back to the head. Aborts if an inconsistency
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* (This is a no-op unless APR_RING_DEBUG is defined.)
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* @param hp Head of the ring
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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* @param msg Descriptive message
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#define APR_RING_CHECK(hp, elem, link, msg)
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* Loops around a ring and checks all the pointers for consistency. Pops
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* an assertion if any inconsistency is found. Same idea as APR_RING_CHECK()
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* except that it's silent if all is well.
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* (This is a no-op unless APR_RING_DEBUG is defined.)
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* @param hp Head of the ring
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_CHECK_CONSISTENCY(hp, elem, link)
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* Dump all ring pointers to STDERR, starting with the given element and
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* looping all the way around the ring back to that element. Aborts if
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* an inconsistency is found.
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* (This is a no-op unless APR_RING_DEBUG is defined.)
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* @param ep The element
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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* @param msg Descriptive message
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#define APR_RING_CHECK_ELEM(ep, elem, link, msg)
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* Loops around a ring, starting with the given element, and checks all
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* the pointers for consistency. Pops an assertion if any inconsistency
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* is found. Same idea as APR_RING_CHECK_ELEM() except that it's silent
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* (This is a no-op unless APR_RING_DEBUG is defined.)
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* @param ep The element
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* @param elem The name of the element struct
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* @param link The name of the APR_RING_ENTRY in the element struct
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#define APR_RING_CHECK_ELEM_CONSISTENCY(ep, elem, link)
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#endif /* !APR_RING_H */
added
removed
srclib/apr/include/apr_ring.h
