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 /* SPDX-License-Identifier: BSD-2-Clause */
 
 /**
  * @file
  *
  * @ingroup RTEMSScoreChain
  *
  * @brief This header file provides interfaces of the
  *   @ref RTEMSScoreChain which are only used by the implementation.
  */
 
 /*
  *  Copyright (c) 2010 embedded brains GmbH & Co. KG
  *
  *  COPYRIGHT (c) 1989-2014.
  *  On-Line Applications Research Corporation (OAR).
  *
  * 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.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
  */
 
 #ifndef _RTEMS_SCORE_CHAINIMPL_H
 #define _RTEMS_SCORE_CHAINIMPL_H
 
 #include <rtems/score/chain.h>
 #include <rtems/score/assert.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /**
  * @addtogroup RTEMSScoreChain
  *
  * @{
  */
 
 /**
  *  @brief Chain initializer for an empty chain with designator @a name.
  */
 #define CHAIN_INITIALIZER_EMPTY(name) \
   { { { &(name).Tail.Node, NULL }, &(name).Head.Node } }
 
 /**
  *  @brief Chain initializer for a chain with one @a node.
  *
  *  @see CHAIN_NODE_INITIALIZER_ONE_NODE_CHAIN().
  */
 #define CHAIN_INITIALIZER_ONE_NODE( node ) \
   { { { (node), NULL }, (node) } }
 
 /**
  *  @brief Chain node initializer for a @a chain containing exactly this node.
  *
  *  @see CHAIN_INITIALIZER_ONE_NODE().
  */
 #define CHAIN_NODE_INITIALIZER_ONE_NODE_CHAIN( chain ) \
   { &(chain)->Tail.Node, &(chain)->Head.Node }
 
 /**
  *  @brief Chain definition for an empty chain with designator @a name.
  */
 #define CHAIN_DEFINE_EMPTY(name) \
   Chain_Control name = CHAIN_INITIALIZER_EMPTY(name)
 
 /**
  *  @brief Initializes a chain header.
  *
  *  This routine initializes @a the_chain structure to manage the
  *  contiguous array of @a number_nodes nodes which starts at
  *  @a starting_address.  Each node is of @a node_size bytes.
  *
  *  @param[out] the_chain Specifies the chain to initialize.
  *  @param starting_address The starting address of the array
  *         of elements.
  *  @param number_nodes The number of nodes that will be in the chain.
  *  @param node_size The size of each node.
  */
 void _Chain_Initialize(
   Chain_Control *the_chain,
   void          *starting_address,
   size_t         number_nodes,
   size_t         node_size
 );
 
 /**
  * @brief Returns the node count of the chain.
  *
  * @param chain The chain to return the node count from.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  * operation.
  *
  * @return The node count of the chain.
  */
 size_t _Chain_Node_count_unprotected( const Chain_Control *chain );
 
 /**
  * @brief Sets off chain.
  *
  * This function sets the next field of the @a node to NULL indicating the @a
  * node is not part of a chain.
  *
  * @param[out] node The node to set off chain.
  */
 static inline void _Chain_Set_off_chain(
   Chain_Node *node
 )
 {
   node->next = NULL;
 #if defined(RTEMS_DEBUG)
   node->previous = NULL;
 #endif
 }
 
 /**
  * @brief Initializes a chain node.
  *
  * In debug configurations, the node is set off chain.  In all other
  * configurations, this function does nothing.
  *
  * @param[out] the_node The chain node to initialize.
  */
 static inline void _Chain_Initialize_node( Chain_Node *the_node )
 {
 #if defined(RTEMS_DEBUG)
   _Chain_Set_off_chain( the_node );
 #else
   (void) the_node;
 #endif
 }
 
 /**
  * @brief Checks if the node is off chain.
  *
  * This function returns true if the @a node is not on a chain.  A @a node is
  * off chain if the next field is set to NULL.
  *
  * @param node The node to check if it is off chain.
  *
  * @retval true The @a node is off chain.
  * @retval false The @a node is not off chain.
  */
 static inline bool _Chain_Is_node_off_chain(
   const Chain_Node *node
 )
 {
   return node->next == NULL;
 }
 
 /**
  * @brief Checks if two nodes are equal.
  *
  * This function returns true if @a left and @a right are equal,
  * and false otherwise.
  *
  * @param left The node on the left hand side of the comparison.
  * @param right The node on the right hand side of the comparison.
  *
  * @retval true @a left and @a right are equal.
  * @retval false @a left and @a right are not equal.
  */
 static inline bool _Chain_Are_nodes_equal(
   const Chain_Node *left,
   const Chain_Node *right
 )
 {
   return left == right;
 }
 
 /**
  * @brief Returns pointer to chain head.
  *
  * This function returns a pointer to the head node on the chain.
  *
  * @param[in] the_chain The chain to be operated upon.
  *
  * @return This method returns the permanent head node of the chain.
  */
 static inline Chain_Node *_Chain_Head(
   Chain_Control *the_chain
 )
 {
   return &the_chain->Head.Node;
 }
 
 /**
  * @brief Returns pointer to immutable chain head.
  *
  * This function returns a pointer to the head node on the chain.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the permanent head node of the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_head(
   const Chain_Control *the_chain
 )
 {
   return &the_chain->Head.Node;
 }
 
 /**
  * @brief Returns pointer to chain tail.
  *
  * This function returns a pointer to the tail node on the chain.
  *
  * @param[in] the_chain The chain to be operated upon.
  *
  * @return This method returns the permanent tail node of the chain.
  */
 static inline Chain_Node *_Chain_Tail(
   Chain_Control *the_chain
 )
 {
   return &the_chain->Tail.Node;
 }
 
 /**
  * @brief Returns pointer to immutable chain tail.
  *
  * This function returns a pointer to the tail node on the chain.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the permanent tail node of the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_tail(
   const Chain_Control *the_chain
 )
 {
   return &the_chain->Tail.Node;
 }
 
 /**
  * @brief Returns pointer to chain's first node.
  *
  * This function returns a pointer to the first node on the chain after the
  * head.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the first node of the chain.
  */
 static inline Chain_Node *_Chain_First(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_head( the_chain )->next;
 }
 
 /**
  * @brief Returns pointer to immutable chain's first node.
  *
  * This function returns a pointer to the first node on the chain after the
  * head.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the first node of the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_first(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_head( the_chain )->next;
 }
 
 /**
  * @brief Returns pointer to chain's last node.
  *
  * This function returns a pointer to the last node on the chain just before
  * the tail.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the last node of the chain.
  */
 static inline Chain_Node *_Chain_Last(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_tail( the_chain )->previous;
 }
 
 /**
  * @brief Returns pointer to immutable chain's last node.
  *
  * This function returns a pointer to the last node on the chain just before
  * the tail.
  *
  * @param the_chain The chain to be operated upon.
  *
  * @return This method returns the last node of the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_last(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_tail( the_chain )->previous;
 }
 
 /**
  * @brief Returns pointer to the next node from this node.
  *
  * This function returns a pointer to the next node after this node.
  *
  * @param the_node The node to be operated upon.
  *
  * @return This method returns the next node on the chain.
  */
 static inline Chain_Node *_Chain_Next(
   const Chain_Node *the_node
 )
 {
   return the_node->next;
 }
 
 /**
  * @brief Returns pointer to the immutable next node from this node.
  *
  * This function returns a pointer to the next node after this node.
  *
  * @param the_node The node to be operated upon.
  *
  * @return This method returns the next node on the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_next(
   const Chain_Node *the_node
 )
 {
   return the_node->next;
 }
 
 /**
  * @brief Returns pointer to the previous node from this node.
  *
  * This function returns a pointer to the previous node on this chain.
  *
  * @param the_node The node to be operated upon.
  *
  * @return This method returns the previous node on the chain.
  */
 static inline Chain_Node *_Chain_Previous(
   const Chain_Node *the_node
 )
 {
   return the_node->previous;
 }
 
 /**
  * @brief Returns pointer to the immutable previous node from this node.
  *
  * This function returns a pointer to the previous node on this chain.
  *
  * @param the_node The node to be operated upon.
  *
  * @return This method returns the previous node on the chain.
  */
 static inline const Chain_Node *_Chain_Immutable_previous(
   const Chain_Node *the_node
 )
 {
   return the_node->previous;
 }
 
 /**
  * @brief Checks if the chain is empty.
  *
  * This function returns true if there are no nodes on @a the_chain and
  * false otherwise.
  *
  * @param the_chain The chain to check if it is empty.
  *
  * @retval true There are no nodes on @a the_chain.
  * @retval false There are nodes on @a the_chain.
  */
 static inline bool _Chain_Is_empty(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_first( the_chain )
     == _Chain_Immutable_tail( the_chain );
 }
 
 /**
  * @brief Checks if this is the first node on the chain.
  *
  * This function returns true if the_node is the first node on a chain and
  * false otherwise.
  *
  * @param the_node The node of which the caller wants to know if it is
  *            the first node on a chain.
  *
  * @retval true @a the_node is the first node on a chain.
  * @retval false @a the_node is not the first node on a chain.
  */
 static inline bool _Chain_Is_first(
   const Chain_Node *the_node
 )
 {
   return (the_node->previous->previous == NULL);
 }
 
 /**
  * @brief Checks if this is the last node on the chain.
  *
  * This function returns true if @a the_node is the last node on a chain and
  * false otherwise.
  *
  * @param the_node The node of which the caller wants to know if it is
  *            the last node on a chain.
  *
  * @retval true @a the_node is the last node on a chain.
  * @retval false @a the_node is not the last node on a chain.
  */
 static inline bool _Chain_Is_last(
   const Chain_Node *the_node
 )
 {
   return (the_node->next->next == NULL);
 }
 
 /**
  * @brief Checks if this chain has only one node.
  *
  * This function returns true if there is only one node on @a the_chain and
  * false otherwise.
  *
  * @param the_chain is the chain to be operated upon.
  *
  * @retval true There is only one node on @a the_chain.
  * @retval false There is more than one node on @a the_chain.
  */
 static inline bool _Chain_Has_only_one_node(
   const Chain_Control *the_chain
 )
 {
   return _Chain_Immutable_first( the_chain )
     == _Chain_Immutable_last( the_chain );
 }
 
 /**
  * @brief Checks if this node is the chain head.
  *
  * This function returns true if @a the_node is the head of @a the_chain and
  * false otherwise.
  *
  * @param the_chain The chain to be operated upon.
  * @param the_node The node to check for being the Chain Head.
  *
  * @retval true @a the_node is the head of @a the_chain.
  * @retval false @a the_node is not the head of @a the_chain.
  */
 static inline bool _Chain_Is_head(
   const Chain_Control *the_chain,
   const Chain_Node    *the_node
 )
 {
   return (the_node == _Chain_Immutable_head( the_chain ));
 }
 
 /**
  * @brief Checks if this node is the chain tail.
  *
  * This function returns true if @a the_node is the tail of @a the_chain and
  * false otherwise.
  *
  * @param the_chain The chain to be operated upon.
  * @param the_node The node to check for being the Chain Tail.
  *
  * @retval true @a the_node is the tail of @a the_chain.
  * @retval false @a the_node is not the tail of @a the_chain.
  */
 static inline bool _Chain_Is_tail(
   const Chain_Control *the_chain,
   const Chain_Node    *the_node
 )
 {
   return (the_node == _Chain_Immutable_tail( the_chain ));
 }
 
 /**
  * @brief Initializes this chain as empty.
  *
  * This routine initializes the specified chain to contain zero nodes.
  *
  * @param[out] the_chain The chain to be initialized.
  */
 static inline void _Chain_Initialize_empty(
   Chain_Control *the_chain
 )
 {
   Chain_Node *head;
   Chain_Node *tail;
 
   _Assert( the_chain != NULL );
 
   head = _Chain_Head( the_chain );
   tail = _Chain_Tail( the_chain );
 
   head->next = tail;
   head->previous = NULL;
   tail->previous = head;
 }
 
 /**
  * @brief Initializes this chain to contain exactly the specified node.
  *
  * @param[out] the_chain The chain to be initialized to contain exactly the specified node.
  * @param[out] the_node The one and only node of the chain to be initialized.
  */
 static inline void _Chain_Initialize_one(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   Chain_Node *head;
   Chain_Node *tail;
 
   _Assert( _Chain_Is_node_off_chain( the_node ) );
 
   head = _Chain_Head( the_chain );
   tail = _Chain_Tail( the_chain );
 
   the_node->next = tail;
   the_node->previous = head;
 
   head->next = the_node;
   head->previous = NULL;
   tail->previous = the_node;
 }
 
 /**
  * @brief Extracts this node (unprotected).
  *
  * This routine extracts the_node from the chain on which it resides.
  * It does NOT disable interrupts to ensure the atomicity of the
  * extract operation.
  *
  * @param[out] the_node The node to be extracted.
  */
 static inline void _Chain_Extract_unprotected(
   Chain_Node *the_node
 )
 {
   Chain_Node *next;
   Chain_Node *previous;
 
   _Assert( !_Chain_Is_node_off_chain( the_node ) );
 
   next           = the_node->next;
   previous       = the_node->previous;
   next->previous = previous;
   previous->next = next;
 
 #if defined(RTEMS_DEBUG)
   _Chain_Set_off_chain( the_node );
 #endif
 }
 
 /**
  * @brief Gets the first node (unprotected).
  *
  * This function removes the first node from the_chain and returns
  * a pointer to that node.  It does NOT disable interrupts to ensure
  * the atomicity of the get operation.
  *
  * @param[in, out] the_chain The chain to attempt to get the first node from.
  *
  * @return This method returns the first node on the chain even if it is
  *         the Chain Tail.
  *
  * @note This routine assumes that there is at least one node on the chain
  *       and always returns a node even if it is the Chain Tail.
  */
 static inline Chain_Node *_Chain_Get_first_unprotected(
   Chain_Control *the_chain
 )
 {
   Chain_Node *head;
   Chain_Node *old_first;
   Chain_Node *new_first;
 
   _Assert( !_Chain_Is_empty( the_chain ) );
 
   head = _Chain_Head( the_chain );
   old_first = head->next;
   new_first = old_first->next;
 
   head->next = new_first;
   new_first->previous = head;
 
 #if defined(RTEMS_DEBUG)
   _Chain_Set_off_chain( old_first );
 #endif
 
   return old_first;
 }
 
 /**
  * @brief Gets the first node (unprotected).
  *
  * This function removes the first node from the_chain and returns
  * a pointer to that node.  If the_chain is empty, then NULL is returned.
  *
  * @param[in, out] the_chain The chain to attempt to get the first node from.
  *
  * @retval pointer Pointer to the first node.  The chain contained at least one node.
  * @retval NULL The chain is empty.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       get operation.
  */
 static inline Chain_Node *_Chain_Get_unprotected(
   Chain_Control *the_chain
 )
 {
   if ( !_Chain_Is_empty(the_chain))
     return _Chain_Get_first_unprotected(the_chain);
   else
     return NULL;
 }
 
 /**
  * @brief Inserts a node (unprotected).
  *
  * This routine inserts the_node on a chain immediately following
  * after_node.
  *
  * @param[in, out] after_node The node which will precede @a the_node on the
  *            chain.
  * @param[out] the_node The node to be inserted after @a after_node.
  *
  * @note It does NOT disable interrupts to ensure the atomicity
  *       of the extract operation.
  */
 static inline void _Chain_Insert_unprotected(
   Chain_Node *after_node,
   Chain_Node *the_node
 )
 {
   Chain_Node *before_node;
 
   _Assert( _Chain_Is_node_off_chain( the_node ) );
 
   the_node->previous    = after_node;
   before_node           = after_node->next;
   after_node->next      = the_node;
   the_node->next        = before_node;
   before_node->previous = the_node;
 }
 
 /**
  * @brief Appends a node (unprotected).
  *
  * This routine appends the_node onto the end of the_chain.
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[out] the_node The node to be appended to the end of @a the_chain.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       append operation.
  */
 static inline void _Chain_Append_unprotected(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   Chain_Node *tail;
   Chain_Node *old_last;
 
   _Assert( _Chain_Is_node_off_chain( the_node ) );
 
   tail = _Chain_Tail( the_chain );
   old_last = tail->previous;
 
   the_node->next = tail;
   tail->previous = the_node;
   old_last->next = the_node;
   the_node->previous = old_last;
 }
 
 /**
  * @brief Appends a node on the end of a chain if the node is in the off chain
  * state (unprotected).
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[in, out] the_node The node to be appended if it is in the off chain.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       append operation.
  *
  * @see _Chain_Append_unprotected() and _Chain_Is_node_off_chain().
  */
 static inline void _Chain_Append_if_is_off_chain_unprotected(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   if ( _Chain_Is_node_off_chain( the_node ) ) {
     _Chain_Append_unprotected( the_chain, the_node );
   }
 }
 
 /**
  * @brief Prepends a node (unprotected).
  *
  * This routine prepends the_node onto the front of the_chain.
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[in, out] the_node The node to be prepended to the front of @a the_chain.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       prepend operation.
  */
 static inline void _Chain_Prepend_unprotected(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   _Chain_Insert_unprotected(_Chain_Head(the_chain), the_node);
 }
 
 /**
  * @brief Appends a node and checks if the chain was empty before (unprotected).
  *
  * This routine appends the_node onto the end of the_chain.
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[out] the_node The node to be appended to the end of @a the_chain.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       append operation.
  *
  * @retval true The chain was empty before.
  * @retval false The chain contained at least one node before.
  */
 static inline bool _Chain_Append_with_empty_check_unprotected(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   bool was_empty = _Chain_Is_empty( the_chain );
 
   _Chain_Append_unprotected( the_chain, the_node );
 
   return was_empty;
 }
 
 /**
  * @brief Prepends a node and checks if the chain was empty before (unprotected).
  *
  * This routine prepends the_node onto the front of the_chain.
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[out] the_node The node to be prepended to the front of @a the_chain.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       prepend operation.
  *
  * @retval true The chain was empty before.
  * @retval false The chain contained at least one node before.
  */
 static inline bool _Chain_Prepend_with_empty_check_unprotected(
   Chain_Control *the_chain,
   Chain_Node    *the_node
 )
 {
   bool was_empty = _Chain_Is_empty( the_chain );
 
   _Chain_Prepend_unprotected( the_chain, the_node );
 
   return was_empty;
 }
 
 /**
  * @brief Gets the first node and checks if the chain is empty afterwards
  * (unprotected).
  *
  * This function removes the first node from the_chain and returns
  * a pointer to that node in @a the_node.  If the_chain is empty, then NULL is
  * returned.
  *
  * @param[in, out] the_chain The chain to attempt to get the first node from.
  * @param[out] the_node The first node on the chain or NULL if the chain is
  * empty.
  *
  * @note It does NOT disable interrupts to ensure the atomicity of the
  *       get operation.
  *
  * @retval true The chain is empty now.
  * @retval false The chain contains at least one node now.
  */
 static inline bool _Chain_Get_with_empty_check_unprotected(
   Chain_Control *the_chain,
   Chain_Node **the_node
 )
 {
   bool is_empty_now = true;
   Chain_Node *head = _Chain_Head( the_chain );
   Chain_Node *tail = _Chain_Tail( the_chain );
   Chain_Node *old_first = head->next;
 
   if ( old_first != tail ) {
     Chain_Node *new_first = old_first->next;
 
     head->next = new_first;
     new_first->previous = head;
 
     *the_node = old_first;
 
     is_empty_now = new_first == tail;
   } else
     *the_node = NULL;
 
   return is_empty_now;
 }
 
 /**
  * @brief Chain node order.
  *
  * @param left The left hand side.
  * @param right The right hand side.
  *
  * @retval true According to the order the left node precedes the right node.
  * @retval false Otherwise.
  */
 typedef bool ( *Chain_Node_order )(
   const void       *key,
   const Chain_Node *left,
   const Chain_Node *right
 );
 
 /**
  * @brief Inserts a node into the chain according to the order relation.
  *
  * After the operation the chain contains the node to insert and the order
  * relation holds for all nodes from the head up to the inserted node.  Nodes
  * after the inserted node are not moved.
  *
  * @param[in, out] the_chain The chain to be operated upon.
  * @param[out] to_insert The node to insert.
  * @param left The left hand side passed to the order relation.  It must
  *   correspond to the node to insert.  The separate left hand side parameter
  *   may help the compiler to generate better code if it is stored in a local
  *   variable.
  * @param order The order relation.
  */
 static inline void _Chain_Insert_ordered_unprotected(
   Chain_Control    *the_chain,
   Chain_Node       *to_insert,
   const void       *key,
   Chain_Node_order  order
 )
 {
   const Chain_Node *tail = _Chain_Immutable_tail( the_chain );
   Chain_Node *previous = _Chain_Head( the_chain );
   Chain_Node *next = _Chain_First( the_chain );
 
   while ( next != tail && !( *order )( key, to_insert, next ) ) {
     previous = next;
     next = _Chain_Next( next );
   }
 
   _Chain_Insert_unprotected( previous, to_insert );
 }
 
 /**
  * @brief The chain iterator direction.
  */
 typedef enum {
   /**
    * @brief Iteration from head to tail.
    */
   CHAIN_ITERATOR_FORWARD,
 
   /**
    * @brief Iteration from tail to head.
    */
   CHAIN_ITERATOR_BACKWARD
 } Chain_Iterator_direction;
 
 /**
  * @brief A chain iterator which is updated during node extraction if it is
  * properly registered.
  *
  * @see _Chain_Iterator_initialize().
  */
 typedef struct {
   /**
    * @brief Node for registration.
    *
    * Used during _Chain_Iterator_initialize() and _Chain_Iterator_destroy().
    */
   Chain_Node Registry_node;
 
   /**
    * @brief The direction of this iterator.
    *
    * Immutable after initialization via _Chain_Iterator_initialize().
    */
   Chain_Iterator_direction  direction;
 
   /**
    * @brief The current position of this iterator.
    *
    * The position is initialized via _Chain_Iterator_initialize().  It must be
    * explicitly set after one valid iteration step, e.g. in case a next node in
    * the iterator direction existed.  It is updated through the registration in
    * case a node is extracted via _Chain_Iterator_registry_update().
    */
   Chain_Node *position;
 } Chain_Iterator;
 
 /**
  * @brief A registry for chain iterators.
  *
  * Should be attached to a chain control to enable safe iteration through a
  * chain in case of concurrent node extractions.
  */
 typedef struct {
   Chain_Control Iterators;
 } Chain_Iterator_registry;
 
 /**
  * @brief Chain iterator registry initializer for static initialization.
  *
  * @param name The designator of the chain iterator registry.
  */
 #define CHAIN_ITERATOR_REGISTRY_INITIALIZER( name ) \
   { CHAIN_INITIALIZER_EMPTY( name.Iterators ) }
 
 /**
  * @brief Initializes a chain iterator registry.
  *
  * @param[out] the_registry The chain iterator registry to be initialized.
  */
 static inline void _Chain_Iterator_registry_initialize(
   Chain_Iterator_registry *the_registry
 )
 {
   _Chain_Initialize_empty( &the_registry->Iterators );
 }
 
 /**
  * @brief Updates all iterators present in the chain iterator registry in case
  * of a node extraction.
  *
  * Must be called before _Chain_Extract_unprotected().
  *
  * @warning This function will look at all registered chain iterators to
  *   determine if an update is necessary.
  *
  * @param[in, out] the_registry the chain iterator registry.
  * @param[out] the_node_to_extract The node that will be extracted.
  */
 static inline void _Chain_Iterator_registry_update(
   Chain_Iterator_registry *the_registry,
   Chain_Node              *the_node_to_extract
 )
 {
   Chain_Node *iter_node;
   Chain_Node *iter_tail;
 
   iter_node = _Chain_Head( &the_registry->Iterators );
   iter_tail = _Chain_Tail( &the_registry->Iterators );
 
   while ( ( iter_node = _Chain_Next( iter_node ) ) != iter_tail ) {
     Chain_Iterator *iter;
 
     iter = (Chain_Iterator *) iter_node;
 
     if ( iter->position == the_node_to_extract ) {
       if ( iter->direction == CHAIN_ITERATOR_FORWARD ) {
         iter->position = _Chain_Previous( the_node_to_extract );
       } else {
         iter->position = _Chain_Next( the_node_to_extract );
       }
     }
   }
 }
 
 /**
  * @brief Initializes the chain iterator.
  *
  * In the following example nodes inserted during the iteration are visited in
  * case they are inserted after the current position in iteration order.
  *
  * @code
  * #include <rtems/score/chainimpl.h>
  * #include <rtems/score/isrlock.h>
  *
  * typedef struct {
  *   Chain_Control           Chain;
  *   Chain_Iterator_registry Iterators;
  * #if ISR_LOCK_NEEDS_OBJECT
  *   ISR_lock_Control        Lock;
  * #endif
  * } Some_Control;
  *
  * void iterate(
  *   Some_Control   *the_some,
  *   void         ( *visitor )( Chain_Node * )
  * )
  * {
  *   ISR_lock_Context  lock_context;
  *   Chain_Iterator    iter;
  *   Chain_Node       *node;
  *   const Chain_Node *end;
  *
  *   end = _Chain_Immutable_tail( &the_some->Chain );
  *
  *   _ISR_lock_ISR_disable_and_acquire( &the_some->Lock, &lock_context );
  *
  *   _Chain_Iterator_initialize(
  *     &the_some->Chain,
  *     &the_some->Iterators,
  *     &iter,
  *     CHAIN_ITERATOR_FORWARD
  *   );
  *
  *   while ( ( node = _Chain_Iterator_next( &iter ) ) != end ) {
  *     _Chain_Iterator_set_position( &iter, node );
  *     _ISR_lock_Release_and_ISR_enable( &the_some->Lock, &lock_context );
  *     ( *visitor )( node );
  *     _ISR_lock_ISR_disable_and_acquire( &the_some->Lock, &lock_context );
  *   }
  *
  *   _Chain_Iterator_destroy( &iter );
  *   _ISR_lock_Release_and_ISR_enable( &the_some->Lock, &lock_context );
  * }
  * @endcode
  *
  * @param[out] the_chain The chain to iterate.
  * @param[in, out] the_registry The registry for the chain iterator.
  * @param[out] the_iterator The chain iterator to initialize.
  * @param[out] direction The iteration direction.
  *
  * @see _Chain_Iterator_next(), _Chain_Iterator_set_position() and
  * Chain_Iterator_destroy().
  *
  * @warning Think twice before you use a chain iterator.  Its current
  *   implementation is unfit for use in performance relevant components, due to
  *   the linear time complexity in _Chain_Iterator_registry_update().
  */
 static inline void _Chain_Iterator_initialize(
   Chain_Control            *the_chain,
   Chain_Iterator_registry  *the_registry,
   Chain_Iterator           *the_iterator,
   Chain_Iterator_direction  direction
 )
 {
   _Chain_Initialize_node( &the_iterator->Registry_node );
   _Chain_Append_unprotected(
     &the_registry->Iterators,
     &the_iterator->Registry_node
   );
 
   the_iterator->direction = direction;
 
   if ( direction == CHAIN_ITERATOR_FORWARD ) {
     the_iterator->position = _Chain_Head( the_chain );
   } else {
     the_iterator->position = _Chain_Tail( the_chain );
   }
 }
 
 /**
  * @brief Returns the next node in the iterator direction.
  *
  * In case a next node exists, then the iterator should be updated via
  * _Chain_Iterator_set_position() to continue with the next iteration step.
  *
  * @param[in, out] the_iterator The chain iterator.
  *
  * @return The next node in the iterator direction
  */
 static inline Chain_Node *_Chain_Iterator_next(
   const Chain_Iterator *the_iterator
 )
 {
   if ( the_iterator->direction == CHAIN_ITERATOR_FORWARD ) {
     return _Chain_Next( the_iterator->position );
   } else {
     return _Chain_Previous( the_iterator->position );
   }
 }
 
 /**
  * @brief Sets the iterator position.
  *
  * @param[out] the_iterator The chain iterator.
  * @param[out] the_node The new iterator position.
  */
 static inline void _Chain_Iterator_set_position(
   Chain_Iterator *the_iterator,
   Chain_Node     *the_node
 )
 {
   the_iterator->position = the_node;
 }
 
 /**
  * @brief Destroys the iterator.
  *
  * Removes the iterator from its registry.
  *
  * @param[out] the_iterator The chain iterator.
  */
 static inline void _Chain_Iterator_destroy(
   Chain_Iterator *the_iterator
 )
 {
   _Chain_Extract_unprotected( &the_iterator->Registry_node );
 }
 
 /** @} */
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif
 /* end of include file */

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