astobj2_rbtree.c

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/*
 * astobj2_hash - RBTree implementation for astobj2.
 *
 * Copyright (C) 2006 Marta Carbone, Luigi Rizzo - Univ. di Pisa, Italy
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief RBTree functions implementing astobj2 containers.
 *
 * \author Richard Mudgett <[email protected]>
 */

#include "asterisk.h"

#include "asterisk/_private.h"
#include "asterisk/astobj2.h"
#include "asterisk/utils.h"
#include "astobj2_private.h"
#include "astobj2_container_private.h"

/*!
 * A structure to hold the object held by the container and
 * where it is located in it.
 *
 * A red-black tree has the following properties:
 *
 * 1) Every node is either black or red.
 *
 * 2) The root is black.
 *
 * 3) If a node has a NULL child, that "child" is considered
 * black.
 *
 * 4) If a node is red, then both of its children are black.
 *
 * 5) Every path from a node to a descendant NULL child has the
 * same number of black nodes.  (Including the black NULL
 * child.)
 */
struct rbtree_node {
   /*!
    * \brief Items common to all container nodes.
    * \note Must be first in the specific node struct.
    */
   struct ao2_container_node common;
   /*! Parent node of this node. NULL if this is the root node. */
   struct rbtree_node *parent;
   /*! Left child node of this node.  NULL if does not have this child. */
   struct rbtree_node *left;
   /*! Right child node of this node.  NULL if does not have this child. */
   struct rbtree_node *right;
   /*! TRUE if the node is red. */
   unsigned int is_red:1;
};

/*!
 * A rbtree container in addition to values common to all
 * container types, stores the pointer to the root node of the
 * tree.
 */
struct ao2_container_rbtree {
   /*!
    * \brief Items common to all containers.
    * \note Must be first in the specific container struct.
    */
   struct ao2_container common;
   /*! Root node of the tree.  NULL if the tree is empty. */
   struct rbtree_node *root;
#if defined(AO2_DEBUG)
   struct {
      /*! Fixup insert left cases 1-3 */
      int fixup_insert_left[3];
      /*! Fixup insert right cases 1-3 */
      int fixup_insert_right[3];
      /*! Fixup delete left cases 1-4 */
      int fixup_delete_left[4];
      /*! Fixup delete right cases 1-4 */
      int fixup_delete_right[4];
      /*! Deletion of node with number of children (0-2). */
      int delete_children[3];
   } stats;
#endif   /* defined(AO2_DEBUG) */
};

enum equal_node_bias {
   /*! Bias search toward first matching node in the container. */
   BIAS_FIRST,
   /*! Bias search toward any matching node. */
   BIAS_EQUAL,
   /*! Bias search toward last matching node in the container. */
   BIAS_LAST,
};

enum empty_node_direction {
   GO_LEFT,
   GO_RIGHT,
};

/*! Traversal state to restart a rbtree container traversal. */
struct rbtree_traversal_state {
   /*! Active sort function in the traversal if not NULL. */
   ao2_sort_fn *sort_fn;
   /*! Saved comparison callback arg pointer. */
   void *arg;
   /*! Saved search flags to control traversing the container. */
   enum search_flags flags;
};

struct rbtree_traversal_state_check {
   /*
    * If we have a division by zero compile error here then there
    * is not enough room for the state.  Increase AO2_TRAVERSAL_STATE_SIZE.
    */
   char check[1 / (AO2_TRAVERSAL_STATE_SIZE / sizeof(struct rbtree_traversal_state))];
};

/*!
 * \internal
 * \brief Get the most left node in the tree.
 * \since 12.0.0
 *
 * \param node Starting node to find the most left node.
 *
 * \return Left most node.  Never NULL.
 */
static struct rbtree_node *rb_node_most_left(struct rbtree_node *node)
{
   while (node->left) {
      node = node->left;
   }

   return node;
}

/*!
 * \internal
 * \brief Get the most right node in the tree.
 * \since 12.0.0
 *
 * \param node Starting node to find the most right node.
 *
 * \return Right most node.  Never NULL.
 */
static struct rbtree_node *rb_node_most_right(struct rbtree_node *node)
{
   while (node->right) {
      node = node->right;
   }

   return node;
}

/*!
 * \internal
 * \brief Get the next node in ascending sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the next node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_next(struct rbtree_node *node)
{
   if (node->right) {
      return rb_node_most_left(node->right);
   }

   /* Find the parent that the node is a left child of. */
   while (node->parent) {
      if (node->parent->left == node) {
         /* We are the left child.  The parent is the next node. */
         return node->parent;
      }
      node = node->parent;
   }
   return NULL;
}

/*!
 * \internal
 * \brief Get the next node in descending sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the previous node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_prev(struct rbtree_node *node)
{
   if (node->left) {
      return rb_node_most_right(node->left);
   }

   /* Find the parent that the node is a right child of. */
   while (node->parent) {
      if (node->parent->right == node) {
         /* We are the right child.  The parent is the previous node. */
         return node->parent;
      }
      node = node->parent;
   }
   return NULL;
}

/*!
 * \internal
 * \brief Get the next node in pre-order sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the next node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_pre(struct rbtree_node *node)
{
   /* Visit the children if the node has any. */
   if (node->left) {
      return node->left;
   }
   if (node->right) {
      return node->right;
   }

   /* Time to go back up. */
   for (;;) {
      if (!node->parent) {
         return NULL;
      }
      if (node->parent->left == node && node->parent->right) {
         /*
          * We came up the left child and there's a right child.  Visit
          * it.
          */
         return node->parent->right;
      }
      node = node->parent;
   }
}

/*!
 * \internal
 * \brief Get the next node in post-order sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the next node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_post(struct rbtree_node *node)
{
   /* This node's children have already been visited. */
   for (;;) {
      if (!node->parent) {
         return NULL;
      }
      if (node->parent->left == node) {
         /* We came up the left child. */
         node = node->parent;

         /*
          * Find the right child's left most childless node.
          */
         while (node->right) {
            node = rb_node_most_left(node->right);
         }

         /*
          * This node's left child has already been visited or it doesn't
          * have any children.
          */
         return node;
      }

      /*
       * We came up the right child.
       *
       * This node's children have already been visited.  Time to
       * visit the parent.
       */
      return node->parent;
   }
}

/*!
 * \internal
 * \brief Get the next non-empty node in ascending sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the next node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_next_full(struct rbtree_node *node)
{
   for (;;) {
      node = rb_node_next(node);
      if (!node || node->common.obj) {
         return node;
      }
   }
}

/*!
 * \internal
 * \brief Get the next non-empty node in descending sequence.
 * \since 12.0.0
 *
 * \param node Starting node to find the previous node.
 *
 * \retval node on success.
 * \retval NULL if no node.
 */
static struct rbtree_node *rb_node_prev_full(struct rbtree_node *node)
{
   for (;;) {
      node = rb_node_prev(node);
      if (!node || node->common.obj) {
         return node;
      }
   }
}

/*!
 * \internal
 * \brief Determine which way to go from an empty node.
 * \since 12.0.0
 *
 * \param empty Empty node to determine which side obj_right goes on.
 * \param sort_fn Sort comparison function for non-empty nodes.
 * \param obj_right pointer to the (user-defined part) of an object.
 * \param flags flags from ao2_callback()
 *   OBJ_SEARCH_OBJECT - if set, 'obj_right', is an object.
 *   OBJ_SEARCH_KEY - if set, 'obj_right', is a search key item that is not an object.
 *   OBJ_SEARCH_PARTIAL_KEY - if set, 'obj_right', is a partial search key item that is not an object.
 * \param bias How to bias search direction for duplicates
 *
 * \return enum empty_node_direction to proceed.
 */
static enum empty_node_direction rb_find_empty_direction(struct rbtree_node *empty, ao2_sort_fn *sort_fn, void *obj_right, enum search_flags flags, enum equal_node_bias bias)
{
   int cmp;
   struct rbtree_node *cur;
   struct rbtree_node *right_most;

   /* Try for a quick definite go left. */
   if (!empty->left) {
      /* The empty node has no left child. */
      return GO_RIGHT;
   }
   right_most = rb_node_most_right(empty->left);
   if (right_most->common.obj) {
      cmp = sort_fn(right_most->common.obj, obj_right, flags);
      if (cmp < 0) {
         return GO_RIGHT;
      }
      if (cmp == 0 && bias == BIAS_LAST) {
         return GO_RIGHT;
      }
      return GO_LEFT;
   }

   /* Try for a quick definite go right. */
   if (!empty->right) {
      /* The empty node has no right child. */
      return GO_LEFT;
   }
   cur = rb_node_most_left(empty->right);
   if (cur->common.obj) {
      cmp = sort_fn(cur->common.obj, obj_right, flags);
      if (cmp > 0) {
         return GO_LEFT;
      }
      if (cmp == 0 && bias == BIAS_FIRST) {
         return GO_LEFT;
      }
      return GO_RIGHT;
   }

   /*
    * Have to scan the previous nodes from the right_most node of
    * the left subtree for the first non-empty node to determine
    * direction.
    */
   cur = right_most;
   for (;;) {
      /* Find previous node. */
      if (cur->left) {
         cur = rb_node_most_right(cur->left);
      } else {
         /* Find the parent that the node is a right child of. */
         for (;;) {
            if (cur->parent == empty) {
               /* The left side of the empty node is all empty nodes. */
               return GO_RIGHT;
            }
            if (cur->parent->right == cur) {
               /* We are the right child.  The parent is the previous node. */
               cur = cur->parent;
               break;
            }
            cur = cur->parent;
         }
      }

      if (cur->common.obj) {
         cmp = sort_fn(cur->common.obj, obj_right, flags);
         if (cmp < 0) {
            return GO_RIGHT;
         }
         if (cmp == 0 && bias == BIAS_LAST) {
            return GO_RIGHT;
         }
         return GO_LEFT;
      }
   }
}

/*!
 * \internal
 * \brief Tree node rotation left.
 * \since 12.0.0
 *
 * \param self Container holding node.
 * \param node Node to perform a left rotation with.
 *
 *        p                         p
 *        |     Left rotation       |
 *        N        --->             Ch
 *       / \                       / \
 *      a  Ch                     N   c
 *        / \                    / \
 *       b   c                  a   b
 *
 * N = node
 * Ch = child
 * p = parent
 * a,b,c = other nodes that are unaffected by the rotation.
 *
 * \note It is assumed that the node's right child exists.
 *
 * \return Nothing
 */
static void rb_rotate_left(struct ao2_container_rbtree *self, struct rbtree_node *node)
{
   struct rbtree_node *child; /*!< Node's right child. */

   child = node->right;

   /* Link the node's parent to the child. */
   if (!node->parent) {
      /* Node is the root so we get a new root node. */
      self->root = child;
   } else if (node->parent->left == node) {
      /* Node is a left child. */
      node->parent->left = child;
   } else {
      /* Node is a right child. */
      node->parent->right = child;
   }
   child->parent = node->parent;

   /* Link node's right subtree to the child's left subtree. */
   node->right = child->left;
   if (node->right) {
      node->right->parent = node;
   }

   /* Link the node to the child's left. */
   node->parent = child;
   child->left = node;
}

/*!
 * \internal
 * \brief Tree node rotation right.
 * \since 12.0.0
 *
 * \param self Container holding node.
 * \param node Node to perform a right rotation with.
 *
 *        p                         p
 *        |     Right rotation      |
 *        Ch                        N
 *       / \       <---            / \
 *      a  N                      Ch  c
 *        / \                    / \
 *       b   c                  a   b
 *
 * N = node
 * Ch = child
 * p = parent
 * a,b,c = other nodes that are unaffected by the rotation.
 *
 * \note It is assumed that the node's left child exists.
 *
 * \return Nothing
 */
static void rb_rotate_right(struct ao2_container_rbtree *self, struct rbtree_node *node)
{
   struct rbtree_node *child; /*!< Node's left child. */

   child = node->left;

   /* Link the node's parent to the child. */
   if (!node->parent) {
      /* Node is the root so we get a new root node. */
      self->root = child;
   } else if (node->parent->right == node) {
      /* Node is a right child. */
      node->parent->right = child;
   } else {
      /* Node is a left child. */
      node->parent->left = child;
   }
   child->parent = node->parent;

   /* Link node's left subtree to the child's right subtree. */
   node->left = child->right;
   if (node->left) {
      node->left->parent = node;
   }

   /* Link the node to the child's right. */
   node->parent = child;
   child->right = node;
}

/*!
 * \internal
 * \brief Create an empty copy of this container. (Debug version)
 * \since 14.0.0
 *
 * \param self Container to operate upon.
 * \param tag used for debugging.
 * \param file Debug file name invoked from
 * \param line Debug line invoked from
 * \param func Debug function name invoked from
 *
 * \retval empty-clone-container on success.
 * \retval NULL on error.
 */
static struct ao2_container *rb_ao2_alloc_empty_clone(struct ao2_container_rbtree *self,
   const char *tag, const char *file, int line, const char *func)
{
   if (!__is_ao2_object(self, file, line, func)) {
      return NULL;
   }

   return __ao2_container_alloc_rbtree(ao2_options_get(self), self->common.options,
      self->common.sort_fn, self->common.cmp_fn, tag, file, line, func);
}

/*!
 * \internal
 * \brief Fixup the rbtree after deleting a node.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param child Child of the node just deleted from the container.
 *
 * \note The child must be a dummy black node if there really
 * was no child of the deleted node.  Otherwise, the caller must
 * pass in the parent node and which child was deleted.  In
 * addition, the fixup routine would be more complicated.
 *
 * \return Nothing
 */
static void rb_delete_fixup(struct ao2_container_rbtree *self, struct rbtree_node *child)
{
   struct rbtree_node *sibling;

   while (self->root != child && !child->is_red) {
      if (child->parent->left == child) {
         /* Child is a left child. */
         sibling = child->parent->right;
         ast_assert(sibling != NULL);
         if (sibling->is_red) {
            /* Case 1: The child's sibling is red. */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_left[0]);
            sibling->is_red = 0;
            child->parent->is_red = 1;
            rb_rotate_left(self, child->parent);
            sibling = child->parent->right;
            ast_assert(sibling != NULL);
         }
         /*
          * The sibling is black.  A black node must have two children,
          * or one red child, or no children.
          */
         if ((!sibling->left || !sibling->left->is_red)
            && (!sibling->right || !sibling->right->is_red)) {
            /*
             * Case 2: The sibling is black and both of its children are black.
             *
             * This case handles the two black children or no children
             * possibilities of a black node.
             */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_left[1]);
            sibling->is_red = 1;
            child = child->parent;
         } else {
            /* At this point the sibling has at least one red child. */
            if (!sibling->right || !sibling->right->is_red) {
               /*
                * Case 3: The sibling is black, its left child is red, and its
                * right child is black.
                */
               AO2_DEVMODE_STAT(++self->stats.fixup_delete_left[2]);
               ast_assert(sibling->left != NULL);
               ast_assert(sibling->left->is_red);
               sibling->left->is_red = 0;
               sibling->is_red = 1;
               rb_rotate_right(self, sibling);
               sibling = child->parent->right;
               ast_assert(sibling != NULL);
            }
            /* Case 4: The sibling is black and its right child is red. */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_left[3]);
            sibling->is_red = child->parent->is_red;
            child->parent->is_red = 0;
            if (sibling->right) {
               sibling->right->is_red = 0;
            }
            rb_rotate_left(self, child->parent);
            child = self->root;
         }
      } else {
         /* Child is a right child. */
         sibling = child->parent->left;
         ast_assert(sibling != NULL);
         if (sibling->is_red) {
            /* Case 1: The child's sibling is red. */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_right[0]);
            sibling->is_red = 0;
            child->parent->is_red = 1;
            rb_rotate_right(self, child->parent);
            sibling = child->parent->left;
            ast_assert(sibling != NULL);
         }
         /*
          * The sibling is black.  A black node must have two children,
          * or one red child, or no children.
          */
         if ((!sibling->right || !sibling->right->is_red)
            && (!sibling->left || !sibling->left->is_red)) {
            /*
             * Case 2: The sibling is black and both of its children are black.
             *
             * This case handles the two black children or no children
             * possibilities of a black node.
             */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_right[1]);
            sibling->is_red = 1;
            child = child->parent;
         } else {
            /* At this point the sibling has at least one red child. */
            if (!sibling->left || !sibling->left->is_red) {
               /*
                * Case 3: The sibling is black, its right child is red, and its
                * left child is black.
                */
               AO2_DEVMODE_STAT(++self->stats.fixup_delete_right[2]);
               ast_assert(sibling->right != NULL);
               ast_assert(sibling->right->is_red);
               sibling->right->is_red = 0;
               sibling->is_red = 1;
               rb_rotate_left(self, sibling);
               sibling = child->parent->left;
               ast_assert(sibling != NULL);
            }
            /* Case 4: The sibling is black and its left child is red. */
            AO2_DEVMODE_STAT(++self->stats.fixup_delete_right[3]);
            sibling->is_red = child->parent->is_red;
            child->parent->is_red = 0;
            if (sibling->left) {
               sibling->left->is_red = 0;
            }
            rb_rotate_right(self, child->parent);
            child = self->root;
         }
      }
   }

   /*
    * Case 2 could leave the child node red and it needs to leave
    * with it black.
    *
    * Case 4 sets the child node to the root which of course must
    * be black.
    */
   child->is_red = 0;
}

/*!
 * \internal
 * \brief Delete the doomed node from this container.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param doomed Container node to delete from the container.
 *
 * \return Nothing
 */
static void rb_delete_node(struct ao2_container_rbtree *self, struct rbtree_node *doomed)
{
   struct rbtree_node *child;
   int need_fixup;

   if (doomed->left && doomed->right) {
      struct rbtree_node *next;
      int is_red;

      /*
       * The doomed node has two children.
       *
       * Find the next child node and swap it with the doomed node in
       * the tree.
       */
      AO2_DEVMODE_STAT(++self->stats.delete_children[2]);
      next = rb_node_most_left(doomed->right);
      SWAP(doomed->parent, next->parent);
      SWAP(doomed->left, next->left);
      SWAP(doomed->right, next->right);
      is_red = doomed->is_red;
      doomed->is_red = next->is_red;
      next->is_red = is_red;

      /* Link back in the next node. */
      if (!next->parent) {
         /* Doomed was the root so we get a new root node. */
         self->root = next;
      } else if (next->parent->left == doomed) {
         /* Doomed was the left child. */
         next->parent->left = next;
      } else {
         /* Doomed was the right child. */
         next->parent->right = next;
      }
      next->left->parent = next;
      if (next->right == next) {
         /* The next node was the right child of doomed. */
         next->right = doomed;
         doomed->parent = next;
      } else {
         next->right->parent = next;
         doomed->parent->left = doomed;
      }

      /* The doomed node has no left child now. */
      ast_assert(doomed->left == NULL);

      /*
       * We don't have to link the right child back in with doomed
       * since we are going to link it with doomed's parent anyway.
       */
      child = doomed->right;
   } else {
      /* Doomed has at most one child. */
      child = doomed->left;
      if (!child) {
         child = doomed->right;
      }
   }
   if (child) {
      AO2_DEVMODE_STAT(++self->stats.delete_children[1]);
   } else {
      AO2_DEVMODE_STAT(++self->stats.delete_children[0]);
   }

   need_fixup = (!doomed->is_red && !self->common.destroying);
   if (need_fixup && !child) {
      /*
       * Use the doomed node as a place holder node for the
       * nonexistent child so we also don't have to pass to the fixup
       * routine the parent and which child the deleted node came
       * from.
       */
      rb_delete_fixup(self, doomed);
      ast_assert(doomed->left == NULL);
      ast_assert(doomed->right == NULL);
      ast_assert(!doomed->is_red);
   }

   /* Link the child in place of doomed. */
   if (!doomed->parent) {
      /* Doomed was the root so we get a new root node. */
      self->root = child;
   } else if (doomed->parent->left == doomed) {
      /* Doomed was the left child. */
      doomed->parent->left = child;
   } else {
      /* Doomed was the right child. */
      doomed->parent->right = child;
   }
   if (child) {
      child->parent = doomed->parent;
      if (need_fixup) {
         rb_delete_fixup(self, child);
      }
   }

   AO2_DEVMODE_STAT(--self->common.nodes);
}

/*!
 * \internal
 * \brief Destroy a rbtree container node.
 * \since 12.0.0
 *
 * \param v_doomed Container node to destroy.
 *
 * \details
 * The container node unlinks itself from the container as part
 * of its destruction.  The node must be destroyed while the
 * container is already locked.
 *
 * \note The container must be locked when the node is
 * unreferenced.
 *
 * \return Nothing
 */
static void rb_ao2_node_destructor(void *v_doomed)
{
   struct rbtree_node *doomed = v_doomed;

   if (doomed->common.is_linked) {
      struct ao2_container_rbtree *my_container;

      /*
       * Promote to write lock if not already there.  Since
       * adjust_lock() can potentially release and block waiting for a
       * write lock, care must be taken to ensure that node references
       * are released before releasing the container references.
       *
       * Node references held by an iterator can only be held while
       * the iterator also holds a reference to the container.  These
       * node references must be unreferenced before the container can
       * be unreferenced to ensure that the node will not get a
       * negative reference and the destructor called twice for the
       * same node.
       */
      my_container = (struct ao2_container_rbtree *) doomed->common.my_container;
#ifdef AST_DEVMODE
      is_ao2_object(my_container);
#endif

      __adjust_lock(my_container, AO2_LOCK_REQ_WRLOCK, 1);

#if defined(AO2_DEBUG)
      if (!my_container->common.destroying
         && ao2_container_check(doomed->common.my_container, OBJ_NOLOCK)) {
         ast_log(LOG_ERROR, "Container integrity failed before node deletion.\n");
      }
#endif   /* defined(AO2_DEBUG) */
      rb_delete_node(my_container, doomed);
#if defined(AO2_DEBUG)
      if (!my_container->common.destroying
         && ao2_container_check(doomed->common.my_container, OBJ_NOLOCK)) {
         ast_log(LOG_ERROR, "Container integrity failed after node deletion.\n");
      }
#endif   /* defined(AO2_DEBUG) */
   }

   /*
    * We could have an object in the node if the container is being
    * destroyed or the node had not been linked in yet.
    */
   if (doomed->common.obj) {
      __container_unlink_node(&doomed->common, AO2_UNLINK_NODE_UNLINK_OBJECT);
   }
}

/*!
 * \internal
 * \brief Create a new container node.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param obj_new Object to put into the node.
 * \param tag used for debugging.
 * \param file Debug file name invoked from
 * \param line Debug line invoked from
 * \param func Debug function name invoked from
 *
 * \retval initialized-node on success.
 * \retval NULL on error.
 */
static struct rbtree_node *rb_ao2_new_node(struct ao2_container_rbtree *self, void *obj_new, const char *tag, const char *file, int line, const char *func)
{
   struct rbtree_node *node;

   node = ao2_alloc_options(sizeof(*node), rb_ao2_node_destructor,
      AO2_ALLOC_OPT_LOCK_NOLOCK | AO2_ALLOC_OPT_NO_REF_DEBUG);
   if (!node) {
      return NULL;
   }

   __ao2_ref(obj_new, +1, tag ?: "Container node creation", file, line, func);
   node->common.obj = obj_new;
   node->common.my_container = (struct ao2_container *) self;

   return node;
}

/*!
 * \internal
 * \brief Fixup the rbtree after inserting a node.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param node Container node just inserted into the container.
 *
 * \note The just inserted node is red.
 *
 * \return Nothing
 */
static void rb_insert_fixup(struct ao2_container_rbtree *self, struct rbtree_node *node)
{
   struct rbtree_node *g_parent; /* Grand parent node. */

   while (node->parent && node->parent->is_red) {
      g_parent = node->parent->parent;

      /* The grand parent must exist if the parent is red. */
      ast_assert(g_parent != NULL);

      if (node->parent == g_parent->left) {
         /* The parent is a left child. */
         if (g_parent->right && g_parent->right->is_red) {
            /* Case 1: Push the black down from the grand parent node. */
            AO2_DEVMODE_STAT(++self->stats.fixup_insert_left[0]);
            g_parent->right->is_red = 0;
            g_parent->left->is_red = 0;
            g_parent->is_red = 1;

            node = g_parent;
         } else {
            /* The uncle node is black. */
            if (node->parent->right == node) {
               /*
                * Case 2: The node is a right child.
                *
                * Which node is the grand parent does not change.
                */
               AO2_DEVMODE_STAT(++self->stats.fixup_insert_left[1]);
               node = node->parent;
               rb_rotate_left(self, node);
            }
            /* Case 3: The node is a left child. */
            AO2_DEVMODE_STAT(++self->stats.fixup_insert_left[2]);
            node->parent->is_red = 0;
            g_parent->is_red = 1;
            rb_rotate_right(self, g_parent);
         }
      } else {
         /* The parent is a right child. */
         if (g_parent->left && g_parent->left->is_red) {
            /* Case 1: Push the black down from the grand parent node. */
            AO2_DEVMODE_STAT(++self->stats.fixup_insert_right[0]);
            g_parent->left->is_red = 0;
            g_parent->right->is_red = 0;
            g_parent->is_red = 1;

            node = g_parent;
         } else {
            /* The uncle node is black. */
            if (node->parent->left == node) {
               /*
                * Case 2: The node is a left child.
                *
                * Which node is the grand parent does not change.
                */
               AO2_DEVMODE_STAT(++self->stats.fixup_insert_right[1]);
               node = node->parent;
               rb_rotate_right(self, node);
            }
            /* Case 3: The node is a right child. */
            AO2_DEVMODE_STAT(++self->stats.fixup_insert_right[2]);
            node->parent->is_red = 0;
            g_parent->is_red = 1;
            rb_rotate_left(self, g_parent);
         }
      }
   }

   /*
    * The root could be red here because:
    * 1) We just inserted the root node in an empty tree.
    *
    * 2) Case 1 could leave the root red if the grand parent were
    * the root.
    */
   self->root->is_red = 0;
}

/*!
 * \internal
 * \brief Insert a node into this container.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param node Container node to insert into the container.
 *
 * \return enum ao2_container_insert value.
 */
static enum ao2_container_insert rb_ao2_insert_node(struct ao2_container_rbtree *self, struct rbtree_node *node)
{
   int cmp;
   struct rbtree_node *cur;
   struct rbtree_node *next;
   ao2_sort_fn *sort_fn;
   uint32_t options;
   enum equal_node_bias bias;

   if (!self->root) {
      /* The tree is empty. */
      self->root = node;
      return AO2_CONTAINER_INSERT_NODE_INSERTED;
   }

   sort_fn = self->common.sort_fn;
   options = self->common.options;
   switch (options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
   default:
   case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
      if (options & AO2_CONTAINER_ALLOC_OPT_INSERT_BEGIN) {
         bias = BIAS_FIRST;
      } else {
         bias = BIAS_LAST;
      }
      break;
   case AO2_CONTAINER_ALLOC_OPT_DUPS_REJECT:
   case AO2_CONTAINER_ALLOC_OPT_DUPS_OBJ_REJECT:
   case AO2_CONTAINER_ALLOC_OPT_DUPS_REPLACE:
      bias = BIAS_EQUAL;
      break;
   }

   /*
    * New nodes are always colored red when initially inserted into
    * the tree.  (Except for the root which is always black.)
    */
   node->is_red = 1;

   /* Find node where normal insert would put a new node. */
   cur = self->root;
   for (;;) {
      if (!cur->common.obj) {
         /* Which direction do we go to insert this node? */
         if (rb_find_empty_direction(cur, sort_fn, node->common.obj, OBJ_SEARCH_OBJECT, bias)
            == GO_LEFT) {
            if (cur->left) {
               cur = cur->left;
               continue;
            }

            /* Node becomes a left child */
            cur->left = node;
            node->parent = cur;
            rb_insert_fixup(self, node);
            return AO2_CONTAINER_INSERT_NODE_INSERTED;
         }
         if (cur->right) {
            cur = cur->right;
            continue;
         }

         /* Node becomes a right child */
         cur->right = node;
         node->parent = cur;
         rb_insert_fixup(self, node);
         return AO2_CONTAINER_INSERT_NODE_INSERTED;
      }
      cmp = sort_fn(cur->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
      if (cmp > 0) {
         if (cur->left) {
            cur = cur->left;
            continue;
         }

         /* Node becomes a left child */
         cur->left = node;
         node->parent = cur;
         rb_insert_fixup(self, node);
         return AO2_CONTAINER_INSERT_NODE_INSERTED;
      } else if (cmp < 0) {
         if (cur->right) {
            cur = cur->right;
            continue;
         }

         /* Node becomes a right child */
         cur->right = node;
         node->parent = cur;
         rb_insert_fixup(self, node);
         return AO2_CONTAINER_INSERT_NODE_INSERTED;
      }
      switch (bias) {
      case BIAS_FIRST:
         /* Duplicate nodes unconditionally accepted. */
         if (cur->left) {
            cur = cur->left;
            continue;
         }

         /* Node becomes a left child */
         cur->left = node;
         node->parent = cur;
         rb_insert_fixup(self, node);
         return AO2_CONTAINER_INSERT_NODE_INSERTED;
      case BIAS_EQUAL:
         break;
      case BIAS_LAST:
         /* Duplicate nodes unconditionally accepted. */
         if (cur->right) {
            cur = cur->right;
            continue;
         }

         /* Node becomes a right child */
         cur->right = node;
         node->parent = cur;
         rb_insert_fixup(self, node);
         return AO2_CONTAINER_INSERT_NODE_INSERTED;
      }

      break;
   }

   /* Node is a dupliate */
   switch (options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
   default:
   case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
      ast_assert(0);/* Case already handled by BIAS_FIRST/BIAS_LAST. */
      return AO2_CONTAINER_INSERT_NODE_REJECTED;
   case AO2_CONTAINER_ALLOC_OPT_DUPS_REJECT:
      /* Reject all objects with the same key. */
      return AO2_CONTAINER_INSERT_NODE_REJECTED;
   case AO2_CONTAINER_ALLOC_OPT_DUPS_OBJ_REJECT:
      if (cur->common.obj == node->common.obj) {
         /* Reject inserting the same object */
         return AO2_CONTAINER_INSERT_NODE_REJECTED;
      }
      next = cur;
      if (options & AO2_CONTAINER_ALLOC_OPT_INSERT_BEGIN) {
         /* Search to end of duplicates for the same object. */
         for (;;) {
            next = rb_node_next_full(next);
            if (!next) {
               break;
            }
            if (next->common.obj == node->common.obj) {
               /* Reject inserting the same object */
               return AO2_CONTAINER_INSERT_NODE_REJECTED;
            }
            cmp = sort_fn(next->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp) {
               break;
            }
         }

         /* Find first duplicate node. */
         for (;;) {
            next = rb_node_prev_full(cur);
            if (!next) {
               break;
            }
            if (next->common.obj == node->common.obj) {
               /* Reject inserting the same object */
               return AO2_CONTAINER_INSERT_NODE_REJECTED;
            }
            cmp = sort_fn(next->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp) {
               break;
            }
            cur = next;
         }
         if (!cur->left) {
            /* Node becomes a left child */
            cur->left = node;
         } else {
            /* Node becomes a right child */
            cur = rb_node_most_right(cur->left);
            cur->right = node;
         }
      } else {
         /* Search to beginning of duplicates for the same object. */
         for (;;) {
            next = rb_node_prev_full(next);
            if (!next) {
               break;
            }
            if (next->common.obj == node->common.obj) {
               /* Reject inserting the same object */
               return AO2_CONTAINER_INSERT_NODE_REJECTED;
            }
            cmp = sort_fn(next->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp) {
               break;
            }
         }

         /* Find last duplicate node. */
         for (;;) {
            next = rb_node_next_full(cur);
            if (!next) {
               break;
            }
            if (next->common.obj == node->common.obj) {
               /* Reject inserting the same object */
               return AO2_CONTAINER_INSERT_NODE_REJECTED;
            }
            cmp = sort_fn(next->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp) {
               break;
            }
            cur = next;
         }
         if (!cur->right) {
            /* Node becomes a right child */
            cur->right = node;
         } else {
            /* Node becomes a left child */
            cur = rb_node_most_left(cur->right);
            cur->left = node;
         }
      }
      break;
   case AO2_CONTAINER_ALLOC_OPT_DUPS_REPLACE:
      SWAP(cur->common.obj, node->common.obj);
      ao2_ref(node, -1);
      return AO2_CONTAINER_INSERT_NODE_OBJ_REPLACED;
   }

   /* Complete inserting duplicate node. */
   node->parent = cur;
   rb_insert_fixup(self, node);
   return AO2_CONTAINER_INSERT_NODE_INSERTED;
}

/*!
 * \internal
 * \brief Find the next rbtree container node in a traversal.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param state Traversal state to restart rbtree container traversal.
 * \param prev Previous node returned by the traversal search functions.
 *    The ref ownership is passed back to this function.
 *
 * \retval node-ptr of found node (Reffed).
 * \retval NULL when no node found.
 */
static struct rbtree_node *rb_ao2_find_next(struct ao2_container_rbtree *self, struct rbtree_traversal_state *state, struct rbtree_node *prev)
{
   struct rbtree_node *node;
   void *arg;
   enum search_flags flags;
   int cmp;

   arg = state->arg;
   flags = state->flags;

   node = prev;
   for (;;) {
      /* Find next node in traversal order. */
      switch (flags & OBJ_ORDER_MASK) {
      default:
      case OBJ_ORDER_ASCENDING:
         node = rb_node_next(node);
         break;
      case OBJ_ORDER_DESCENDING:
         node = rb_node_prev(node);
         break;
      case OBJ_ORDER_PRE:
         node = rb_node_pre(node);
         break;
      case OBJ_ORDER_POST:
         node = rb_node_post(node);
         break;
      }
      if (!node) {
         /* No more nodes left to traverse. */
         break;
      }
      if (!node->common.obj) {
         /* Node is empty */
         continue;
      }

      if (state->sort_fn) {
         /* Filter node through the sort_fn */
         cmp = state->sort_fn(node->common.obj, arg, flags & OBJ_SEARCH_MASK);
         if (cmp) {
            /* No more nodes in this container are possible to match. */
            break;
         }
      }

      /* We have the next traversal node */
      ao2_ref(node, +1);

      /*
       * Dereferencing the prev node may result in our next node
       * object being removed by another thread.  This could happen if
       * the container uses RW locks and the container was read
       * locked.
       */
      ao2_ref(prev, -1);
      if (node->common.obj) {
         return node;
      }
      prev = node;
   }

   /* No more nodes in the container left to traverse. */
   ao2_ref(prev, -1);
   return NULL;
}

/*!
 * \internal
 * \brief Find an initial matching node.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param obj_right pointer to the (user-defined part) of an object.
 * \param flags flags from ao2_callback()
 *   OBJ_SEARCH_OBJECT - if set, 'obj_right', is an object.
 *   OBJ_SEARCH_KEY - if set, 'obj_right', is a search key item that is not an object.
 *   OBJ_SEARCH_PARTIAL_KEY - if set, 'obj_right', is a partial search key item that is not an object.
 * \param bias How to bias search direction for duplicates
 *
 * \retval node on success.
 * \retval NULL if not found.
 */
static struct rbtree_node *rb_find_initial(struct ao2_container_rbtree *self, void *obj_right, enum search_flags flags, enum equal_node_bias bias)
{
   int cmp;
   enum search_flags sort_flags;
   struct rbtree_node *node;
   struct rbtree_node *next = NULL;
   ao2_sort_fn *sort_fn;

   sort_flags = flags & OBJ_SEARCH_MASK;
   sort_fn = self->common.sort_fn;

   /* Find node where normal search would find it. */
   node = self->root;
   if (!node) {
      return NULL;
   }
   for (;;) {
      if (!node->common.obj) {
         /* Which direction do we go to find the node? */
         if (rb_find_empty_direction(node, sort_fn, obj_right, sort_flags, bias)
            == GO_LEFT) {
            next = node->left;
         } else {
            next = node->right;
         }
         if (!next) {
            switch (bias) {
            case BIAS_FIRST:
               /* Check successor node for match. */
               next = rb_node_next_full(node);
               break;
            case BIAS_EQUAL:
               break;
            case BIAS_LAST:
               /* Check previous node for match. */
               next = rb_node_prev_full(node);
               break;
            }
            if (next) {
               cmp = sort_fn(next->common.obj, obj_right, sort_flags);
               if (cmp == 0) {
                  /* Found the first/last matching node. */
                  return next;
               }
               next = NULL;
            }

            /* No match found. */
            return next;
         }
      } else {
         cmp = sort_fn(node->common.obj, obj_right, sort_flags);
         if (cmp > 0) {
            next = node->left;
         } else if (cmp < 0) {
            next = node->right;
         } else {
            switch (bias) {
            case BIAS_FIRST:
               next = node->left;
               break;
            case BIAS_EQUAL:
               return node;
            case BIAS_LAST:
               next = node->right;
               break;
            }
            if (!next) {
               /* Found the first/last matching node. */
               return node;
            }
         }
         if (!next) {
            switch (bias) {
            case BIAS_FIRST:
               if (cmp < 0) {
                  /* Check successor node for match. */
                  next = rb_node_next_full(node);
               }
               break;
            case BIAS_EQUAL:
               break;
            case BIAS_LAST:
               if (cmp > 0) {
                  /* Check previous node for match. */
                  next = rb_node_prev_full(node);
               }
               break;
            }
            if (next) {
               cmp = sort_fn(next->common.obj, obj_right, sort_flags);
               if (cmp == 0) {
                  /* Found the first/last matching node. */
                  return next;
               }
            }

            /* No match found. */
            return NULL;
         }
      }
      node = next;
   }
}

/*!
 * \internal
 * \brief Find the first rbtree container node in a traversal.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param flags search_flags to control traversing the container
 * \param arg Comparison callback arg parameter.
 * \param state Traversal state to restart rbtree container traversal.
 *
 * \retval node-ptr of found node (Reffed).
 * \retval NULL when no node found.
 */
static struct rbtree_node *rb_ao2_find_first(struct ao2_container_rbtree *self, enum search_flags flags, void *arg, struct rbtree_traversal_state *state)
{
   struct rbtree_node *node;
   enum equal_node_bias bias;

   if (self->common.destroying) {
      /* Force traversal to be post order for tree destruction. */
      flags = OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE | OBJ_ORDER_POST;
   }

   memset(state, 0, sizeof(*state));
   state->arg = arg;
   state->flags = flags;

   switch (flags & OBJ_SEARCH_MASK) {
   case OBJ_SEARCH_OBJECT:
   case OBJ_SEARCH_KEY:
   case OBJ_SEARCH_PARTIAL_KEY:
      /* We are asked to do a directed search. */
      state->sort_fn = self->common.sort_fn;
      break;
   default:
      /* Don't know, let's visit all nodes */
      state->sort_fn = NULL;
      break;
   }

   if (!self->root) {
      /* Tree is empty. */
      return NULL;
   }

   /* Find first traversal node. */
   switch (flags & OBJ_ORDER_MASK) {
   default:
   case OBJ_ORDER_ASCENDING:
      if (!state->sort_fn) {
         /* Find left most child. */
         node = rb_node_most_left(self->root);
         if (!node->common.obj) {
            node = rb_node_next_full(node);
            if (!node) {
               return NULL;
            }
         }
         break;
      }

      /* Search for initial node. */
      switch (self->common.options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
      case AO2_CONTAINER_ALLOC_OPT_DUPS_REJECT:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_REPLACE:
         if ((flags & OBJ_SEARCH_MASK) != OBJ_SEARCH_PARTIAL_KEY) {
            /* There are no duplicates allowed. */
            bias = BIAS_EQUAL;
            break;
         }
         /* Fall through */
      default:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_OBJ_REJECT:
         /* Find first duplicate node. */
         bias = BIAS_FIRST;
         break;
      }
      node = rb_find_initial(self, arg, flags, bias);
      if (!node) {
         return NULL;
      }
      break;
   case OBJ_ORDER_DESCENDING:
      if (!state->sort_fn) {
         /* Find right most child. */
         node = rb_node_most_right(self->root);
         if (!node->common.obj) {
            node = rb_node_prev_full(node);
            if (!node) {
               return NULL;
            }
         }
         break;
      }

      /* Search for initial node. */
      switch (self->common.options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
      case AO2_CONTAINER_ALLOC_OPT_DUPS_REJECT:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_REPLACE:
         if ((flags & OBJ_SEARCH_MASK) != OBJ_SEARCH_PARTIAL_KEY) {
            /* There are no duplicates allowed. */
            bias = BIAS_EQUAL;
            break;
         }
         /* Fall through */
      default:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
      case AO2_CONTAINER_ALLOC_OPT_DUPS_OBJ_REJECT:
         /* Find last duplicate node. */
         bias = BIAS_LAST;
         break;
      }
      node = rb_find_initial(self, arg, flags, bias);
      if (!node) {
         return NULL;
      }
      break;
   case OBJ_ORDER_PRE:
      /* This is a tree structure traversal so we must visit all nodes. */
      state->sort_fn = NULL;

      node = self->root;

      /* Find a non-empty node. */
      while (!node->common.obj) {
         node = rb_node_pre(node);
         if (!node) {
            return NULL;
         }
      }
      break;
   case OBJ_ORDER_POST:
      /* This is a tree structure traversal so we must visit all nodes. */
      state->sort_fn = NULL;

      /* Find the left most childless node. */
      node = self->root;
      for (;;) {
         node = rb_node_most_left(node);
         if (!node->right) {
            /* This node has no children. */
            break;
         }
         node = node->right;
      }

      /* Find a non-empty node. */
      while (!node->common.obj) {
         node = rb_node_post(node);
         if (!node) {
            return NULL;
         }
      }
      break;
   }

   /* We have the first traversal node */
   ao2_ref(node, +1);
   return node;
}

/*!
 * \internal
 * \brief Find the next non-empty iteration node in the container.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param node Previous node returned by the iterator.
 * \param flags search_flags to control iterating the container.
 *   Only AO2_ITERATOR_DESCENDING is useful by the method.
 *
 * \note The container is already locked.
 *
 * \retval node on success.
 * \retval NULL on error or no more nodes in the container.
 */
static struct rbtree_node *rb_ao2_iterator_next(struct ao2_container_rbtree *self, struct rbtree_node *node, enum ao2_iterator_flags flags)
{
   if (flags & AO2_ITERATOR_DESCENDING) {
      if (!node) {
         /* Find right most node. */
         if (!self->root) {
            return NULL;
         }
         node = rb_node_most_right(self->root);
         if (node->common.obj) {
            /* Found a non-empty node. */
            return node;
         }
      }
      /* Find next non-empty node. */
      node = rb_node_prev_full(node);
   } else {
      if (!node) {
         /* Find left most node. */
         if (!self->root) {
            return NULL;
         }
         node = rb_node_most_left(self->root);
         if (node->common.obj) {
            /* Found a non-empty node. */
            return node;
         }
      }
      /* Find next non-empty node. */
      node = rb_node_next_full(node);
   }

   return node;
}

/*!
 * \internal
 *
 * \brief Destroy this container.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 *
 * \return Nothing
 */
static void rb_ao2_destroy(struct ao2_container_rbtree *self)
{
   /* Check that the container no longer has any nodes */
   if (self->root) {
      ast_log(LOG_ERROR, "Node ref leak.  Red-Black tree container still has nodes!\n");
      ast_assert(0);
   }
}

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Display contents of the specified container.
 * \since 12.0.0
 *
 * \param self Container to dump.
 * \param where User data needed by prnt to determine where to put output.
 * \param prnt Print output callback function to use.
 * \param prnt_obj Callback function to print the given object's key. (NULL if not available)
 *
 * \return Nothing
 */
static void rb_ao2_dump(struct ao2_container_rbtree *self, void *where, ao2_prnt_fn *prnt, ao2_prnt_obj_fn *prnt_obj)
{
#define FORMAT  "%16s, %16s, %16s, %16s, %5s, %16s, %s\n"
#define FORMAT2 "%16p, %16p, %16p, %16p, %5s, %16p, "

   struct rbtree_node *node;

   prnt(where, FORMAT, "Node", "Parent", "Left", "Right", "Color", "Obj", "Key");
   for (node = self->root; node; node = rb_node_pre(node)) {
      prnt(where, FORMAT2,
         node,
         node->parent,
         node->left,
         node->right,
         node->is_red ? "Red" : "Black",
         node->common.obj);
      if (node->common.obj && prnt_obj) {
         prnt_obj(node->common.obj, where, prnt);
      }
      prnt(where, "\n");
   }

#undef FORMAT
#undef FORMAT2
}
#endif   /* defined(AO2_DEBUG) */

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Display statistics of the specified container.
 * \since 12.0.0
 *
 * \param self Container to display statistics.
 * \param where User data needed by prnt to determine where to put output.
 * \param prnt Print output callback function to use.
 *
 * \note The container is already locked for reading.
 *
 * \return Nothing
 */
static void rb_ao2_stats(struct ao2_container_rbtree *self, void *where, ao2_prnt_fn *prnt)
{
   int idx;

   for (idx = 0; idx < ARRAY_LEN(self->stats.fixup_insert_left); ++idx) {
      prnt(where, "Number of left insert fixups case %d: %d\n", idx + 1,
         self->stats.fixup_insert_left[idx]);
   }
   for (idx = 0; idx < ARRAY_LEN(self->stats.fixup_insert_right); ++idx) {
      prnt(where, "Number of right insert fixups case %d: %d\n", idx + 1,
         self->stats.fixup_insert_right[idx]);
   }

   for (idx = 0; idx < ARRAY_LEN(self->stats.delete_children); ++idx) {
      prnt(where, "Number of nodes deleted with %d children: %d\n", idx,
         self->stats.delete_children[idx]);
   }
   for (idx = 0; idx < ARRAY_LEN(self->stats.fixup_delete_left); ++idx) {
      prnt(where, "Number of left delete fixups case %d: %d\n", idx + 1,
         self->stats.fixup_delete_left[idx]);
   }
   for (idx = 0; idx < ARRAY_LEN(self->stats.fixup_delete_right); ++idx) {
      prnt(where, "Number of right delete fixups case %d: %d\n", idx + 1,
         self->stats.fixup_delete_right[idx]);
   }
}
#endif   /* defined(AO2_DEBUG) */

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Check the black height of the given node.
 * \since 12.0.0
 *
 * \param node Node to check black height.
 *
 * \retval black-height of node on success.
 * \retval -1 on error.  Node black height did not balance.
 */
static int rb_check_black_height(struct rbtree_node *node)
{
   int height_left;
   int height_right;

   if (!node) {
      /* A NULL child is a black node. */
      return 0;
   }

   height_left = rb_check_black_height(node->left);
   if (height_left < 0) {
      return -1;
   }
   height_right = rb_check_black_height(node->right);
   if (height_right < 0) {
      return -1;
   }
   if (height_left != height_right) {
      ast_log(LOG_ERROR,
         "Tree node black height of children does not match! L:%d != R:%d\n",
         height_left, height_right);
      return -1;
   }
   if (!node->is_red) {
      /* The node itself is black. */
      ++height_left;
   }
   return height_left;
}

#endif   /* defined(AO2_DEBUG) */

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Perform an integrity check on the specified container.
 * \since 12.0.0
 *
 * \param self Container to check integrity.
 *
 * \note The container is already locked for reading.
 *
 * \retval 0 on success.
 * \retval -1 on error.
 */
static int rb_ao2_integrity(struct ao2_container_rbtree *self)
{
   int res;
   int count_node;
   int count_obj;
   void *obj_last;
   struct rbtree_node *node;

   res = 0;

   count_node = 0;
   count_obj = 0;

   /*
    * See the properties listed at struct rbtree_node definition.
    *
    * The rbtree properties 1 and 3 are not testable.
    *
    * Property 1 is not testable because we are not rebalancing at
    * this time so all nodes are either red or black.
    *
    * Property 3 is not testable because it is the definition of a
    * NULL child.
    */
   if (self->root) {
      /* Check tree links. */
      if (self->root->parent) {
         if (self->root->parent == self->root) {
            ast_log(LOG_ERROR, "Tree root parent pointer points to itself!\n");
         } else {
            ast_log(LOG_ERROR, "Tree root is not a root node!\n");
         }
         return -1;
      }
      if (self->root->is_red) {
         /* Violation rbtree property 2. */
         ast_log(LOG_ERROR, "Tree root is red!\n");
         res = -1;
      }
      node = self->root;
      do {
         if (node->left) {
            if (node->left == node) {
               ast_log(LOG_ERROR, "Tree node's left pointer points to itself!\n");
               return -1;
            }
            if (node->left->parent != node) {
               ast_log(LOG_ERROR, "Tree node's left child does not link back!\n");
               return -1;
            }
         }
         if (node->right) {
            if (node->right == node) {
               ast_log(LOG_ERROR, "Tree node's right pointer points to itself!\n");
               return -1;
            }
            if (node->right->parent != node) {
               ast_log(LOG_ERROR, "Tree node's right child does not link back!\n");
               return -1;
            }
         }

         /* Check red/black node flags. */
         if (node->is_red) {
            /* A red node must have two black children or no children. */
            if (node->left && node->right) {
               /* Node has two children. */
               if (node->left->is_red) {
                  /* Violation rbtree property 4. */
                  ast_log(LOG_ERROR, "Tree node is red and its left child is red!\n");
                  res = -1;
               }
               if (node->right->is_red) {
                  /* Violation rbtree property 4. */
                  ast_log(LOG_ERROR, "Tree node is red and its right child is red!\n");
                  res = -1;
               }
            } else if (node->left || node->right) {
               /*
                * Violation rbtree property 4 if the child is red.
                * Violation rbtree property 5 if the child is black.
                */
               ast_log(LOG_ERROR, "Tree node is red and it only has one child!\n");
               res = -1;
            }
         } else {
            /*
             * A black node must have two children, or one red child, or no
             * children.  If the black node has two children and only one of
             * them is red, that red child must have two children.
             */
            if (node->left && node->right) {
               /* Node has two children. */
               if (node->left->is_red != node->right->is_red) {
                  /* The children are not the same color. */
                  struct rbtree_node *red;

                  if (node->left->is_red) {
                     red = node->left;
                  } else {
                     red = node->right;
                  }
                  if (!red->left || !red->right) {
                     /* Violation rbtree property 5. */
                     ast_log(LOG_ERROR,
                        "Tree node is black and the red child does not have two children!\n");
                     res = -1;
                  }
               }
            } else if ((node->left && !node->left->is_red)
               || (node->right && !node->right->is_red)) {
               /* Violation rbtree property 5. */
               ast_log(LOG_ERROR, "Tree node is black and its only child is black!\n");
               res = -1;
            }
         }

         /* Count nodes and objects. */
         ++count_node;
         if (node->common.obj) {
            ++count_obj;
         }

         node = rb_node_pre(node);
      } while (node);

      /* Check node key sort order. */
      obj_last = NULL;
      for (node = rb_node_most_left(self->root); node; node = rb_node_next(node)) {
         if (!node->common.obj) {
            /* Node is empty. */
            continue;
         }

         if (obj_last) {
            if (self->common.sort_fn(obj_last, node->common.obj, OBJ_SEARCH_OBJECT) > 0) {
               ast_log(LOG_ERROR, "Tree nodes are out of sorted order!\n");
               return -1;
            }
         }
         obj_last = node->common.obj;
      }

      /* Completely check property 5 */
      if (!res && rb_check_black_height(self->root) < 0) {
         /* Violation rbtree property 5. */
         res = -1;
      }
   }

   /* Check total obj count. */
   if (count_obj != ao2_container_count(&self->common)) {
      ast_log(LOG_ERROR, "Total object count does not match ao2_container_count()!\n");
      return -1;
   }

   /* Check total node count. */
   if (count_node != self->common.nodes) {
      ast_log(LOG_ERROR, "Total node count of %d does not match stat of %d!\n",
         count_node, self->common.nodes);
      return -1;
   }

   return res;
}
#endif   /* defined(AO2_DEBUG) */

/*! rbtree container virtual method table. */
static const struct ao2_container_methods v_table_rbtree = {
   .alloc_empty_clone = (ao2_container_alloc_empty_clone_fn) rb_ao2_alloc_empty_clone,
   .new_node = (ao2_container_new_node_fn) rb_ao2_new_node,
   .insert = (ao2_container_insert_fn) rb_ao2_insert_node,
   .traverse_first = (ao2_container_find_first_fn) rb_ao2_find_first,
   .traverse_next = (ao2_container_find_next_fn) rb_ao2_find_next,
   .iterator_next = (ao2_iterator_next_fn) rb_ao2_iterator_next,
   .destroy = (ao2_container_destroy_fn) rb_ao2_destroy,
#if defined(AO2_DEBUG)
   .dump = (ao2_container_display) rb_ao2_dump,
   .stats = (ao2_container_statistics) rb_ao2_stats,
   .integrity = (ao2_container_integrity) rb_ao2_integrity,
#endif   /* defined(AO2_DEBUG) */
};

/*!
 * \brief Initialize a rbtree container.
 *
 * \param self Container to initialize.
 * \param options Container behaviour options (See enum ao2_container_opts)
 * \param sort_fn Pointer to a sort function.
 * \param cmp_fn Pointer to a compare function used by ao2_find.
 *
 * \return A pointer to a struct container.
 */
static struct ao2_container *rb_ao2_container_init(struct ao2_container_rbtree *self,
   unsigned int options, ao2_sort_fn *sort_fn, ao2_callback_fn *cmp_fn)
{
   if (!self) {
      return NULL;
   }

   self->common.v_table = &v_table_rbtree;
   self->common.sort_fn = sort_fn;
   self->common.cmp_fn = cmp_fn;
   self->common.options = options;

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_containers, 1);
#endif   /* defined(AO2_DEBUG) */

   return (struct ao2_container *) self;
}

struct ao2_container *__ao2_container_alloc_rbtree(unsigned int ao2_options, unsigned int container_options,
   ao2_sort_fn *sort_fn, ao2_callback_fn *cmp_fn,
   const char *tag, const char *file, int line, const char *func)
{
   struct ao2_container_rbtree *self;

   if (!sort_fn) {
      /* Sanity checks. */
      ast_log(__LOG_ERROR, file, line, func, "Missing sort_fn()!\n");
      return NULL;
   }

   self = __ao2_alloc(sizeof(*self), container_destruct, ao2_options,
      tag ?: __PRETTY_FUNCTION__, file, line, func);
   return rb_ao2_container_init(self, container_options, sort_fn, cmp_fn);
}