astobj2_hash.c

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/*
 * astobj2_hash - Hash table 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 Hash table functions implementing astobj2 containers.
 *
 * \author Richard Mudgett <[email protected]>
 */

#include "asterisk.h"

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

/*!
 * A structure to create a linked list of entries,
 * used within a bucket.
 */
struct hash_bucket_node {
   /*!
    * \brief Items common to all container nodes.
    * \note Must be first in the specific node struct.
    */
   struct ao2_container_node common;
   /*! Next node links in the list. */
   AST_DLLIST_ENTRY(hash_bucket_node) links;
   /*! Hash bucket holding the node. */
   int my_bucket;
};

struct hash_bucket {
   /*! List of objects held in the bucket. */
   AST_DLLIST_HEAD_NOLOCK(, hash_bucket_node) list;
#if defined(AO2_DEBUG)
   /*! Number of elements currently in the bucket. */
   int elements;
   /*! Maximum number of elements in the bucket. */
   int max_elements;
#endif   /* defined(AO2_DEBUG) */
};

/*!
 * A hash container in addition to values common to all
 * container types, stores the hash callback function, the
 * number of hash buckets, and the hash bucket heads.
 */
struct ao2_container_hash {
   /*!
    * \brief Items common to all containers.
    * \note Must be first in the specific container struct.
    */
   struct ao2_container common;
   ao2_hash_fn *hash_fn;
   /*! Number of hash buckets in this container. */
   int n_buckets;
   /*! Hash bucket array of n_buckets.  Variable size. */
   struct hash_bucket buckets[0];
};

/*! Traversal state to restart a hash container traversal. */
struct hash_traversal_state {
   /*! Active sort function in the traversal if not NULL. */
   ao2_sort_fn *sort_fn;
   /*! Saved comparison callback arg pointer. */
   void *arg;
   /*! Starting hash bucket */
   int bucket_start;
   /*! Stopping hash bucket */
   int bucket_last;
   /*! Saved search flags to control traversing the container. */
   enum search_flags flags;
   /*! TRUE if it is a descending search */
   unsigned int descending:1;
};

struct hash_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 hash_traversal_state))];
};

/*!
 * \internal
 * \brief Create an empty copy of this container.
 * \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 *hash_ao2_alloc_empty_clone(struct ao2_container_hash *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_hash(ao2_options_get(self), self->common.options,
      self->n_buckets, self->hash_fn, self->common.sort_fn, self->common.cmp_fn,
      tag, file, line, func);
}

/*!
 * \internal
 * \brief Destroy a hash container list 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 hash_ao2_node_destructor(void *v_doomed)
{
   struct hash_bucket_node *doomed = v_doomed;

   if (doomed->common.is_linked) {
      struct ao2_container_hash *my_container;
      struct hash_bucket *bucket;

      /*
       * 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_hash *) 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) */
      bucket = &my_container->buckets[doomed->my_bucket];
      AST_DLLIST_REMOVE(&bucket->list, doomed, links);
      AO2_DEVMODE_STAT(--my_container->common.nodes);
   }

   /*
    * 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 hash_bucket_node *hash_ao2_new_node(struct ao2_container_hash *self, void *obj_new, const char *tag, const char *file, int line, const char *func)
{
   struct hash_bucket_node *node;
   int i;

   node = ao2_alloc_options(sizeof(*node), hash_ao2_node_destructor,
      AO2_ALLOC_OPT_LOCK_NOLOCK | AO2_ALLOC_OPT_NO_REF_DEBUG);
   if (!node) {
      return NULL;
   }

   i = abs(self->hash_fn(obj_new, OBJ_SEARCH_OBJECT) % self->n_buckets);

   __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;
   node->my_bucket = i;

   return node;
}

/*!
 * \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 hash_ao2_insert_node(struct ao2_container_hash *self,
   struct hash_bucket_node *node)
{
   int cmp;
   struct hash_bucket *bucket;
   struct hash_bucket_node *cur;
   ao2_sort_fn *sort_fn;
   uint32_t options;

   bucket = &self->buckets[node->my_bucket];
   sort_fn = self->common.sort_fn;
   options = self->common.options;

   if (options & AO2_CONTAINER_ALLOC_OPT_INSERT_BEGIN) {
      if (sort_fn) {
         AST_DLLIST_TRAVERSE_BACKWARDS_SAFE_BEGIN(&bucket->list, cur, links) {
            cmp = sort_fn(cur->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp > 0) {
               continue;
            }
            if (cmp < 0) {
               AST_DLLIST_INSERT_AFTER_CURRENT(node, links);
               return AO2_CONTAINER_INSERT_NODE_INSERTED;
            }
            switch (options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
            default:
            case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
               break;
            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;
               }
               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;
            }
         }
         AST_DLLIST_TRAVERSE_BACKWARDS_SAFE_END;
      }
      AST_DLLIST_INSERT_HEAD(&bucket->list, node, links);
   } else {
      if (sort_fn) {
         AST_DLLIST_TRAVERSE_SAFE_BEGIN(&bucket->list, cur, links) {
            cmp = sort_fn(cur->common.obj, node->common.obj, OBJ_SEARCH_OBJECT);
            if (cmp < 0) {
               continue;
            }
            if (cmp > 0) {
               AST_DLLIST_INSERT_BEFORE_CURRENT(node, links);
               return AO2_CONTAINER_INSERT_NODE_INSERTED;
            }
            switch (options & AO2_CONTAINER_ALLOC_OPT_DUPS_MASK) {
            default:
            case AO2_CONTAINER_ALLOC_OPT_DUPS_ALLOW:
               break;
            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;
               }
               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;
            }
         }
         AST_DLLIST_TRAVERSE_SAFE_END;
      }
      AST_DLLIST_INSERT_TAIL(&bucket->list, node, links);
   }
   return AO2_CONTAINER_INSERT_NODE_INSERTED;
}

/*!
 * \internal
 * \brief Find the first hash 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 hash container traversal.
 *
 * \retval node-ptr of found node (Reffed).
 * \retval NULL when no node found.
 */
static struct hash_bucket_node *hash_ao2_find_first(struct ao2_container_hash *self, enum search_flags flags, void *arg, struct hash_traversal_state *state)
{
   struct hash_bucket_node *node;
   int bucket_cur;
   int cmp;

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

   /* Determine traversal order. */
   switch (flags & OBJ_ORDER_MASK) {
   case OBJ_ORDER_POST:
   case OBJ_ORDER_DESCENDING:
      state->descending = 1;
      break;
   case OBJ_ORDER_PRE:
   case OBJ_ORDER_ASCENDING:
   default:
      break;
   }

   /*
    * If lookup by pointer or search key, run the hash and optional
    * sort functions.  Otherwise, traverse the whole container.
    */
   switch (flags & OBJ_SEARCH_MASK) {
   case OBJ_SEARCH_OBJECT:
   case OBJ_SEARCH_KEY:
      /* we know hash can handle this case */
      bucket_cur = abs(self->hash_fn(arg, flags & OBJ_SEARCH_MASK)
            % self->n_buckets);
      state->sort_fn = self->common.sort_fn;
      break;
   case OBJ_SEARCH_PARTIAL_KEY:
      /* scan all buckets for partial key matches */
      bucket_cur = -1;
      state->sort_fn = self->common.sort_fn;
      break;
   default:
      /* don't know, let's scan all buckets */
      bucket_cur = -1;
      state->sort_fn = NULL;
      break;
   }

   if (state->descending) {
      /*
       * Determine the search boundaries of a descending traversal.
       *
       * bucket_cur downto state->bucket_last
       */
      if (bucket_cur < 0) {
         bucket_cur = self->n_buckets - 1;
         state->bucket_last = 0;
      } else {
         state->bucket_last = bucket_cur;
      }
      state->bucket_start = bucket_cur;

      /* For each bucket */
      for (; state->bucket_last <= bucket_cur; --bucket_cur) {
         /* For each node in the bucket. */
         for (node = AST_DLLIST_LAST(&self->buckets[bucket_cur].list);
            node;
            node = AST_DLLIST_PREV(node, links)) {
            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 > 0) {
                  continue;
               }
               if (cmp < 0) {
                  /* No more nodes in this bucket are possible to match. */
                  break;
               }
            }

            /* We have the first traversal node */
            ao2_ref(node, +1);
            return node;
         }
      }
   } else {
      /*
       * Determine the search boundaries of an ascending traversal.
       *
       * bucket_cur to state->bucket_last-1
       */
      if (bucket_cur < 0) {
         bucket_cur = 0;
         state->bucket_last = self->n_buckets;
      } else {
         state->bucket_last = bucket_cur + 1;
      }
      state->bucket_start = bucket_cur;

      /* For each bucket */
      for (; bucket_cur < state->bucket_last; ++bucket_cur) {
         /* For each node in the bucket. */
         for (node = AST_DLLIST_FIRST(&self->buckets[bucket_cur].list);
            node;
            node = AST_DLLIST_NEXT(node, links)) {
            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 < 0) {
                  continue;
               }
               if (cmp > 0) {
                  /* No more nodes in this bucket are possible to match. */
                  break;
               }
            }

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

   return NULL;
}

/*!
 * \internal
 * \brief Find the next hash container node in a traversal.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 * \param state Traversal state to restart hash 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 hash_bucket_node *hash_ao2_find_next(struct ao2_container_hash *self, struct hash_traversal_state *state, struct hash_bucket_node *prev)
{
   struct hash_bucket_node *node;
   void *arg;
   enum search_flags flags;
   int bucket_cur;
   int cmp;

   arg = state->arg;
   flags = state->flags;
   bucket_cur = prev->my_bucket;
   node = prev;

   /*
    * This function is structured the same as hash_ao2_find_first()
    * intentionally.  We are resuming the search loops from
    * hash_ao2_find_first() in order to find the next node.  The
    * search loops must be resumed where hash_ao2_find_first()
    * returned with the first node.
    */
   if (state->descending) {
      goto hash_descending_resume;

      /* For each bucket */
      for (; state->bucket_last <= bucket_cur; --bucket_cur) {
         /* For each node in the bucket. */
         for (node = AST_DLLIST_LAST(&self->buckets[bucket_cur].list);
            node;
            node = AST_DLLIST_PREV(node, links)) {
            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 > 0) {
                  continue;
               }
               if (cmp < 0) {
                  /* No more nodes in this bucket 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;

hash_descending_resume:;
         }
      }
   } else {
      goto hash_ascending_resume;

      /* For each bucket */
      for (; bucket_cur < state->bucket_last; ++bucket_cur) {
         /* For each node in the bucket. */
         for (node = AST_DLLIST_FIRST(&self->buckets[bucket_cur].list);
            node;
            node = AST_DLLIST_NEXT(node, links)) {
            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 < 0) {
                  continue;
               }
               if (cmp > 0) {
                  /* No more nodes in this bucket 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;

hash_ascending_resume:;
         }
      }
   }

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

/*!
 * \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 hash_bucket_node *hash_ao2_iterator_next(struct ao2_container_hash *self, struct hash_bucket_node *node, enum ao2_iterator_flags flags)
{
   int cur_bucket;

   if (flags & AO2_ITERATOR_DESCENDING) {
      if (node) {
         cur_bucket = node->my_bucket;

         /* Find next non-empty node. */
         for (;;) {
            node = AST_DLLIST_PREV(node, links);
            if (!node) {
               break;
            }
            if (node->common.obj) {
               /* Found a non-empty node. */
               return node;
            }
         }
      } else {
         /* Find first non-empty node. */
         cur_bucket = self->n_buckets;
      }

      /* Find a non-empty node in the remaining buckets */
      while (0 <= --cur_bucket) {
         node = AST_DLLIST_LAST(&self->buckets[cur_bucket].list);
         while (node) {
            if (node->common.obj) {
               /* Found a non-empty node. */
               return node;
            }
            node = AST_DLLIST_PREV(node, links);
         }
      }
   } else {
      if (node) {
         cur_bucket = node->my_bucket;

         /* Find next non-empty node. */
         for (;;) {
            node = AST_DLLIST_NEXT(node, links);
            if (!node) {
               break;
            }
            if (node->common.obj) {
               /* Found a non-empty node. */
               return node;
            }
         }
      } else {
         /* Find first non-empty node. */
         cur_bucket = -1;
      }

      /* Find a non-empty node in the remaining buckets */
      while (++cur_bucket < self->n_buckets) {
         node = AST_DLLIST_FIRST(&self->buckets[cur_bucket].list);
         while (node) {
            if (node->common.obj) {
               /* Found a non-empty node. */
               return node;
            }
            node = AST_DLLIST_NEXT(node, links);
         }
      }
   }

   /* No more nodes to visit in the container. */
   return NULL;
}

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Increment the hash container linked object statistic.
 * \since 12.0.0
 *
 * \param hash Container to operate upon.
 * \param hash_node Container node linking object to.
 *
 * \return Nothing
 */
static void hash_ao2_link_node_stat(struct ao2_container *hash, struct ao2_container_node *hash_node)
{
   struct ao2_container_hash *self = (struct ao2_container_hash *) hash;
   struct hash_bucket_node *node = (struct hash_bucket_node *) hash_node;
   int i = node->my_bucket;

   ++self->buckets[i].elements;
   if (self->buckets[i].max_elements < self->buckets[i].elements) {
      self->buckets[i].max_elements = self->buckets[i].elements;
   }
}
#endif   /* defined(AO2_DEBUG) */

#if defined(AO2_DEBUG)
/*!
 * \internal
 * \brief Decrement the hash container linked object statistic.
 * \since 12.0.0
 *
 * \param hash Container to operate upon.
 * \param hash_node Container node unlinking object from.
 *
 * \return Nothing
 */
static void hash_ao2_unlink_node_stat(struct ao2_container *hash, struct ao2_container_node *hash_node)
{
   struct ao2_container_hash *self = (struct ao2_container_hash *) hash;
   struct hash_bucket_node *node = (struct hash_bucket_node *) hash_node;

   --self->buckets[node->my_bucket].elements;
}
#endif   /* defined(AO2_DEBUG) */

/*!
 * \internal
 *
 * \brief Destroy this container.
 * \since 12.0.0
 *
 * \param self Container to operate upon.
 *
 * \return Nothing
 */
static void hash_ao2_destroy(struct ao2_container_hash *self)
{
   int idx;

   /* Check that the container no longer has any nodes */
   for (idx = self->n_buckets; idx--;) {
      if (!AST_DLLIST_EMPTY(&self->buckets[idx].list)) {
         ast_log(LOG_ERROR, "Node ref leak.  Hash container still has nodes!\n");
         ast_assert(0);
         break;
      }
   }
}

#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 hash_ao2_dump(struct ao2_container_hash *self, void *where, ao2_prnt_fn *prnt, ao2_prnt_obj_fn *prnt_obj)
{
#define FORMAT  "%6s, %16s, %16s, %16s, %16s, %s\n"
#define FORMAT2 "%6d, %16p, %16p, %16p, %16p, "

   int bucket;
   int suppressed_buckets = 0;
   struct hash_bucket_node *node;

   prnt(where, "Number of buckets: %d\n\n", self->n_buckets);

   prnt(where, FORMAT, "Bucket", "Node", "Prev", "Next", "Obj", "Key");
   for (bucket = 0; bucket < self->n_buckets; ++bucket) {
      node = AST_DLLIST_FIRST(&self->buckets[bucket].list);
      if (node) {
         suppressed_buckets = 0;
         do {
            prnt(where, FORMAT2,
               bucket,
               node,
               AST_DLLIST_PREV(node, links),
               AST_DLLIST_NEXT(node, links),
               node->common.obj);
            if (node->common.obj && prnt_obj) {
               prnt_obj(node->common.obj, where, prnt);
            }
            prnt(where, "\n");

            node = AST_DLLIST_NEXT(node, links);
         } while (node);
      } else if (!suppressed_buckets) {
         suppressed_buckets = 1;
         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 hash_ao2_stats(struct ao2_container_hash *self, void *where, ao2_prnt_fn *prnt)
{
#define FORMAT  "%10.10s %10.10s %10.10s\n"
#define FORMAT2 "%10d %10d %10d\n"

   int bucket;
   int suppressed_buckets = 0;

   prnt(where, "Number of buckets: %d\n\n", self->n_buckets);

   prnt(where, FORMAT, "Bucket", "Objects", "Max");
   for (bucket = 0; bucket < self->n_buckets; ++bucket) {
      if (self->buckets[bucket].max_elements) {
         suppressed_buckets = 0;
         prnt(where, FORMAT2, bucket, self->buckets[bucket].elements,
            self->buckets[bucket].max_elements);
      } else if (!suppressed_buckets) {
         suppressed_buckets = 1;
         prnt(where, "...\n");
      }
   }

#undef FORMAT
#undef FORMAT2
}
#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 hash_ao2_integrity(struct ao2_container_hash *self)
{
   int bucket_exp;
   int bucket;
   int count_obj;
   int count_total_obj;
   int count_total_node;
   void *obj_last;
   struct hash_bucket_node *node;
   struct hash_bucket_node *prev;
   struct hash_bucket_node *next;

   count_total_obj = 0;
   count_total_node = 0;

   /* For each bucket in the container. */
   for (bucket = 0; bucket < self->n_buckets; ++bucket) {
      if (!AST_DLLIST_FIRST(&self->buckets[bucket].list)
         && !AST_DLLIST_LAST(&self->buckets[bucket].list)) {
         /* The bucket list is empty. */
         continue;
      }

      count_obj = 0;
      obj_last = NULL;

      /* Check bucket list links and nodes. */
      node = AST_DLLIST_LAST(&self->buckets[bucket].list);
      if (!node) {
         ast_log(LOG_ERROR, "Bucket %d list tail is NULL when it should not be!\n",
            bucket);
         return -1;
      }
      if (AST_DLLIST_NEXT(node, links)) {
         ast_log(LOG_ERROR, "Bucket %d list tail node is not the last node!\n",
            bucket);
         return -1;
      }
      node = AST_DLLIST_FIRST(&self->buckets[bucket].list);
      if (!node) {
         ast_log(LOG_ERROR, "Bucket %d list head is NULL when it should not be!\n",
            bucket);
         return -1;
      }
      if (AST_DLLIST_PREV(node, links)) {
         ast_log(LOG_ERROR, "Bucket %d list head node is not the first node!\n",
            bucket);
         return -1;
      }
      for (; node; node = next) {
         /* Check backward link. */
         prev = AST_DLLIST_PREV(node, links);
         if (prev) {
            if (prev == node) {
               ast_log(LOG_ERROR, "Bucket %d list node's prev pointer points to itself!\n",
                  bucket);
               return -1;
            }
            if (node != AST_DLLIST_NEXT(prev, links)) {
               ast_log(LOG_ERROR, "Bucket %d list node's prev node does not link back!\n",
                  bucket);
               return -1;
            }
         } else if (node != AST_DLLIST_FIRST(&self->buckets[bucket].list)) {
            ast_log(LOG_ERROR, "Bucket %d backward list chain is broken!\n",
               bucket);
            return -1;
         }

         /* Check forward link. */
         next = AST_DLLIST_NEXT(node, links);
         if (next) {
            if (next == node) {
               ast_log(LOG_ERROR, "Bucket %d list node's next pointer points to itself!\n",
                  bucket);
               return -1;
            }
            if (node != AST_DLLIST_PREV(next, links)) {
               ast_log(LOG_ERROR, "Bucket %d list node's next node does not link back!\n",
                  bucket);
               return -1;
            }
         } else if (node != AST_DLLIST_LAST(&self->buckets[bucket].list)) {
            ast_log(LOG_ERROR, "Bucket %d forward list chain is broken!\n",
               bucket);
            return -1;
         }

         if (bucket != node->my_bucket) {
            ast_log(LOG_ERROR, "Bucket %d node claims to be in bucket %d!\n",
               bucket, node->my_bucket);
            return -1;
         }

         ++count_total_node;
         if (!node->common.obj) {
            /* Node is empty. */
            continue;
         }
         ++count_obj;

         /* Check container hash key for expected bucket. */
         bucket_exp = abs(self->hash_fn(node->common.obj, OBJ_SEARCH_OBJECT)
               % self->n_buckets);
         if (bucket != bucket_exp) {
            ast_log(LOG_ERROR, "Bucket %d node hashes to bucket %d!\n",
               bucket, bucket_exp);
            return -1;
         }

         /* Check sort if configured. */
         if (self->common.sort_fn) {
            if (obj_last
               && self->common.sort_fn(obj_last, node->common.obj, OBJ_SEARCH_OBJECT) > 0) {
               ast_log(LOG_ERROR, "Bucket %d nodes out of sorted order!\n",
                  bucket);
               return -1;
            }
            obj_last = node->common.obj;
         }
      }

      /* Check bucket obj count statistic. */
      if (count_obj != self->buckets[bucket].elements) {
         ast_log(LOG_ERROR, "Bucket %d object count of %d does not match stat of %d!\n",
            bucket, count_obj, self->buckets[bucket].elements);
         return -1;
      }

      /* Accumulate found object counts. */
      count_total_obj += count_obj;
   }

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

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

   return 0;
}
#endif   /* defined(AO2_DEBUG) */

/*! Hash container virtual method table. */
static const struct ao2_container_methods v_table_hash = {
   .alloc_empty_clone = (ao2_container_alloc_empty_clone_fn) hash_ao2_alloc_empty_clone,
   .new_node = (ao2_container_new_node_fn) hash_ao2_new_node,
   .insert = (ao2_container_insert_fn) hash_ao2_insert_node,
   .traverse_first = (ao2_container_find_first_fn) hash_ao2_find_first,
   .traverse_next = (ao2_container_find_next_fn) hash_ao2_find_next,
   .iterator_next = (ao2_iterator_next_fn) hash_ao2_iterator_next,
   .destroy = (ao2_container_destroy_fn) hash_ao2_destroy,
#if defined(AO2_DEBUG)
   .link_stat = hash_ao2_link_node_stat,
   .unlink_stat = hash_ao2_unlink_node_stat,
   .dump = (ao2_container_display) hash_ao2_dump,
   .stats = (ao2_container_statistics) hash_ao2_stats,
   .integrity = (ao2_container_integrity) hash_ao2_integrity,
#endif   /* defined(AO2_DEBUG) */
};

/*!
 * \brief always zero hash function
 *
 * it is convenient to have a hash function that always returns 0.
 * This is basically used when we want to have a container that is
 * a simple linked list.
 *
 * \returns 0
 */
static int hash_zero(const void *user_obj, const int flags)
{
   return 0;
}

/*!
 * \brief Initialize a hash container with the desired number of buckets.
 *
 * \param self Container to initialize.
 * \param options Container behaviour options (See enum ao2_container_opts)
 * \param n_buckets Number of buckets for hash
 * \param hash_fn Pointer to a function computing a hash value.
 * \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 *hash_ao2_container_init(
   struct ao2_container_hash *self, unsigned int options, unsigned int n_buckets,
   ao2_hash_fn *hash_fn, ao2_sort_fn *sort_fn, ao2_callback_fn *cmp_fn)
{
   if (!self) {
      return NULL;
   }

   self->common.v_table = &v_table_hash;
   self->common.sort_fn = sort_fn;
   self->common.cmp_fn = cmp_fn;
   self->common.options = options;
   self->hash_fn = hash_fn ? hash_fn : hash_zero;
   self->n_buckets = n_buckets;

#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_hash(unsigned int ao2_options,
   unsigned int container_options, unsigned int n_buckets, ao2_hash_fn *hash_fn,
   ao2_sort_fn *sort_fn, ao2_callback_fn *cmp_fn,
   const char *tag, const char *file, int line, const char *func)
{
   unsigned int num_buckets;
   size_t container_size;
   struct ao2_container_hash *self;

   num_buckets = hash_fn ? n_buckets : 1;
   container_size = sizeof(struct ao2_container_hash) + num_buckets * sizeof(struct hash_bucket);

   self = __ao2_alloc(container_size, container_destruct, ao2_options,
      tag ?: __PRETTY_FUNCTION__, file, line, func);
   return hash_ao2_container_init(self, container_options, num_buckets, hash_fn,
      sort_fn, cmp_fn);
}

struct ao2_container *__ao2_container_alloc_list(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)
{
   return __ao2_container_alloc_hash(ao2_options, container_options, 1, NULL,
      sort_fn, cmp_fn, tag, file, line, func);
}