stasis_cache.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2013, Digium, Inc.
 *
 * David M. Lee, II <dlee@digium.com>
 *
 * 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 Stasis Message API.
 *
 * \author David M. Lee, II <dlee@digium.com>
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/astobj2.h"
#include "asterisk/hashtab.h"
#include "asterisk/stasis_internal.h"
#include "asterisk/stasis.h"
#include "asterisk/utils.h"
#include "asterisk/vector.h"
 
#ifdef LOW_MEMORY
#define NUM_CACHE_BUCKETS 17
#else
#define NUM_CACHE_BUCKETS 563
#endif
 
/*! \internal */
struct stasis_cache {
    struct ao2_container *entries;
    snapshot_get_id id_fn;
    cache_aggregate_calc_fn aggregate_calc_fn;
    cache_aggregate_publish_fn aggregate_publish_fn;
    int registered;
};
 
/*! \internal */
struct stasis_caching_topic {
    struct stasis_cache *cache;
    struct stasis_topic *topic;
    struct stasis_topic *original_topic;
    struct stasis_subscription *sub;
};
 
static void stasis_caching_topic_dtor(void *obj)
{
    struct stasis_caching_topic *caching_topic = obj;
 
    /* Caching topics contain subscriptions, and must be manually
     * unsubscribed. */
    ast_assert(!stasis_subscription_is_subscribed(caching_topic->sub));
    /* If there are any messages in flight to this subscription; that would
     * be bad. */
    ast_assert(stasis_subscription_is_done(caching_topic->sub));
 
    ao2_container_unregister(stasis_topic_name(caching_topic->topic));
 
    ao2_cleanup(caching_topic->sub);
    caching_topic->sub = NULL;
    ao2_cleanup(caching_topic->cache);
    caching_topic->cache = NULL;
    ao2_cleanup(caching_topic->topic);
    caching_topic->topic = NULL;
    ao2_cleanup(caching_topic->original_topic);
    caching_topic->original_topic = NULL;
}
 
struct stasis_topic *stasis_caching_get_topic(struct stasis_caching_topic *caching_topic)
{
    return caching_topic->topic;
}
 
int stasis_caching_accept_message_type(struct stasis_caching_topic *caching_topic,
    struct stasis_message_type *type)
{
    int res;
 
    if (!caching_topic) {
        return -1;
    }
 
    /* We wait to accept the stasis specific message types until now so that by default everything
     * will flow to us.
     */
    res = stasis_subscription_accept_message_type(caching_topic->sub, stasis_cache_clear_type());
    res |= stasis_subscription_accept_message_type(caching_topic->sub, stasis_subscription_change_type());
    res |= stasis_subscription_accept_message_type(caching_topic->sub, type);
 
    return res;
}
 
int stasis_caching_set_filter(struct stasis_caching_topic *caching_topic,
    enum stasis_subscription_message_filter filter)
{
    if (!caching_topic) {
        return -1;
    }
    return stasis_subscription_set_filter(caching_topic->sub, filter);
}
 
 
struct stasis_caching_topic *stasis_caching_unsubscribe(struct stasis_caching_topic *caching_topic)
{
    if (!caching_topic) {
        return NULL;
    }
 
    /*
     * The subscription may hold the last reference to this caching
     * topic, but we want to make sure the unsubscribe finishes
     * before kicking of the caching topic's dtor.
     */
    ao2_ref(caching_topic, +1);
 
    if (stasis_subscription_is_subscribed(caching_topic->sub)) {
        /*
         * Increment the reference to hold on to it past the
         * unsubscribe. Will be cleaned up in dtor.
         */
        ao2_ref(caching_topic->sub, +1);
        stasis_unsubscribe(caching_topic->sub);
    } else {
        ast_log(LOG_ERROR, "stasis_caching_topic unsubscribed multiple times\n");
    }
    ao2_cleanup(caching_topic);
    return NULL;
}
 
struct stasis_caching_topic *stasis_caching_unsubscribe_and_join(struct stasis_caching_topic *caching_topic)
{
    if (!caching_topic) {
        return NULL;
    }
 
    /* Hold a ref past the unsubscribe */
    ao2_ref(caching_topic, +1);
    stasis_caching_unsubscribe(caching_topic);
    stasis_subscription_join(caching_topic->sub);
    ao2_cleanup(caching_topic);
    return NULL;
}
 
/*!
 * \brief The key for an entry in the cache
 * \note The items in this struct must be immutable for the item in the cache
 */
struct cache_entry_key {
    /*! The message type of the item stored in the cache */
    struct stasis_message_type *type;
    /*! The unique ID of the item stored in the cache */
    const char *id;
    /*! The hash, computed from \c type and \c id */
    unsigned int hash;
};
 
struct stasis_cache_entry {
    struct cache_entry_key key;
    /*! Aggregate snapshot of the stasis cache. */
    struct stasis_message *aggregate;
    /*! Local entity snapshot of the stasis event. */
    struct stasis_message *local;
    /*! Remote entity snapshots of the stasis event. */
    AST_VECTOR(, struct stasis_message *) remote;
};
 
static void cache_entry_dtor(void *obj)
{
    struct stasis_cache_entry *entry = obj;
    size_t idx;
 
    entry->key.type = NULL;
    ast_free((char *) entry->key.id);
    entry->key.id = NULL;
 
    ao2_cleanup(entry->aggregate);
    entry->aggregate = NULL;
    ao2_cleanup(entry->local);
    entry->local = NULL;
 
    for (idx = 0; idx < AST_VECTOR_SIZE(&entry->remote); ++idx) {
        struct stasis_message *remote;
 
        remote = AST_VECTOR_GET(&entry->remote, idx);
        ao2_cleanup(remote);
    }
    AST_VECTOR_FREE(&entry->remote);
}
 
static void cache_entry_compute_hash(struct cache_entry_key *key)
{
    key->hash = stasis_message_type_hash(key->type);
    key->hash += ast_hashtab_hash_string(key->id);
}
 
static struct stasis_cache_entry *cache_entry_create(struct stasis_message_type *type, const char *id, struct stasis_message *snapshot)
{
    struct stasis_cache_entry *entry;
    int is_remote;
 
    ast_assert(id != NULL);
    ast_assert(snapshot != NULL);
 
    if (!type) {
        return NULL;
    }
 
    entry = ao2_alloc_options(sizeof(*entry), cache_entry_dtor,
        AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!entry) {
        return NULL;
    }
 
    entry->key.id = ast_strdup(id);
    if (!entry->key.id) {
        ao2_cleanup(entry);
        return NULL;
    }
    /*
     * Normal ao2 ref counting rules says we should increment the message
     * type ref here and decrement it in cache_entry_dtor().  However, the
     * stasis message snapshot is cached here, will always have the same type
     * as the cache entry, and can legitimately cause the type ref count to
     * hit the excessive ref count assertion.  Since the cache entry will
     * always have a snapshot we can get away with not holding a ref here.
     */
    ast_assert(type == stasis_message_type(snapshot));
    entry->key.type = type;
    cache_entry_compute_hash(&entry->key);
 
    is_remote = ast_eid_cmp(&ast_eid_default, stasis_message_eid(snapshot)) ? 1 : 0;
    if (AST_VECTOR_INIT(&entry->remote, is_remote)) {
        ao2_cleanup(entry);
        return NULL;
    }
 
    if (is_remote) {
        if (AST_VECTOR_APPEND(&entry->remote, snapshot)) {
            ao2_cleanup(entry);
            return NULL;
        }
    } else {
        entry->local = snapshot;
    }
    ao2_bump(snapshot);
 
    return entry;
}
 
static int cache_entry_hash(const void *obj, int flags)
{
    const struct stasis_cache_entry *object;
    const struct cache_entry_key *key;
 
    switch (flags & OBJ_SEARCH_MASK) {
    case OBJ_SEARCH_KEY:
        key = obj;
        break;
    case OBJ_SEARCH_OBJECT:
        object = obj;
        key = &object->key;
        break;
    default:
        /* Hash can only work on something with a full key. */
        ast_assert(0);
        return 0;
    }
 
    return (int)key->hash;
}
 
static int cache_entry_cmp(void *obj, void *arg, int flags)
{
    const struct stasis_cache_entry *object_left = obj;
    const struct stasis_cache_entry *object_right = arg;
    const struct cache_entry_key *right_key = arg;
    int cmp;
 
    switch (flags & OBJ_SEARCH_MASK) {
    case OBJ_SEARCH_OBJECT:
        right_key = &object_right->key;
        /* Fall through */
    case OBJ_SEARCH_KEY:
        cmp = object_left->key.type != right_key->type
            || strcmp(object_left->key.id, right_key->id);
        break;
    case OBJ_SEARCH_PARTIAL_KEY:
        /* Not supported by container */
        ast_assert(0);
        cmp = -1;
        break;
    default:
        /*
         * What arg points to is specific to this traversal callback
         * and has no special meaning to astobj2.
         */
        cmp = 0;
        break;
    }
    if (cmp) {
        return 0;
    }
    /*
     * At this point the traversal callback is identical to a sorted
     * container.
     */
    return CMP_MATCH;
}
 
static void cache_dtor(void *obj)
{
    struct stasis_cache *cache = obj;
 
    ao2_cleanup(cache->entries);
    cache->entries = NULL;
}
 
struct stasis_cache *stasis_cache_create_full(snapshot_get_id id_fn,
    cache_aggregate_calc_fn aggregate_calc_fn,
    cache_aggregate_publish_fn aggregate_publish_fn)
{
    struct stasis_cache *cache;
 
    cache = ao2_alloc_options(sizeof(*cache), cache_dtor,
        AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!cache) {
        return NULL;
    }
 
    cache->entries = ao2_container_alloc_hash(AO2_ALLOC_OPT_LOCK_RWLOCK, 0,
        NUM_CACHE_BUCKETS, cache_entry_hash, NULL, cache_entry_cmp);
    if (!cache->entries) {
        ao2_cleanup(cache);
        return NULL;
    }
 
    cache->id_fn = id_fn;
    cache->aggregate_calc_fn = aggregate_calc_fn;
    cache->aggregate_publish_fn = aggregate_publish_fn;
 
    return cache;
}
 
struct stasis_cache *stasis_cache_create(snapshot_get_id id_fn)
{
    return stasis_cache_create_full(id_fn, NULL, NULL);
}
 
struct stasis_message *stasis_cache_entry_get_aggregate(struct stasis_cache_entry *entry)
{
    return entry->aggregate;
}
 
struct stasis_message *stasis_cache_entry_get_local(struct stasis_cache_entry *entry)
{
    return entry->local;
}
 
struct stasis_message *stasis_cache_entry_get_remote(struct stasis_cache_entry *entry, int idx)
{
    if (idx < AST_VECTOR_SIZE(&entry->remote)) {
        return AST_VECTOR_GET(&entry->remote, idx);
    }
    return NULL;
}
 
/*!
 * \internal
 * \brief Find the cache entry in the cache entries container.
 *
 * \param entries Container of cached entries.
 * \param type Type of message to retrieve the cache entry.
 * \param id Identity of the snapshot to retrieve the cache entry.
 *
 * \note The entries container is already locked.
 *
 * \return Cache-entry on success.
 * \retval NULL Not in cache.
 */
static struct stasis_cache_entry *cache_find(struct ao2_container *entries, struct stasis_message_type *type, const char *id)
{
    struct cache_entry_key search_key;
    struct stasis_cache_entry *entry;
 
    search_key.type = type;
    search_key.id = id;
    cache_entry_compute_hash(&search_key);
    entry = ao2_find(entries, &search_key, OBJ_SEARCH_KEY | OBJ_NOLOCK);
 
    /* Ensure that what we looked for is what we found. */
    ast_assert(!entry
        || (!strcmp(stasis_message_type_name(entry->key.type),
            stasis_message_type_name(type)) && !strcmp(entry->key.id, id)));
    return entry;
}
 
/*!
 * \internal
 * \brief Remove the stasis snapshot in the cache entry determined by eid.
 *
 * \param entries Container of cached entries.
 * \param cached_entry The entry to remove the snapshot from.
 * \param eid Which snapshot in the cached entry.
 *
 * \note The entries container is already locked.
 *
 * \return Previous stasis entry snapshot.
 */
static struct stasis_message *cache_remove(struct ao2_container *entries, struct stasis_cache_entry *cached_entry, const struct ast_eid *eid)
{
    struct stasis_message *old_snapshot;
    int is_remote;
 
    is_remote = ast_eid_cmp(eid, &ast_eid_default);
    if (!is_remote) {
        old_snapshot = cached_entry->local;
        cached_entry->local = NULL;
    } else {
        int idx;
 
        old_snapshot = NULL;
        for (idx = 0; idx < AST_VECTOR_SIZE(&cached_entry->remote); ++idx) {
            struct stasis_message *cur;
 
            cur = AST_VECTOR_GET(&cached_entry->remote, idx);
            if (!ast_eid_cmp(eid, stasis_message_eid(cur))) {
                old_snapshot = AST_VECTOR_REMOVE_UNORDERED(&cached_entry->remote, idx);
                break;
            }
        }
    }
 
    if (!cached_entry->local && !AST_VECTOR_SIZE(&cached_entry->remote)) {
        ao2_unlink_flags(entries, cached_entry, OBJ_NOLOCK);
    }
 
    return old_snapshot;
}
 
/*!
 * \internal
 * \brief Update the stasis snapshot in the cache entry determined by eid.
 *
 * \param cached_entry The entry to remove the snapshot from.
 * \param eid Which snapshot in the cached entry.
 * \param new_snapshot Snapshot to replace the old snapshot.
 *
 * \return Previous stasis entry snapshot.
 */
static struct stasis_message *cache_update(struct stasis_cache_entry *cached_entry, const struct ast_eid *eid, struct stasis_message *new_snapshot)
{
    struct stasis_message *old_snapshot;
    int is_remote;
    int idx;
 
    is_remote = ast_eid_cmp(eid, &ast_eid_default);
    if (!is_remote) {
        old_snapshot = cached_entry->local;
        cached_entry->local = ao2_bump(new_snapshot);
        return old_snapshot;
    }
 
    old_snapshot = NULL;
    for (idx = 0; idx < AST_VECTOR_SIZE(&cached_entry->remote); ++idx) {
        struct stasis_message *cur;
 
        cur = AST_VECTOR_GET(&cached_entry->remote, idx);
        if (!ast_eid_cmp(eid, stasis_message_eid(cur))) {
            old_snapshot = AST_VECTOR_REMOVE_UNORDERED(&cached_entry->remote, idx);
            break;
        }
    }
    if (!AST_VECTOR_APPEND(&cached_entry->remote, new_snapshot)) {
        ao2_bump(new_snapshot);
    }
 
    return old_snapshot;
}
 
struct cache_put_snapshots {
    /*! Old cache eid snapshot. */
    struct stasis_message *old;
    /*! Old cache aggregate snapshot. */
    struct stasis_message *aggregate_old;
    /*! New cache aggregate snapshot. */
    struct stasis_message *aggregate_new;
};
 
static struct cache_put_snapshots cache_put(struct stasis_cache *cache,
    struct stasis_message_type *type, const char *id, const struct ast_eid *eid,
    struct stasis_message *new_snapshot)
{
    struct stasis_cache_entry *cached_entry;
    struct cache_put_snapshots snapshots;
 
    ast_assert(cache->entries != NULL);
    ast_assert(eid != NULL);/* Aggregate snapshots not allowed to be put directly. */
    ast_assert(new_snapshot == NULL ||
        type == stasis_message_type(new_snapshot));
 
    memset(&snapshots, 0, sizeof(snapshots));
 
    ao2_wrlock(cache->entries);
 
    cached_entry = cache_find(cache->entries, type, id);
 
    /* Update the eid snapshot. */
    if (!new_snapshot) {
        /* Remove snapshot from cache */
        if (cached_entry) {
            snapshots.old = cache_remove(cache->entries, cached_entry, eid);
        }
    } else if (cached_entry) {
        /* Update snapshot in cache */
        snapshots.old = cache_update(cached_entry, eid, new_snapshot);
    } else {
        /* Insert into the cache */
        cached_entry = cache_entry_create(type, id, new_snapshot);
        if (cached_entry) {
            ao2_link_flags(cache->entries, cached_entry, OBJ_NOLOCK);
        }
    }
 
    /* Update the aggregate snapshot. */
    if (cache->aggregate_calc_fn && cached_entry) {
        snapshots.aggregate_new = cache->aggregate_calc_fn(cached_entry, new_snapshot);
        snapshots.aggregate_old = cached_entry->aggregate;
        cached_entry->aggregate = ao2_bump(snapshots.aggregate_new);
    }
 
    ao2_unlock(cache->entries);
 
    ao2_cleanup(cached_entry);
    return snapshots;
}
 
/*!
 * \internal
 * \brief Dump all entity snapshots in the cache entry into the given container.
 *
 * \param snapshots Container to put all snapshots in the cache entry.
 * \param entry Cache entry to use.
 *
 * \retval 0 on success.
 * \retval non-zero on error.
 */
static int cache_entry_dump(struct ao2_container *snapshots, const struct stasis_cache_entry *entry)
{
    int idx;
    int err = 0;
 
    ast_assert(snapshots != NULL);
    ast_assert(entry != NULL);
 
    /* The aggregate snapshot is not a snapshot from an entity. */
 
    if (entry->local) {
        err |= !ao2_link(snapshots, entry->local);
    }
 
    for (idx = 0; !err && idx < AST_VECTOR_SIZE(&entry->remote); ++idx) {
        struct stasis_message *snapshot;
 
        snapshot = AST_VECTOR_GET(&entry->remote, idx);
        err |= !ao2_link(snapshots, snapshot);
    }
 
    return err;
}
 
struct ao2_container *stasis_cache_get_all(struct stasis_cache *cache, struct stasis_message_type *type, const char *id)
{
    struct stasis_cache_entry *cached_entry;
    struct ao2_container *found;
 
    ast_assert(cache != NULL);
    ast_assert(cache->entries != NULL);
    ast_assert(id != NULL);
 
    if (!type) {
        return NULL;
    }
 
    found = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_NOLOCK, 0, NULL, NULL);
    if (!found) {
        return NULL;
    }
 
    ao2_rdlock(cache->entries);
 
    cached_entry = cache_find(cache->entries, type, id);
    if (cached_entry && cache_entry_dump(found, cached_entry)) {
        ao2_cleanup(found);
        found = NULL;
    }
 
    ao2_unlock(cache->entries);
 
    ao2_cleanup(cached_entry);
    return found;
}
 
/*!
 * \internal
 * \brief Retrieve an item from the cache entry for a specific eid.
 *
 * \param entry Cache entry to use.
 * \param eid Specific entity id to retrieve.  NULL for aggregate.
 *
 * \note The returned snapshot has not had its reference bumped.
 *
 * \return Snapshot from the cache.
 * \retval NULL if snapshot is not found.
 */
static struct stasis_message *cache_entry_by_eid(const struct stasis_cache_entry *entry, const struct ast_eid *eid)
{
    int is_remote;
    int idx;
 
    if (!eid) {
        /* Get aggregate. */
        return entry->aggregate;
    }
 
    /* Get snapshot with specific eid. */
    is_remote = ast_eid_cmp(eid, &ast_eid_default);
    if (!is_remote) {
        return entry->local;
    }
 
    for (idx = 0; idx < AST_VECTOR_SIZE(&entry->remote); ++idx) {
        struct stasis_message *cur;
 
        cur = AST_VECTOR_GET(&entry->remote, idx);
        if (!ast_eid_cmp(eid, stasis_message_eid(cur))) {
            return cur;
        }
    }
 
    return NULL;
}
 
struct stasis_message *stasis_cache_get_by_eid(struct stasis_cache *cache, struct stasis_message_type *type, const char *id, const struct ast_eid *eid)
{
    struct stasis_cache_entry *cached_entry;
    struct stasis_message *snapshot = NULL;
 
    ast_assert(cache != NULL);
    ast_assert(cache->entries != NULL);
    ast_assert(id != NULL);
 
    if (!type) {
        return NULL;
    }
 
    ao2_rdlock(cache->entries);
 
    cached_entry = cache_find(cache->entries, type, id);
    if (cached_entry) {
        snapshot = cache_entry_by_eid(cached_entry, eid);
        ao2_bump(snapshot);
    }
 
    ao2_unlock(cache->entries);
 
    ao2_cleanup(cached_entry);
    return snapshot;
}
 
struct stasis_message *stasis_cache_get(struct stasis_cache *cache, struct stasis_message_type *type, const char *id)
{
    return stasis_cache_get_by_eid(cache, type, id, &ast_eid_default);
}
 
struct cache_dump_data {
    struct ao2_container *container;
    struct stasis_message_type *type;
    const struct ast_eid *eid;
};
 
static int cache_dump_by_eid_cb(void *obj, void *arg, int flags)
{
    struct cache_dump_data *cache_dump = arg;
    struct stasis_cache_entry *entry = obj;
 
    if (!cache_dump->type || entry->key.type == cache_dump->type) {
        struct stasis_message *snapshot;
 
        snapshot = cache_entry_by_eid(entry, cache_dump->eid);
        if (snapshot) {
            if (!ao2_link(cache_dump->container, snapshot)) {
                ao2_cleanup(cache_dump->container);
                cache_dump->container = NULL;
                return CMP_STOP;
            }
        }
    }
 
    return 0;
}
 
struct ao2_container *stasis_cache_dump_by_eid(struct stasis_cache *cache, struct stasis_message_type *type, const struct ast_eid *eid)
{
    struct cache_dump_data cache_dump;
 
    ast_assert(cache != NULL);
    ast_assert(cache->entries != NULL);
 
    cache_dump.eid = eid;
    cache_dump.type = type;
    cache_dump.container = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_NOLOCK, 0, NULL, NULL);
    if (!cache_dump.container) {
        return NULL;
    }
 
    ao2_callback(cache->entries, OBJ_MULTIPLE | OBJ_NODATA, cache_dump_by_eid_cb, &cache_dump);
    return cache_dump.container;
}
 
struct ao2_container *stasis_cache_dump(struct stasis_cache *cache, struct stasis_message_type *type)
{
    return stasis_cache_dump_by_eid(cache, type, &ast_eid_default);
}
 
static int cache_dump_all_cb(void *obj, void *arg, int flags)
{
    struct cache_dump_data *cache_dump = arg;
    struct stasis_cache_entry *entry = obj;
 
    if (!cache_dump->type || entry->key.type == cache_dump->type) {
        if (cache_entry_dump(cache_dump->container, entry)) {
            ao2_cleanup(cache_dump->container);
            cache_dump->container = NULL;
            return CMP_STOP;
        }
    }
 
    return 0;
}
 
struct ao2_container *stasis_cache_dump_all(struct stasis_cache *cache, struct stasis_message_type *type)
{
    struct cache_dump_data cache_dump;
 
    ast_assert(cache != NULL);
    ast_assert(cache->entries != NULL);
 
    cache_dump.eid = NULL;
    cache_dump.type = type;
    cache_dump.container = ao2_container_alloc_list(AO2_ALLOC_OPT_LOCK_NOLOCK, 0, NULL, NULL);
    if (!cache_dump.container) {
        return NULL;
    }
 
    ao2_callback(cache->entries, OBJ_MULTIPLE | OBJ_NODATA, cache_dump_all_cb, &cache_dump);
    return cache_dump.container;
}
 
STASIS_MESSAGE_TYPE_DEFN(stasis_cache_clear_type);
STASIS_MESSAGE_TYPE_DEFN(stasis_cache_update_type);
 
struct stasis_message *stasis_cache_clear_create(struct stasis_message *id_message)
{
    return stasis_message_create(stasis_cache_clear_type(), id_message);
}
 
static void stasis_cache_update_dtor(void *obj)
{
    struct stasis_cache_update *update = obj;
 
    ao2_cleanup(update->old_snapshot);
    update->old_snapshot = NULL;
    ao2_cleanup(update->new_snapshot);
    update->new_snapshot = NULL;
    ao2_cleanup(update->type);
    update->type = NULL;
}
 
static struct stasis_message *update_create(struct stasis_message *old_snapshot, struct stasis_message *new_snapshot)
{
    struct stasis_cache_update *update;
    struct stasis_message *msg;
 
    ast_assert(old_snapshot != NULL || new_snapshot != NULL);
 
    if (!stasis_cache_update_type()) {
        return NULL;
    }
 
    update = ao2_alloc_options(sizeof(*update), stasis_cache_update_dtor,
        AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!update) {
        return NULL;
    }
 
    if (old_snapshot) {
        ao2_ref(old_snapshot, +1);
        update->old_snapshot = old_snapshot;
        if (!new_snapshot) {
            ao2_ref(stasis_message_type(old_snapshot), +1);
            update->type = stasis_message_type(old_snapshot);
        }
    }
    if (new_snapshot) {
        ao2_ref(new_snapshot, +1);
        update->new_snapshot = new_snapshot;
        ao2_ref(stasis_message_type(new_snapshot), +1);
        update->type = stasis_message_type(new_snapshot);
    }
 
    msg = stasis_message_create(stasis_cache_update_type(), update);
 
    ao2_cleanup(update);
    return msg;
}
 
static void caching_topic_exec(void *data, struct stasis_subscription *sub,
    struct stasis_message *message)
{
    struct stasis_caching_topic *caching_topic_needs_unref;
    struct stasis_caching_topic *caching_topic = data;
    struct stasis_message *msg;
    struct stasis_message *msg_put;
    struct stasis_message_type *msg_type;
    const struct ast_eid *msg_eid;
    const char *msg_id;
 
    ast_assert(caching_topic != NULL);
    ast_assert(caching_topic->topic != NULL);
    ast_assert(caching_topic->cache != NULL);
    ast_assert(caching_topic->cache->id_fn != NULL);
 
    if (stasis_subscription_final_message(sub, message)) {
        caching_topic_needs_unref = caching_topic;
    } else {
        caching_topic_needs_unref = NULL;
    }
 
    msg_type = stasis_message_type(message);
 
    if (stasis_subscription_change_type() == msg_type) {
        struct stasis_subscription_change *change = stasis_message_data(message);
 
        /*
         * If this change type is an unsubscribe, we need to find the original
         * subscribe and remove it from the cache otherwise the cache will
         * continue to grow unabated.
         */
        if (strcmp(change->description, "Unsubscribe") == 0) {
            struct stasis_cache_entry *cached_sub;
 
            ao2_wrlock(caching_topic->cache->entries);
            cached_sub = cache_find(caching_topic->cache->entries, stasis_subscription_change_type(), change->uniqueid);
            if (cached_sub) {
                ao2_cleanup(cache_remove(caching_topic->cache->entries, cached_sub, stasis_message_eid(message)));
                ao2_cleanup(cached_sub);
            }
            ao2_unlock(caching_topic->cache->entries);
            ao2_cleanup(caching_topic_needs_unref);
            return;
        }
        msg_put = message;
        msg = message;
    } else if (stasis_cache_clear_type() == msg_type) {
        /* Cache clear event. */
        msg_put = NULL;
        msg = stasis_message_data(message);
        msg_type = stasis_message_type(msg);
    } else {
        /* Normal cache update event. */
        msg_put = message;
        msg = message;
    }
    ast_assert(msg_type != NULL);
 
    msg_eid = stasis_message_eid(msg);/* msg_eid is NULL for aggregate message. */
    msg_id = caching_topic->cache->id_fn(msg);
    if (msg_id && msg_eid) {
        struct stasis_message *update;
        struct cache_put_snapshots snapshots;
 
        /* Update the cache */
        snapshots = cache_put(caching_topic->cache, msg_type, msg_id, msg_eid, msg_put);
        if (snapshots.old || msg_put) {
            if (stasis_topic_subscribers(caching_topic->topic)) {
                update = update_create(snapshots.old, msg_put);
                if (update) {
                    stasis_publish(caching_topic->topic, update);
                    ao2_ref(update, -1);
                }
            }
        } else {
            ast_debug(1,
                "Attempting to remove an item from the %s cache that isn't there: %s %s\n",
                stasis_topic_name(caching_topic->topic),
                stasis_message_type_name(msg_type), msg_id);
        }
 
        if (snapshots.aggregate_old != snapshots.aggregate_new) {
            if (snapshots.aggregate_new && caching_topic->cache->aggregate_publish_fn) {
                caching_topic->cache->aggregate_publish_fn(caching_topic->original_topic,
                    snapshots.aggregate_new);
            }
            if (stasis_topic_subscribers(caching_topic->topic)) {
                update = update_create(snapshots.aggregate_old, snapshots.aggregate_new);
                if (update) {
                    stasis_publish(caching_topic->topic, update);
                    ao2_ref(update, -1);
                }
            }
        }
 
        ao2_cleanup(snapshots.old);
        ao2_cleanup(snapshots.aggregate_old);
        ao2_cleanup(snapshots.aggregate_new);
    }
 
    ao2_cleanup(caching_topic_needs_unref);
}
 
static void print_cache_entry(void *v_obj, void *where, ao2_prnt_fn *prnt)
{
    struct stasis_cache_entry *entry = v_obj;
 
    if (!entry) {
        return;
    }
    prnt(where, "Type: %s  ID: %s  Hash: %u", stasis_message_type_name(entry->key.type),
        entry->key.id, entry->key.hash);
}
 
struct stasis_caching_topic *stasis_caching_topic_create(struct stasis_topic *original_topic, struct stasis_cache *cache)
{
    struct stasis_caching_topic *caching_topic;
    static int caching_id;
    char *new_name;
    int ret;
 
    ret = ast_asprintf(&new_name, "cache:%d/%s", ast_atomic_fetchadd_int(&caching_id, +1), stasis_topic_name(original_topic));
    if (ret < 0) {
        return NULL;
    }
 
    caching_topic = ao2_alloc_options(sizeof(*caching_topic),
        stasis_caching_topic_dtor, AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (caching_topic == NULL) {
        ast_free(new_name);
 
        return NULL;
    }
 
    caching_topic->topic = stasis_topic_create(new_name);
    if (caching_topic->topic == NULL) {
        ao2_ref(caching_topic, -1);
        ast_free(new_name);
 
        return NULL;
    }
 
    ao2_ref(cache, +1);
    caching_topic->cache = cache;
    if (!cache->registered) {
        if (ao2_container_register(new_name, cache->entries, print_cache_entry)) {
            ast_log(LOG_ERROR, "Stasis cache container '%p' for '%s' did not register\n",
                cache->entries, new_name);
        } else {
            cache->registered = 1;
        }
    }
    ast_free(new_name);
 
    caching_topic->sub = internal_stasis_subscribe(original_topic, caching_topic_exec, caching_topic, 0, 0, __FILE__, __LINE__, __PRETTY_FUNCTION__);
    if (caching_topic->sub == NULL) {
        ao2_ref(caching_topic, -1);
 
        return NULL;
    }
 
    ao2_ref(original_topic, +1);
    caching_topic->original_topic = original_topic;
 
    /* The subscription holds the reference, so no additional ref bump. */
    return caching_topic;
}
 
static void stasis_cache_cleanup(void)
{
    STASIS_MESSAGE_TYPE_CLEANUP(stasis_cache_clear_type);
    STASIS_MESSAGE_TYPE_CLEANUP(stasis_cache_update_type);
}
 
int stasis_cache_init(void)
{
    ast_register_cleanup(stasis_cache_cleanup);
 
    if (STASIS_MESSAGE_TYPE_INIT(stasis_cache_clear_type) != 0) {
        return -1;
    }
 
    if (STASIS_MESSAGE_TYPE_INIT(stasis_cache_update_type) != 0) {
        return -1;
    }
 
    return 0;
}