Split caching out from the stasis_caching_topic.

In working with res_stasis, I discovered a significant limitation to
the current structure of stasis_caching_topics: you cannot subscribe
to cache updates for a single channel/bridge/endpoint/etc.

To address this, this patch splits the cache away from the
stasis_caching_topic, making it a first class object. The stasis_cache
object is shared amongst individual stasis_caching_topics that are
created per channel/endpoint/etc. These are still forwarded to global
whatever_all_cached topics, so their use from most of the code does
not change.

In making these changes, I noticed that we frequently used a similar
pattern for bridges, endpoints and channels:

     single_topic  ---------------->  all_topic
           ^
           |
     single_topic_cached  ----+---->  all_topic_cached
                              |
                              +---->  cache

This pattern was extracted as the 'Stasis Caching Pattern', defined in
stasis_caching_pattern.h. This avoids a lot of duplicate code between
the different domain objects.

Since the cache is now disassociated from its upstream caching topics,
this also necessitated a change to how the 'guaranteed' flag worked
for retrieving from a cache. The code for handling the caching
guarantee was extracted into a 'stasis_topic_wait' function, which
works for any stasis_topic.

(closes issue ASTERISK-22002)
Review: https://reviewboard.asterisk.org/r/2672/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@395954 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 153 insertions, 0 deletions

diff --git a/include/asterisk/stasis_cache_pattern.h b/include/asterisk/stasis_cache_pattern.h
new file mode 100644
index 000000000..2ea643e19
--- /dev/null
+++ b/include/asterisk/stasis_cache_pattern.h
@@ -0,0 +1,153 @@
+/*
+ * 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.
+ */
+
+#ifndef _ASTERISK_STASIS_CACHE_PATTERN_H
+#define _ASTERISK_STASIS_CACHE_PATTERN_H
+
+/*! \file
+ *
+ * \brief Caching pattern for \ref stasis topics.
+ *
+ * A typical pattern for Stasis objects is to have individual objects, which
+ * have their own topic and caching topic. These individual topics feed an
+ * upstream aggregate topics, and a shared cache.
+ *
+ * The \ref stasis_cp_all object contains the aggregate topics and shared cache.
+ * This is built with the base name for the topics, and the identity function to
+ * identify messages in the cache.
+ *
+ * The \ref stasis_cp_single object contains the \ref stasis_topic for a single
+ * instance, and the corresponding \ref stasis_caching_topic.
+ *
+ * Since the \ref stasis_cp_single object has subscriptions for forwarding
+ * and caching, it must be disposed of using stasis_cp_single_unsubscribe()
+ * instead of simply ao2_cleanup().
+ */
+
+#include "asterisk/stasis.h"
+
+/*!
+ * \brief The 'all' side of the cache pattern. These are typically built as
+ * global objects for specific modules.
+ */
+struct stasis_cp_all;
+
+/*!
+ * \brief Create an all instance of the cache pattern.
+ *
+ * This object is AO2 managed, so dispose of it with ao2_cleanup().
+ *
+ * \param name Base name of the topics.
+ * \param id_fn Identity function for the cache.
+ * \return All side instance.
+ * \return \c NULL on error.
+ */
+struct stasis_cp_all *stasis_cp_all_create(const char *name,
+	snapshot_get_id id_fn);
+
+/*!
+ * \brief Get the aggregate topic.
+ *
+ * This topic aggregates all messages published to corresponding
+ * stasis_cp_single_topic() topics.
+ *
+ * \param all All side caching pattern object.
+ * \return The aggregate topic.
+ * \return \c NULL if \a all is \c NULL
+ */
+struct stasis_topic *stasis_cp_all_topic(struct stasis_cp_all *all);
+
+/*!
+ * \brief Get the caching topic.
+ *
+ * This topic aggregates all messages from the corresponding
+ * stasis_cp_single_topic_cached() topics.
+ *
+ * Note that one normally only subscribes to the caching topic, since data
+ * is fed to it from its upstream topic.
+ *
+ * \param all All side caching pattern object.
+ * \return The aggregate caching topic.
+ * \return \c NULL if \a all is \c NULL
+ */
+struct stasis_topic *stasis_cp_all_topic_cached(
+	struct stasis_cp_all *all);
+
+/*!
+ * \brief Get the cache.
+ *
+ * This is the shared cache for all corresponding \ref stasis_cp_single objects.
+ *
+ * \param all All side caching pattern object.
+ * \return The cache.
+ * \return \c NULL if \a all is \c NULL
+ */
+struct stasis_cache *stasis_cp_all_cache(struct stasis_cp_all *all);
+
+/*!
+ * \brief The 'one' side of the cache pattern. These are built per-instance for
+ * some corresponding object, and must be explicitly disposed of using
+ * stasis_cp_single_unsubscribe().
+ */
+struct stasis_cp_single;
+
+/*!
+ * \brief Create the 'one' side of the cache pattern.
+ *
+ * Dispose of using stasis_cp_single_unsubscribe().
+ *
+ * \param all Corresponding all side.
+ * \param name Base name for the topics.
+ * \return One side instance
+ */
+struct stasis_cp_single *stasis_cp_single_create(struct stasis_cp_all *all,
+	const char *name);
+
+/*!
+ * \brief Stops caching and forwarding messages.
+ *
+ * \param one One side of the cache pattern.
+ */
+void stasis_cp_single_unsubscribe(struct stasis_cp_single *one);
+
+/*!
+ * \brief Get the topic for this instance.
+ *
+ * This is the topic to which one would post instance-specific messages, or
+ * subscribe for single-instance, uncached messages.
+ *
+ * \param one One side of the cache pattern.
+ * \return The main topic.
+ * \return \c NULL if \a one is \c NULL
+ */
+struct stasis_topic *stasis_cp_single_topic(struct stasis_cp_single *one);
+
+/*!
+ * \brief Get the caching topic for this instance.
+ *
+ * Note that one normally only subscribes to the caching topic, since data
+ * is fed to it from its upstream topic.
+ *
+ * \param one One side of the cache pattern.
+ * \return The caching topic.
+ * \return \c NULL if \a one is \c NULL
+ */
+struct stasis_topic *stasis_cp_single_topic_cached(
+	struct stasis_cp_single *one);
+
+#endif /* _ASTERISK_STASIS_CACHE_PATTERN_H */