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, 34 insertions, 1 deletions

diff --git a/include/asterisk/stasis_endpoints.h b/include/asterisk/stasis_endpoints.h
index 6d7f8dbaa..4a35e9587 100644
--- a/include/asterisk/stasis_endpoints.h
+++ b/include/asterisk/stasis_endpoints.h
@@ -30,6 +30,7 @@
 #include "asterisk/endpoints.h"
 #include "asterisk/json.h"
 #include "asterisk/stasis.h"
+#include "asterisk/stasis_cache_pattern.h"
 #include "asterisk/stringfields.h"
 
 /*! \addtogroup StasisTopicsAndMessages
@@ -144,6 +145,31 @@ struct ast_endpoint_snapshot *ast_endpoint_snapshot_create(
 struct stasis_topic *ast_endpoint_topic(struct ast_endpoint *endpoint);
 
 /*!
+ * \brief Returns the topic for a specific endpoint.
+ *
+ * \ref ast_endpoint_snapshot messages are replaced with
+ * \ref stasis_cache_update
+ *
+ * \param endpoint The endpoint.
+ * \return The topic for the given endpoint.
+ * \return ast_endpoint_topic_all() if endpoint is \c NULL.
+ * \since 12
+ */
+struct stasis_topic *ast_endpoint_topic_cached(struct ast_endpoint *endpoint);
+
+/*!
+ * \internal
+ * \brief Cache and global topics for endpoints.
+ *
+ * This is public simply to be used by endpoints.c. Please use the accessor
+ * functions (ast_endpoint_topic_all(), ast_endpoint_topic_all_cached(),
+ * ast_endpoint_cache(), etc.) instead of calling this directly.
+ *
+ * \since 12
+ */
+struct stasis_cp_all *ast_endpoint_cache_all(void);
+
+/*!
  * \brief Topic for all endpoint releated messages.
  * \since 12
  */
@@ -153,7 +179,14 @@ struct stasis_topic *ast_endpoint_topic_all(void);
  * \brief Cached topic for all endpoint related messages.
  * \since 12
  */
-struct stasis_caching_topic *ast_endpoint_topic_all_cached(void);
+struct stasis_topic *ast_endpoint_topic_all_cached(void);
+
+/*!
+ * \brief Backend cache for ast_endpoint_topic_all_cached().
+ * \return Cache of \ref ast_endpoint_snapshot.
+ * \since 12
+ */
+struct stasis_cache *ast_endpoint_cache(void);
 
 /*!
  * \brief Retrieve the most recent snapshot for the endpoint with the given