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, 17 insertions, 4 deletions

diff --git a/main/presencestate.c b/main/presencestate.c
index 45174d5a1..3f394b635 100644
--- a/main/presencestate.c
+++ b/main/presencestate.c
@@ -55,6 +55,7 @@ static const struct {
 
 STASIS_MESSAGE_TYPE_DEFN(ast_presence_state_message_type);
 struct stasis_topic *presence_state_topic_all;
+struct stasis_cache *presence_state_cache;
 struct stasis_caching_topic *presence_state_topic_cached;
 
 /*! \brief  A presence state provider */
@@ -95,7 +96,7 @@ static enum ast_presence_state presence_state_cached(const char *presence_provid
 	RAII_VAR(struct stasis_message *, msg, NULL, ao2_cleanup);
 	struct ast_presence_state_message *presence_state;
 
-	msg = stasis_cache_get(ast_presence_state_topic_cached(), ast_presence_state_message_type(), presence_provider);
+	msg = stasis_cache_get(ast_presence_state_cache(), ast_presence_state_message_type(), presence_provider);
 
 	if (!msg) {
 		return res;
@@ -294,9 +295,14 @@ struct stasis_topic *ast_presence_state_topic_all(void)
 	return presence_state_topic_all;
 }
 
-struct stasis_caching_topic *ast_presence_state_topic_cached(void)
+struct stasis_cache *ast_presence_state_cache(void)
 {
-	return presence_state_topic_cached;
+	return presence_state_cache;
+}
+
+struct stasis_topic *ast_presence_state_topic_cached(void)
+{
+	return stasis_caching_get_topic(presence_state_topic_cached);
 }
 
 static const char *presence_state_get_id(struct stasis_message *msg)
@@ -314,6 +320,8 @@ static void presence_state_engine_cleanup(void)
 {
 	ao2_cleanup(presence_state_topic_all);
 	presence_state_topic_all = NULL;
+	ao2_cleanup(presence_state_cache);
+	presence_state_cache = NULL;
 	presence_state_topic_cached = stasis_caching_unsubscribe_and_join(presence_state_topic_cached);
 	STASIS_MESSAGE_TYPE_CLEANUP(ast_presence_state_message_type);
 }
@@ -331,7 +339,12 @@ int ast_presence_state_engine_init(void)
 		return -1;
 	}
 
-	presence_state_topic_cached = stasis_caching_topic_create(presence_state_topic_all, presence_state_get_id);
+	presence_state_cache = stasis_cache_create(presence_state_get_id);
+	if (!presence_state_cache) {
+		return -1;
+	}
+
+	presence_state_topic_cached = stasis_caching_topic_create(presence_state_topic_all, presence_state_cache);
 	if (!presence_state_topic_cached) {
 		return -1;
 	}