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, 14 insertions, 4 deletions

diff --git a/main/app.c b/main/app.c
index 031f6f28f..8d081fe8c 100644
--- a/main/app.c
+++ b/main/app.c
@@ -88,6 +88,7 @@ static AST_LIST_HEAD_STATIC(zombies, zombie);
  * @{ \brief Define \ref stasis topic objects for MWI
  */
 static struct stasis_topic *mwi_topic_all;
+static struct stasis_cache *mwi_state_cache;
 static struct stasis_caching_topic *mwi_topic_cached;
 static struct stasis_topic_pool *mwi_topic_pool;
 /* @} */
@@ -2696,9 +2697,14 @@ struct stasis_topic *ast_mwi_topic_all(void)
 	return mwi_topic_all;
 }
 
-struct stasis_caching_topic *ast_mwi_topic_cached(void)
+struct stasis_cache *ast_mwi_state_cache(void)
 {
-	return mwi_topic_cached;
+	return mwi_state_cache;
+}
+
+struct stasis_topic *ast_mwi_topic_cached(void)
+{
+	return stasis_caching_get_topic(mwi_topic_cached);
 }
 
 struct stasis_topic *ast_mwi_topic(const char *uniqueid)
@@ -2754,7 +2760,7 @@ int ast_publish_mwi_state_full(
 
 	if (!ast_strlen_zero(channel_id)) {
 		RAII_VAR(struct stasis_message *, chan_message,
-			stasis_cache_get(ast_channel_topic_all_cached(),
+			stasis_cache_get(ast_channel_cache(),
 					ast_channel_snapshot_type(),
 					channel_id),
 			ao2_cleanup);
@@ -2855,7 +2861,11 @@ int app_init(void)
 	if (!mwi_topic_all) {
 		return -1;
 	}
-	mwi_topic_cached = stasis_caching_topic_create(mwi_topic_all, mwi_state_get_id);
+	mwi_state_cache = stasis_cache_create(mwi_state_get_id);
+	if (!mwi_state_cache) {
+		return -1;
+	}
+	mwi_topic_cached = stasis_caching_topic_create(mwi_topic_all, mwi_state_cache);
 	if (!mwi_topic_cached) {
 		return -1;
 	}