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, 1 insertions, 5 deletions

diff --git a/res/stasis/control.c b/res/stasis/control.c
index 1fbae0c7c..94f1d700d 100644
--- a/res/stasis/control.c
+++ b/res/stasis/control.c
@@ -364,13 +364,9 @@ struct ast_channel_snapshot *stasis_app_control_get_snapshot(
 	const struct stasis_app_control *control)
 {
 	RAII_VAR(struct stasis_message *, msg, NULL, ao2_cleanup);
-	struct stasis_caching_topic *caching_topic;
 	struct ast_channel_snapshot *snapshot;
 
-	caching_topic = ast_channel_topic_all_cached();
-	ast_assert(caching_topic != NULL);
-
-	msg = stasis_cache_get(caching_topic, ast_channel_snapshot_type(),
+	msg = stasis_cache_get(ast_channel_cache(), ast_channel_snapshot_type(),
 		stasis_app_control_get_channel_id(control));
 	if (!msg) {
 		return NULL;