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, 19 insertions, 7 deletions

diff --git a/main/devicestate.c b/main/devicestate.c
index b2c70f764..c16a0628b 100644
--- a/main/devicestate.c
+++ b/main/devicestate.c
@@ -196,6 +196,7 @@ static ast_cond_t change_pending;
 struct stasis_subscription *devstate_message_sub;
 
 static struct stasis_topic *device_state_topic_all;
+static struct stasis_cache *device_state_cache;
 static struct stasis_caching_topic *device_state_topic_cached;
 static struct stasis_topic_pool *device_state_topic_pool;
 
@@ -285,7 +286,7 @@ static enum ast_device_state devstate_cached(const char *device)
 	RAII_VAR(struct stasis_message *, cached_msg, NULL, ao2_cleanup);
 	struct ast_device_state_message *device_state;
 
-	cached_msg = stasis_cache_get(ast_device_state_topic_cached(), ast_device_state_message_type(), device);
+	cached_msg = stasis_cache_get(ast_device_state_cache(), ast_device_state_message_type(), device);
 	if (!cached_msg) {
 		return AST_DEVICE_UNKNOWN;
 	}
@@ -586,7 +587,7 @@ static enum ast_device_state get_aggregate_state(char *device)
 
 	ast_devstate_aggregate_init(&aggregate);
 
-	cached = stasis_cache_dump(ast_device_state_topic_cached(), NULL);
+	cached = stasis_cache_dump(ast_device_state_cache(), NULL);
 
 	ao2_callback_data(cached, OBJ_NODATA, devstate_change_aggregator_cb, &aggregate, device);
 
@@ -598,7 +599,7 @@ static int aggregate_state_changed(char *device, enum ast_device_state new_aggre
 	RAII_VAR(struct stasis_message *, cached_aggregate_msg, NULL, ao2_cleanup);
 	struct ast_device_state_message *cached_aggregate_device_state;
 
-	cached_aggregate_msg = stasis_cache_get(ast_device_state_topic_cached(), ast_device_state_message_type(), device);
+	cached_aggregate_msg = stasis_cache_get(ast_device_state_cache(), ast_device_state_message_type(), device);
 	if (!cached_aggregate_msg) {
 		return 1;
 	}
@@ -719,9 +720,14 @@ struct stasis_topic *ast_device_state_topic_all(void)
 	return device_state_topic_all;
 }
 
-struct stasis_caching_topic *ast_device_state_topic_cached(void)
+struct stasis_cache *ast_device_state_cache(void)
 {
-	return device_state_topic_cached;
+	return device_state_cache;
+}
+
+struct stasis_topic *ast_device_state_topic_cached(void)
+{
+	return stasis_caching_get_topic(device_state_topic_cached);
 }
 
 struct stasis_topic *ast_device_state_topic(const char *device)
@@ -777,6 +783,8 @@ static void devstate_cleanup(void)
 	devstate_message_sub = stasis_unsubscribe_and_join(devstate_message_sub);
 	ao2_cleanup(device_state_topic_all);
 	device_state_topic_all = NULL;
+	ao2_cleanup(device_state_cache);
+	device_state_cache = NULL;
 	device_state_topic_cached = stasis_caching_unsubscribe_and_join(device_state_topic_cached);
 	STASIS_MESSAGE_TYPE_CLEANUP(ast_device_state_message_type);
 	ao2_cleanup(device_state_topic_pool);
@@ -794,7 +802,11 @@ int devstate_init(void)
 	if (!device_state_topic_all) {
 		return -1;
 	}
-	device_state_topic_cached = stasis_caching_topic_create(device_state_topic_all, device_state_get_id);
+	device_state_cache = stasis_cache_create(device_state_get_id);
+	if (!device_state_cache) {
+		return -1;
+	}
+	device_state_topic_cached = stasis_caching_topic_create(device_state_topic_all, device_state_cache);
 	if (!device_state_topic_cached) {
 		return -1;
 	}
@@ -803,7 +815,7 @@ int devstate_init(void)
 		return -1;
 	}
 
-	devstate_message_sub = stasis_subscribe(stasis_caching_get_topic(ast_device_state_topic_cached()), devstate_change_collector_cb, NULL);
+	devstate_message_sub = stasis_subscribe(ast_device_state_topic_cached(), devstate_change_collector_cb, NULL);
 
 	if (!devstate_message_sub) {
 		ast_log(LOG_ERROR, "Failed to create subscription for the device state change collector\n");