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, 189 insertions, 0 deletions

diff --git a/main/stasis_cache_pattern.c b/main/stasis_cache_pattern.c
new file mode 100644
index 000000000..18ae8617e
--- /dev/null
+++ b/main/stasis_cache_pattern.c
@@ -0,0 +1,189 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2013, Digium, Inc.
+ *
+ * David M. Lee, II <dlee@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file
+ *
+ * \brief Typical cache pattern for Stasis topics.
+ *
+ * \author David M. Lee, II <dlee@digium.com>
+ */
+
+/*** MODULEINFO
+	<support_level>core</support_level>
+ ***/
+
+#include "asterisk.h"
+
+ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include "asterisk/astobj2.h"
+#include "asterisk/stasis_cache_pattern.h"
+
+struct stasis_cp_all {
+	struct stasis_topic *topic;
+	struct stasis_topic *topic_cached;
+	struct stasis_cache *cache;
+};
+
+struct stasis_cp_single {
+	struct stasis_topic *topic;
+	struct stasis_caching_topic *topic_cached;
+
+	struct stasis_subscription *forward;
+	struct stasis_subscription *forward_cached;
+};
+
+static void all_dtor(void *obj)
+{
+	struct stasis_cp_all *all = obj;
+
+	ao2_cleanup(all->topic);
+	ao2_cleanup(all->topic_cached);
+	ao2_cleanup(all->cache);
+}
+
+struct stasis_cp_all *stasis_cp_all_create(const char *name,
+	snapshot_get_id id_fn)
+{
+	RAII_VAR(char *, cached_name, NULL, ast_free);
+	RAII_VAR(struct stasis_cp_all *, all, NULL, ao2_cleanup);
+
+	all = ao2_alloc(sizeof(*all), all_dtor);
+	if (!all) {
+		return NULL;
+	}
+
+	ast_asprintf(&cached_name, "%s-cached", name);
+	if (!cached_name) {
+		return NULL;
+	}
+
+	all->topic = stasis_topic_create(name);
+	all->topic_cached = stasis_topic_create(cached_name);
+	all->cache = stasis_cache_create(id_fn);
+
+	if (!all->topic || !all->topic_cached || !all->cache) {
+		return NULL;
+	}
+
+	ao2_ref(all, +1);
+	return all;
+}
+
+struct stasis_topic *stasis_cp_all_topic(struct stasis_cp_all *all)
+{
+	if (!all) {
+		return NULL;
+	}
+	return all->topic;
+}
+
+struct stasis_topic *stasis_cp_all_topic_cached(
+	struct stasis_cp_all *all)
+{
+	if (!all) {
+		return NULL;
+	}
+	return all->topic_cached;
+}
+
+struct stasis_cache *stasis_cp_all_cache(struct stasis_cp_all *all)
+{
+	if (!all) {
+		return NULL;
+	}
+	return all->cache;
+}
+
+static void one_dtor(void *obj)
+{
+	struct stasis_cp_single *one = obj;
+
+	/* Should already be unsubscribed */
+	ast_assert(one->topic_cached == NULL);
+	ast_assert(one->forward == NULL);
+	ast_assert(one->forward_cached == NULL);
+
+	ao2_cleanup(one->topic);
+	one->topic = NULL;
+}
+
+struct stasis_cp_single *stasis_cp_single_create(struct stasis_cp_all *all,
+	const char *name)
+{
+	RAII_VAR(struct stasis_cp_single *, one, NULL, ao2_cleanup);
+
+	one = ao2_alloc(sizeof(*one), one_dtor);
+	if (!one) {
+		return NULL;
+	}
+
+	one->topic = stasis_topic_create(name);
+	if (!one->topic) {
+		return NULL;
+	}
+	one->topic_cached = stasis_caching_topic_create(one->topic, all->cache);
+	if (!one->topic_cached) {
+		return NULL;
+	}
+
+	one->forward = stasis_forward_all(one->topic, all->topic);
+	if (!one->forward) {
+		return NULL;
+	}
+	one->forward_cached = stasis_forward_all(
+		stasis_caching_get_topic(one->topic_cached), all->topic_cached);
+	if (!one->forward_cached) {
+		return NULL;
+	}
+
+	ao2_ref(one, +1);
+	return one;
+}
+
+void stasis_cp_single_unsubscribe(struct stasis_cp_single *one)
+{
+	if (!one) {
+		return;
+	}
+
+	stasis_caching_unsubscribe(one->topic_cached);
+	one->topic_cached = NULL;
+	stasis_unsubscribe(one->forward);
+	one->forward = NULL;
+	stasis_unsubscribe(one->forward_cached);
+	one->forward_cached = NULL;
+}
+
+struct stasis_topic *stasis_cp_single_topic(struct stasis_cp_single *one)
+{
+	if (!one) {
+		return NULL;
+	}
+	return one->topic;
+}
+
+struct stasis_topic *stasis_cp_single_topic_cached(
+	struct stasis_cp_single *one)
+{
+	if (!one) {
+		return NULL;
+	}
+	return stasis_caching_get_topic(one->topic_cached);
+}
+