Stasis: address refcount races; implementation comments

Change r395954 reordered some stasis object destruction, which should
have been fine. Unfortunately, it caused some hard to reproduce issues
related to objects being accessed after they had been destroyed. The
patch in r396329 fixed the destruction order problem; this patch
addresses the underlying issue. A few other stasis-related fixes were
also added.

 * Add ref-bumps around areas where objects may get transitively
   destroyed. (For example, where we lock a topic, unref a subscription,
   which unrefs the topic, which explodes the topic when we try to
   unlock it.)

 * Wrote an extensive doxygen page about Stasis implementation,
   relationships between objects, lifecycles of objects, how the
   refcounting works, etc. Many other comments were added, corrected, or
   cleaned up.

 * Added an assert to the topic dtor to catch extra ref decrements.

 * Fixed type used after destruction errors for graceful shutdown in
   stasis_channels.c.

 * I added two unit tests in an attempt to catch destruction order
   issues. Since the underlying cause is a race condition, though, the
   tests rarely failed even when the code was wrong.

 * Fixed a leak in stasis_cache_pattern.c.

(closes issue ASTERISK-22243)
Review: https://reviewboard.asterisk.org/r/2746/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396842 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 95 insertions, 0 deletions

diff --git a/tests/test_stasis.c b/tests/test_stasis.c
index 1e460566b..da9c50874 100644
--- a/tests/test_stasis.c
+++ b/tests/test_stasis.c
@@ -1271,6 +1271,97 @@ AST_TEST_DEFINE(to_ami)
 	return AST_TEST_PASS;
 }
 
+static void noop(void *data, struct stasis_subscription *sub,
+	struct stasis_topic *topic, struct stasis_message *message)
+{
+	/* no-op */
+}
+
+AST_TEST_DEFINE(dtor_order)
+{
+	RAII_VAR(struct stasis_topic *, topic, NULL, ao2_cleanup);
+	RAII_VAR(struct stasis_subscription *, sub, NULL, stasis_unsubscribe);
+
+	switch (cmd) {
+	case TEST_INIT:
+		info->name = __func__;
+		info->category = test_category;
+		info->summary = "Test that destruction order doesn't bomb stuff";
+		info->description = "Test that destruction order doesn't bomb stuff";
+		return AST_TEST_NOT_RUN;
+	case TEST_EXECUTE:
+		break;
+	}
+
+	topic = stasis_topic_create("test-topic");
+	ast_test_validate(test, NULL != topic);
+
+	sub = stasis_subscribe(topic, noop, NULL);
+	ast_test_validate(test, NULL != sub);
+
+	/* With any luck, this won't completely blow everything up */
+	ao2_cleanup(topic);
+	stasis_unsubscribe(sub);
+
+	/* These refs were cleaned up manually */
+	topic = NULL;
+	sub = NULL;
+
+	return AST_TEST_PASS;
+}
+
+static const char *noop_get_id(struct stasis_message *message)
+{
+	return NULL;
+}
+
+AST_TEST_DEFINE(caching_dtor_order)
+{
+	RAII_VAR(struct stasis_topic *, topic, NULL, ao2_cleanup);
+	RAII_VAR(struct stasis_cache *, cache, NULL, ao2_cleanup);
+	RAII_VAR(struct stasis_caching_topic *, caching_topic, NULL,
+		stasis_caching_unsubscribe);
+	RAII_VAR(struct stasis_subscription *, sub, NULL, stasis_unsubscribe);
+
+	switch (cmd) {
+	case TEST_INIT:
+		info->name = __func__;
+		info->category = test_category;
+		info->summary = "Test that destruction order doesn't bomb stuff";
+		info->description = "Test that destruction order doesn't bomb stuff";
+		return AST_TEST_NOT_RUN;
+	case TEST_EXECUTE:
+		break;
+	}
+
+	cache = stasis_cache_create(noop_get_id);
+	ast_test_validate(test, NULL != cache);
+
+	topic = stasis_topic_create("test-topic");
+	ast_test_validate(test, NULL != topic);
+
+	caching_topic = stasis_caching_topic_create(topic, cache);
+	ast_test_validate(test, NULL != caching_topic);
+
+	sub = stasis_subscribe(stasis_caching_get_topic(caching_topic), noop,
+		NULL);
+	ast_test_validate(test, NULL != sub);
+
+	/* With any luck, this won't completely blow everything up */
+	ao2_cleanup(cache);
+	ao2_cleanup(topic);
+	stasis_caching_unsubscribe(caching_topic);
+	stasis_unsubscribe(sub);
+
+	/* These refs were cleaned up manually */
+	cache = NULL;
+	topic = NULL;
+	caching_topic = NULL;
+	sub = NULL;
+
+	return AST_TEST_PASS;
+}
+
 static int unload_module(void)
 {
 	AST_TEST_UNREGISTER(message_type);
@@ -1290,6 +1381,8 @@ static int unload_module(void)
 	AST_TEST_UNREGISTER(to_json);
 	AST_TEST_UNREGISTER(no_to_ami);
 	AST_TEST_UNREGISTER(to_ami);
+	AST_TEST_UNREGISTER(dtor_order);
+	AST_TEST_UNREGISTER(caching_dtor_order);
 	return 0;
 }
 
@@ -1312,6 +1405,8 @@ static int load_module(void)
 	AST_TEST_REGISTER(to_json);
 	AST_TEST_REGISTER(no_to_ami);
 	AST_TEST_REGISTER(to_ami);
+	AST_TEST_REGISTER(dtor_order);
+	AST_TEST_REGISTER(caching_dtor_order);
 	return AST_MODULE_LOAD_SUCCESS;
 }