Bug#56822: Add a thread state for sessions waiting on the query cache lock

Only wait for a single debug signal at a time as the signal state
is global. Also, do not activate the query cache debug sync points
if the thread has no associated THD session.

mysql-test/t/query_cache_debug.test:
  Only wait for a single debug signal at a time as the signal state
  is global.
sql/sql_cache.cc:
  Do not execute the debug sync point if the thread has no associated
  THD session. This scenario happens for federated threads.

1 files changed, 11 insertions, 5 deletions

diff --git a/mysql-test/t/query_cache_debug.test b/mysql-test/t/query_cache_debug.test
index 77e714aa6f5..2f85813d1ef 100644
--- a/mysql-test/t/query_cache_debug.test
+++ b/mysql-test/t/query_cache_debug.test
@@ -170,20 +170,26 @@ connection thd2;
 --echo ** On THD2: Insert a result into the cache. This attempt will be blocked
 --echo ** because of a debug hook placed just before the mutex lock after which
 --echo ** the first part of the result set is written.
-SET DEBUG_SYNC="wait_in_query_cache_insert SIGNAL parked2 WAIT_FOR go2";
+SET DEBUG_SYNC="wait_in_query_cache_insert SIGNAL parked2 WAIT_FOR go2 EXECUTE 1";
 --send SELECT SQL_CACHE * FROM t2 UNION SELECT * FROM t3
 
+connection default;
+--echo =================================== Connection default
+--echo ** Assert that the SELECT-stmt thread reaches the sync point.
+SET DEBUG_SYNC="now WAIT_FOR parked2";
+--echo **
+--echo **
+
 connection thd3;
 --echo =================================== Connection thd3
 --echo ** On THD3: Insert another result into the cache and block on the same
 --echo ** debug hook.
-SET DEBUG_SYNC="wait_in_query_cache_insert SIGNAL parked3 WAIT_FOR go3";
---send SELECT SQL_CACHE * FROM t4 UNION SELECT * FROM t5;
+SET DEBUG_SYNC="wait_in_query_cache_insert SIGNAL parked3 WAIT_FOR go3 EXECUTE 1";
+--send SELECT SQL_CACHE * FROM t4 UNION SELECT * FROM t5
 
 connection default;
 --echo =================================== Connection default
---echo ** Assert that the two SELECT-stmt threads to reach the hook.
-SET DEBUG_SYNC="now WAIT_FOR parked2";
+--echo ** Assert that the SELECT-stmt thread reaches the sync point.
 SET DEBUG_SYNC="now WAIT_FOR parked3";
 --echo **
 --echo **