percona_status_wait_query_cache_mutex test is unstable (wrong sync?)

[Laurynas Biveinis]

Here are two example failures from Jenkins builds. The failures show that some threads are observed in different states than was intented by the test, so probably the sync is wrong.

_StringException: Text attachment: traceback
------------
Comment:

Logfile:
CURRENT_TEST: main.percona_status_wait_query_cache_mutex
--- /home/jenkins/workspace/percona-server-5.5-param/BUILD_TYPE/debug/Host/centos6-32/Percona-Server-5.5.16-rel21.0/mysql-test/r/percona_status_wait_query_cache_mutex.result 2011-10-19 16:52:56.047358330 +0300
+++ /home/jenkins/workspace/percona-server-5.5-param/BUILD_TYPE/debug/Host/centos6-32/Percona-Server-5.5.16-rel21.0/mysql-test/r/percona_status_wait_query_cache_mutex.reject 2011-10-19 17:12:18.843730397 +0300
@@ -14,10 +14,10 @@
 SHOW PROCESSLIST;
 Id User Host db Command Time State Info Rows_sent Rows_examined Rows_read
 ### root ### test Query ### NULL SHOW PROCESSLIST ### ### ###
-### root ### test Query ### Waiting on query cache mutex SELECT number from t where id > 0 ### ### ###
+### root ### test Query ### Writing to net SET DEBUG_SYNC='status_waiting_on_query_cache_mutex SIGNAL thread_ready' ### ### ###
 SELECT id, info, state FROM INFORMATION_SCHEMA.PROCESSLIST ORDER BY id;
 id info state
 ### SELECT id, info, state FROM INFORMATION_SCHEMA.PROCESSLIST ORDER BY id executing
-### SELECT number from t where id > 0 Waiting on query cache mutex
+### SET DEBUG_SYNC='status_waiting_on_query_cache_mutex SIGNAL thread_ready' Writing to net
 DROP TABLE t;
 SET GLOBAL query_cache_size=0;

mysqltest: Result length mismatch
------------

_StringException: Text attachment: traceback
------------
Comment:

Logfile:
CURRENT_TEST: main.percona_status_wait_query_cache_mutex
--- /home/jenkins/workspace/percona-server-5.5-param/BUILD_TYPE/debug/Host/centos6-32/Percona-Server-5.5.16-rel21.0/mysql-test/r/percona_status_wait_query_cache_mutex.result 2011-10-19 16:52:56.047358330 +0300
+++ /home/jenkins/workspace/percona-server-5.5-param/BUILD_TYPE/debug/Host/centos6-32/Percona-Server-5.5.16-rel21.0/mysql-test/r/percona_status_wait_query_cache_mutex.reject 2011-10-19 17:12:24.590730118 +0300
@@ -18,6 +18,6 @@
 SELECT id, info, state FROM INFORMATION_SCHEMA.PROCESSLIST ORDER BY id;
 id info state
 ### SELECT id, info, state FROM INFORMATION_SCHEMA.PROCESSLIST ORDER BY id executing
-### SELECT number from t where id > 0 Waiting on query cache mutex
+### NULL
 DROP TABLE t;
 SET GLOBAL query_cache_size=0;

mysqltest: Result length mismatch
------------

http://jenkins.percona.com/view/Percona%20Server%205.5/job/percona-server-5.5-param/168/BUILD_TYPE=debug,Host=centos6-32/testReport/junit/%28root%29/main/percona_status_wait_query_cache_mutex/

http://jenkins.percona.com/view/Percona%20Server%205.5/job/percona-server-5.5-param/168/BUILD_TYPE=debug,Host=centos6-32/testReport/junit/%28root%29/main/percona_status_wait_query_cache_mutex_2/

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-2701