Bug#37481: status.test fails randomly

The problem was that the test was trying to obtain a lock on
a table in one connection without ensuring that a insert which
was executed in another connection had released the lock on the
same table.

The solution is to add a dummy select query after the insert to
ensure that the table is unlocked and closed by the time it tries
to lock it again. This is enough to prevent test failures described
in the bug report. As an extra safety measure, concurrent inserts
are disabled.

Remove comments that calculated the Table_locks_immediate. This
value is not tested anymore and it's calculation did not reflect
the actual value.

mysql-test/r/status.result

+set @old_concurrent_insert= @@global.concurrent_insert;
+set @@global.concurrent_insert= 0;
 flush status;
 show status like 'Table_lock%';
 Variable_name	Value
@@ -7,22 +9,31 @@ select * from information_schema.session_status where variable_name like 'Table_
 VARIABLE_NAME	VARIABLE_VALUE
 TABLE_LOCKS_IMMEDIATE	2
 TABLE_LOCKS_WAITED	0
-SET SQL_LOG_BIN=0;
+# Switched to connection: con1
+set sql_log_bin=0;
 set @old_general_log = @@global.general_log;
 set global general_log = 'OFF';
 drop table if exists t1;
 create table t1(n int) engine=myisam;
 insert into t1 values(1);
+select 1;
+1
+1
+# Switched to connection: con2
 lock tables t1 read;
 unlock tables;
 lock tables t1 read;
+# Switched to connection: con1
 update t1 set n = 3;
+# Switched to connection: con2
 unlock tables;
+# Switched to connection: con1
 show status like 'Table_locks_waited';
 Variable_name	Value
 Table_locks_waited	1
 drop table t1;
 set global general_log = @old_general_log;
+# Switched to connection: default
 select 1;
 1
 1
@@ -198,3 +209,4 @@ ERROR 42000: SELECT command denied to user 'mysqltest_1'@'localhost' for table '
 drop database db37908;
 drop procedure proc37908;
 drop function func37908;
+set @@global.concurrent_insert= @old_concurrent_insert;

mysql-test/t/status.test

@@ -4,6 +4,11 @@
 # embedded server causes different stat
 -- source include/not_embedded.inc
 
+# Disable concurrent inserts to avoid sporadic test failures as it might
+# affect the the value of variables used throughout the test case.
+set @old_concurrent_insert= @@global.concurrent_insert;
+set @@global.concurrent_insert= 0;
+
 # PS causes different statistics
 --disable_ps_protocol
 
@@ -12,54 +17,45 @@ connect (con2,localhost,root,,);
 
 flush status;
 
-# Logging to the general query log table (--log-output=table --log) increments
-# Table_locks_immediate with each query, so here Immediate becomes 1
 show status like 'Table_lock%';
-# ++Immediate = 2
 select * from information_schema.session_status where variable_name like 'Table_lock%';
 
 connection con1;
-# ++Immediate = 3
-SET SQL_LOG_BIN=0;
-set @old_general_log = @@global.general_log;                                      
+--echo # Switched to connection: con1
+set sql_log_bin=0;
+set @old_general_log = @@global.general_log;
 set global general_log = 'OFF';
 --disable_warnings
-# ++Immediate = 4
 drop table if exists t1;
 --enable_warnings
 
-# ++Immediate = 5
 create table t1(n int) engine=myisam;
-# Immediate + 2 = 7
 insert into t1 values(1);
+# Execute dummy select in order to ensure that tables used in the
+# previous statement are unlocked and closed.
+select 1;
 
 connection con2;
-# Immediate + 2 = 9
+--echo # Switched to connection: con2
 lock tables t1 read;
-# ++Immediate = 10
 unlock tables;
-# Immediate + 2 = 12
 lock tables t1 read;
 
 connection con1;
-# ++Immediate = 13
+--echo # Switched to connection: con1
 let $ID= `select connection_id()`;
-# ++Immediate = 14 (Not +2, because this increments Table_locks_waited)
---send
-update t1 set n = 3;
+--send update t1 set n = 3
 
 connection con2;
+--echo # Switched to connection: con2
 # wait for the other query to start executing
 let $wait_condition= select 1 from INFORMATION_SCHEMA.PROCESSLIST where ID = $ID and STATE = "Locked";
-# Immediate = 14 + $wait_condition_reps ($wait_timeout is 0, so no extra select
-# is done inside wait_condition.inc)
 --source include/wait_condition.inc
-# ++Immediate = 15 + $wait_condition_reps
 unlock tables;
 
 connection con1;
+--echo # Switched to connection: con1
 reap;
-# ++Immediate = 16 + $wait_condition_reps
 show status like 'Table_locks_waited';
 drop table t1;
 set global general_log = @old_general_log;
@@ -67,6 +63,7 @@ set global general_log = @old_general_log;
 disconnect con2;
 disconnect con1;
 connection default;
+--echo # Switched to connection: default
 
 # End of 4.1 tests
 
@@ -295,3 +292,7 @@ drop database db37908;
 drop procedure proc37908;
 drop function func37908;
 # End of 5.1 tests
+
+# Restore global concurrent_insert value. Keep in the end of the test file.
+--connection default
+set @@global.concurrent_insert= @old_concurrent_insert;