Patch that refactors global read lock implementation and fixes

bug #57006 "Deadlock between HANDLER and FLUSH TABLES WITH READ
LOCK" and bug #54673 "It takes too long to get readlock for
'FLUSH TABLES WITH READ LOCK'".

The first bug manifested itself as a deadlock which occurred
when a connection, which had some table open through HANDLER
statement, tried to update some data through DML statement
while another connection tried to execute FLUSH TABLES WITH
READ LOCK concurrently.

What happened was that FTWRL in the second connection managed
to perform first step of GRL acquisition and thus blocked all
upcoming DML. After that it started to wait for table open
through HANDLER statement to be flushed. When the first connection
tried to execute DML it has started to wait for GRL/the second
connection creating deadlock.

The second bug manifested itself as starvation of FLUSH TABLES
WITH READ LOCK statements in cases when there was a constant
stream of concurrent DML statements (in two or more
connections).

This has happened because requests for protection against GRL
which were acquired by DML statements were ignoring presence of
pending GRL and thus the latter was starved.

This patch solves both these problems by re-implementing GRL
using metadata locks.

Similar to the old implementation acquisition of GRL in new
implementation is two-step. During the first step we block
all concurrent DML and DDL statements by acquiring global S
metadata lock (each DML and DDL statement acquires global IX
lock for its duration). During the second step we block commits
by acquiring global S lock in COMMIT namespace (commit code
acquires global IX lock in this namespace).

Note that unlike in old implementation acquisition of
protection against GRL in DML and DDL is semi-automatic.
We assume that any statement which should be blocked by GRL
will either open and acquires write-lock on tables or acquires
metadata locks on objects it is going to modify. For any such
statement global IX metadata lock is automatically acquired
for its duration.

The first problem is solved because waits for GRL become
visible to deadlock detector in metadata locking subsystem
and thus deadlocks like one in the first bug become impossible.

The second problem is solved because global S locks which
are used for GRL implementation are given preference over
IX locks which are acquired by concurrent DML (and we can
switch to fair scheduling in future if needed).

Important change:
FTWRL/GRL no longer blocks DML and DDL on temporary tables.
Before this patch behavior was not consistent in this respect:
in some cases DML/DDL statements on temporary tables were
blocked while in others they were not. Since the main use cases
for FTWRL are various forms of backups and temporary tables are
not preserved during backups we have opted for consistently
allowing DML/DDL on temporary tables during FTWRL/GRL.

Important change:
This patch changes thread state names which are used when
DML/DDL of FTWRL is waiting for global read lock. It is now
either "Waiting for global read lock" or "Waiting for commit
lock" depending on the stage on which FTWRL is.

Incompatible change:
To solve deadlock in events code which was exposed by this
patch we have to replace LOCK_event_metadata mutex with
metadata locks on events. As result we have to prohibit
DDL on events under LOCK TABLES.

This patch also adds extensive test coverage for interaction
of DML/DDL and FTWRL.

Performance of new and old global read lock implementations
in sysbench tests were compared. There were no significant
difference between new and old implementations.

mysql-test/t/lock_multi.test

@@ -228,7 +228,7 @@ connection writer;
 # Sleep a bit till the flush of connection locker is in work and hangs
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock" and
+  where state = "Waiting for global read lock" and
         info = "FLUSH TABLES WITH READ LOCK";
 --source include/wait_condition.inc
 # This must not block.
@@ -260,7 +260,7 @@ connection writer;
 # Sleep a bit till the flush of connection locker is in work and hangs
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock" and
+  where state = "Waiting for global read lock" and
         info = "FLUSH TABLES WITH READ LOCK";
 --source include/wait_condition.inc
 --error ER_TABLE_NOT_LOCKED
@@ -296,10 +296,11 @@ DROP DATABASE mysqltest_1;
 # With bug in place: try to acquire LOCK_mysql_create_table...
 # When fixed: Reject dropping db because of the read lock.
 connection con1;
-# Wait a bit so that the session con2 is in state "Waiting for release of readlock"
+# Wait a bit so that the session con2 is in state
+# "Waiting for global read lock"
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for release of readlock"
+  where state = "Waiting for global read lock"
   and info = "DROP DATABASE mysqltest_1";
 --source include/wait_condition.inc
 --error ER_CANT_UPDATE_WITH_READLOCK
@@ -376,7 +377,7 @@ connection con5;
 --echo # con5
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock" and
+  where state = "Waiting for global read lock" and
         info = "flush tables with read lock";
 --source include/wait_condition.inc
 --echo # global read lock is taken
@@ -384,10 +385,11 @@ connection con3;
 --echo # con3
 send select * from t2 for update;
 connection con5;
-let $show_statement= SHOW PROCESSLIST;
-let $field= State;
-let $condition= = 'Waiting for release of readlock';
---source include/wait_show_condition.inc
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Waiting for global read lock" and
+        info = "select * from t2 for update";
+--source include/wait_condition.inc
 --echo # waiting for release of read lock
 connection con4;
 --echo # con4
@@ -433,10 +435,11 @@ connection con1;
 send update t2 set a = 1;
 connection default;
 --echo # default
-let $show_statement= SHOW PROCESSLIST;
-let $field= State;
-let $condition= = 'Waiting for release of readlock';
---source include/wait_show_condition.inc
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Waiting for global read lock" and
+        info = "update t2 set a = 1";
+--source include/wait_condition.inc
 --echo # statement is waiting for release of read lock
 connection con2;
 --echo # con2
@@ -460,10 +463,11 @@ connection con1;
 send lock tables t2 write;
 connection default;
 --echo # default
-let $show_statement= SHOW PROCESSLIST;
-let $field= State;
-let $condition= = 'Waiting for release of readlock';
---source include/wait_show_condition.inc
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Waiting for global read lock" and
+        info = "lock tables t2 write";
+--source include/wait_condition.inc
 --echo # statement is waiting for release of read lock
 connection con2;
 --echo # con2
@@ -571,7 +575,8 @@ connection default;
 --echo connection: default
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock" and
+        info = "flush tables with read lock";
 --source include/wait_condition.inc
 alter table t1 add column j int;
 connect (insert,localhost,root,,test,,);
@@ -579,14 +584,16 @@ connection insert;
 --echo connection: insert
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock" and
+        info = "flush tables with read lock";
 --source include/wait_condition.inc
 --send insert into t1 values (1,2);
 --echo connection: default
 connection default;
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for release of readlock";
+  where state = "Waiting for global read lock" and
+        info = "insert into t1 values (1,2)";
 --source include/wait_condition.inc
 unlock tables;
 connection flush;
@@ -594,7 +601,8 @@ connection flush;
 --reap
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for release of readlock";
+  where state = "Waiting for global read lock" and
+        info = "insert into t1 values (1,2)";
 --source include/wait_condition.inc
 select * from t1;
 unlock tables;
@@ -629,12 +637,12 @@ connection default;
 --echo connection: default
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock";
 --source include/wait_condition.inc
 flush tables;
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock";
 --source include/wait_condition.inc
 unlock tables;
 connection flush;
@@ -698,12 +706,12 @@ connection default;
 --echo connection: default
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock";
 --source include/wait_condition.inc
 flush tables;
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
-  where state = "Waiting for global metadata lock";
+  where state = "Waiting for global read lock";
 --source include/wait_condition.inc
 drop table t1;
 connection flush;