WL#3984 (Revise locking of mysql.general_log and mysql.slow_log)

Bug#25422 (Hang with log tables)
Bug 17876 (Truncating mysql.slow_log in a SP after using cursor locks the
          thread)
Bug 23044 (Warnings on flush of a log table)
Bug 29129 (Resetting general_log while the GLOBAL READ LOCK is set causes
           a deadlock)

Prior to this fix, the server would hang when performing concurrent
ALTER TABLE or TRUNCATE TABLE statements against the LOG TABLES,
which are mysql.general_log and mysql.slow_log.

The root cause traces to the following code:
in sql_base.cc, open_table()
  if (table->in_use != thd)
  {
    /* wait_for_condition will unlock LOCK_open for us */
    wait_for_condition(thd, &LOCK_open, &COND_refresh);
  }
The problem with this code is that the current implementation of the
LOGGER creates 'fake' THD objects, like
- Log_to_csv_event_handler::general_log_thd
- Log_to_csv_event_handler::slow_log_thd
which are not associated to a real thread running in the server,
so that waiting for these non-existing threads to release table locks
cause the dead lock.

In general, the design of Log_to_csv_event_handler does not fit into the
general architecture of the server, so that the concept of general_log_thd
and slow_log_thd has to be abandoned:
- this implementation does not work with table locking
- it will not work with commands like SHOW PROCESSLIST
- having the log tables always opened does not integrate well with DDL
operations / FLUSH TABLES / SET GLOBAL READ_ONLY

With this patch, the fundamental design of the LOGGER has been changed to:
- always open and close a log table when writing a log
- remove totally the usage of fake THD objects
- clarify how locking of log tables is implemented in general.

See WL#3984 for details related to the new locking design.

Additional changes (misc bugs exposed and fixed):

1)

mysqldump which would ignore some tables in dump_all_tables_in_db(),
 but forget to ignore the same in dump_all_views_in_db().

2)

mysqldump would also issue an empty "LOCK TABLE" command when all the tables
to lock are to be ignored (numrows == 0), instead of not issuing the query.

3)

Internal errors handlers could intercept errors but not warnings
(see sql_error.cc).

4)

Implementing a nested call to open tables, for the performance schema tables,
exposed an existing bug in remove_table_from_cache(), which would perform:
  in_use->some_tables_deleted=1;
against another thread, without any consideration about thread locking.
This call inside remove_table_from_cache() was not required anyway,
since calling mysql_lock_abort() takes care of aborting -- cleanly -- threads
that might hold a lock on a table.
This line (in_use->some_tables_deleted=1) has been removed.

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/sql_udf.cc b/sql/sql_udf.cc
index 8361fc64f33..10bb7844d88 100644
--- a/sql/sql_udf.cc
+++ b/sql/sql_udf.cc
@@ -472,7 +472,7 @@ int mysql_create_function(THD *thd,udf_func *udf)
   tables.db= (char*) "mysql";
   tables.table_name= tables.alias= (char*) "func";
   /* Allow creation of functions even if we can't open func table */
-  if (!(table = open_ltable(thd,&tables,TL_WRITE)))
+  if (!(table = open_ltable(thd, &tables, TL_WRITE, 0)))
     goto err;
   table->use_all_columns();
   restore_record(table, s->default_values);	// Default values for fields
@@ -547,7 +547,7 @@ int mysql_drop_function(THD *thd,const LEX_STRING *udf_name)
   bzero((char*) &tables,sizeof(tables));
   tables.db=(char*) "mysql";
   tables.table_name= tables.alias= (char*) "func";
-  if (!(table = open_ltable(thd,&tables,TL_WRITE)))
+  if (!(table = open_ltable(thd, &tables, TL_WRITE, 0)))
     goto err;
   table->use_all_columns();
   table->field[0]->store(exact_name_str, exact_name_len, &my_charset_bin);