Implemented MDEV-3941: CREATE TABLE xxx IF NOT EXISTS should not block if table exists.

- Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
- Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.

mysql-test/r/create.result:
  New test case
mysql-test/t/create.test:
  New test case
sql/sql_base.cc:
  Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
  Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.
sql/sql_base.h:
  Updated prototype
sql/sql_db.cc:
  Added extra argument to call to check_if_table_exists()

1 files changed, 21 insertions, 0 deletions

diff --git a/mysql-test/t/create.test b/mysql-test/t/create.test
index d80127df860..c472c9f0a05 100644
--- a/mysql-test/t/create.test
+++ b/mysql-test/t/create.test
@@ -1996,4 +1996,25 @@ create table if not exists t1 (a int unique, b int)
   ignore select 1 as a, 1 as b union select 1 as a, 2 as b;
 select * from t1;
 drop table t1;
+
+--echo #
+--echo # Checking that CREATE IF NOT EXISTS is not blocked by running SELECT
 --echo #
+
+create table t1 (a int, b int) engine=myisam;
+create table t2 (a int, b int) engine=myisam;
+insert into t1 values (1,1);
+lock tables t1 read;
+connect (user1,localhost,root,,test);
+set @@lock_wait_timeout=5;
+--error ER_TABLE_EXISTS_ERROR
+create table if not exists t1 (a int, b int);
+--error ER_TABLE_EXISTS_ERROR
+create table if not exists t1 (a int, b int) select 2,2;
+--error ER_TABLE_EXISTS_ERROR
+create table if not exists t1 like t2;
+disconnect user1;
+connection default;
+select * from t1;
+unlock tables;
+drop table t1,t2;