Fix for MDEV-4009: main.delayed sporadically fails with "query 'REPLACE DELAYED t1 VALUES (5)' failed: 1317: Query execution was interrupted"

- Fixed broadcast without a proper mutex
- Don't break existing locks if we are just testing if we can get the lock

mysql-test/r/create_delayed.result:
  Added test case for failures with INSERT DELAYED with CREATE and DROP TABLE
mysql-test/t/create_delayed.test:
  Added test case for failures with INSERT DELAYED with CREATE and DROP TABLE
sql/mdl.cc:
  Don't break existing locks for timeout=0 (ie, just check if there are conflicting locks).
  This fixed the bug that INSERT DELAYED didn't work properly with CREATE TABLE
sql/sql_base.cc:
  One neads to hold the mutex before doing a mysql_cond_broadcast()
  This fixed the bug that INSERT DELAYED didn't work properly with DROP TABLE
sql/sql_insert.cc:
  Protect setting of mysys_var->current_mutex.

1 files changed, 34 insertions, 0 deletions

diff --git a/mysql-test/t/create_delayed.test b/mysql-test/t/create_delayed.test
new file mode 100644
index 00000000000..e99886d97d1
--- /dev/null
+++ b/mysql-test/t/create_delayed.test
@@ -0,0 +1,34 @@
+#
+# Ensure that INSERT DELAYED works with CREATE TABLE on existing table
+#
+
+-- source include/big_test.inc
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+
+--disable_query_log
+--disable_result_log
+
+--let $run=1000
+
+--echo Starting test
+
+while ($run)
+{
+# --echo # $run attempts left...
+  CREATE TABLE t1 ( f1 INTEGER AUTO_INCREMENT, PRIMARY KEY (f1)) ENGINE=MyISAM;
+  INSERT DELAYED t1 VALUES (4);
+--error ER_TABLE_EXISTS_ERROR
+  CREATE TABLE t1 AS SELECT 1 AS f1;
+
+  REPLACE DELAYED t1 VALUES (5);
+  DROP TABLE t1;
+--dec $run
+}
+
+--enable_query_log
+--enable_result_log
+
+--echo # All done