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.

mysql-test/r/create_delayed.result

@@ -0,0 +1,3 @@
+drop table if exists t1;
+Starting test
+# All done

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

sql/mdl.cc

@@ -2078,7 +2078,11 @@ MDL_context::acquire_lock(MDL_request *mdl_request, ulong lock_wait_timeout)
   */
   m_wait.reset_status();
 
-  if (lock->needs_notification(ticket))
+  /*
+    Don't break conflicting locks if timeout is 0 as 0 is used
+    To check if there is any conflicting locks...
+  */
+  if (lock->needs_notification(ticket) && lock_wait_timeout)
     lock->notify_conflicting_locks(this);
 
   mysql_prlock_unlock(&lock->m_rwlock);

sql/sql_base.cc

@@ -9299,7 +9299,11 @@ bool mysql_notify_thread_having_shared_lock(THD *thd, THD *in_use,
     in_use->killed= KILL_SYSTEM_THREAD;
     mysql_mutex_lock(&in_use->mysys_var->mutex);
     if (in_use->mysys_var->current_cond)
+    {
+      mysql_mutex_lock(in_use->mysys_var->current_mutex);
       mysql_cond_broadcast(in_use->mysys_var->current_cond);
+      mysql_mutex_unlock(in_use->mysys_var->current_mutex);
+    }
     mysql_mutex_unlock(&in_use->mysys_var->mutex);
     signalled= TRUE;
   }

sql/sql_insert.cc

@@ -2823,8 +2823,12 @@ pthread_handler_t handle_delayed_insert(void *arg)
         set_timespec(abstime, delayed_insert_timeout);
 
         /* Information for pthread_kill */
+        mysql_mutex_unlock(&di->mutex);
+        mysql_mutex_lock(&di->thd.mysys_var->mutex);
         di->thd.mysys_var->current_mutex= &di->mutex;
         di->thd.mysys_var->current_cond= &di->cond;
+        mysql_mutex_unlock(&di->thd.mysys_var->mutex);
+        mysql_mutex_lock(&di->mutex);
         thd_proc_info(&(di->thd), "Waiting for INSERT");
 
         DBUG_PRINT("info",("Waiting for someone to insert rows"));