Bug#47525: MySQL crashed (Federated)

On Mac OS X or Windows, sending a SIGHUP to the server or a
asynchronous flush (triggered by flush_time), would cause the
server to crash.

The problem was that a hook used to detach client API handles
wasn't prepared to handle cases where the thread does not have
a associated session.

The solution is to verify whether the thread has a associated
session before trying to detach a handle.

mysql-test/r/federated_debug.result:
  Add test case result for Bug#47525
mysql-test/t/federated_debug-master.opt:
  Debug point.
mysql-test/t/federated_debug.test:
  Add test case for Bug#47525
sql/slave.cc:
  Check whether a the thread has a associated session.
sql/sql_parse.cc:
  Add debug code to simulate a reload without thread session.

mysql-test/r/federated_debug.result

+stop slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+start slave;
+stop slave;
+DROP DATABASE IF EXISTS federated;
+CREATE DATABASE federated;
+DROP DATABASE IF EXISTS federated;
+CREATE DATABASE federated;
+#
+# Bug#47525: MySQL crashed (Federated)
+#
+# Switch to slave
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (1);
+# Switch to master
+CREATE TABLE t1(a INT) ENGINE=FEDERATED
+CONNECTION='mysql://root@127.0.0.1:SLAVE_PORT/test/t1';
+SELECT * FROM t1;
+a
+1
+# Start a asynchronous reload
+# Wait for tables to be closed
+# Ensure that the server didn't crash
+SELECT * FROM t1;
+a
+1
+# Drop tables on master and slave
+DROP TABLE t1;
+DROP TABLE t1;
+# Federated cleanup
+DROP TABLE IF EXISTS federated.t1;
+DROP DATABASE IF EXISTS federated;
+DROP TABLE IF EXISTS federated.t1;
+DROP DATABASE IF EXISTS federated;

mysql-test/t/federated_debug-master.opt

+--loose-debug=d,simulate_detached_thread_refresh

mysql-test/t/federated_debug.test

+--source include/have_debug.inc
+--source include/federated.inc
+
+--echo #
+--echo # Bug#47525: MySQL crashed (Federated)
+--echo #
+
+connection slave;
+--echo # Switch to slave
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (1);
+
+connection master;
+--echo # Switch to master
+--replace_result $SLAVE_MYPORT SLAVE_PORT
+eval CREATE TABLE t1(a INT) ENGINE=FEDERATED
+  CONNECTION='mysql://root@127.0.0.1:$SLAVE_MYPORT/test/t1';
+
+SELECT * FROM t1;
+
+--echo # Start a asynchronous reload
+--exec $MYSQLADMIN --no-defaults -S $MASTER_MYSOCK -P $MASTER_MYPORT  -u root --password= refresh 2>&1
+
+--echo # Wait for tables to be closed
+let $show_statement= SHOW STATUS LIKE 'Open_tables';
+let $field= Value;
+let $condition= = '0';
+--source include/wait_show_condition.inc
+
+--echo # Ensure that the server didn't crash
+SELECT * FROM t1;
+--echo # Drop tables on master and slave
+DROP TABLE t1;
+connection slave;
+DROP TABLE t1;
+
+connection default;
+--echo # Federated cleanup
+source include/federated_cleanup.inc;

sql/slave.cc

@@ -4756,7 +4756,7 @@ extern "C" void slave_io_thread_detach_vio()
 {
 #ifdef SIGNAL_WITH_VIO_CLOSE
   THD *thd= current_thd;
-  if (thd->slave_thread)
+  if (thd && thd->slave_thread)
     thd->clear_active_vio();
 #endif
 }

sql/sql_parse.cc

@@ -2161,6 +2161,26 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
     if (check_global_access(thd,RELOAD_ACL))
       break;
     mysql_log.write(thd,command,NullS);
+#ifndef DBUG_OFF
+    DBUG_EXECUTE_IF("simulate_detached_thread_refresh",
+                    {
+                      /*
+                        Simulate a reload without a attached thread session.
+                        Provides a environment similar to that of when the
+                        server receives a SIGHUP signal and reloads caches
+                        and flushes tables.
+                      */
+                      bool res;
+                      my_pthread_setspecific_ptr(THR_THD, NULL);
+                      res= reload_acl_and_cache(NULL, options | REFRESH_FAST,
+                                                NULL, &not_used);
+                      my_pthread_setspecific_ptr(THR_THD, thd);
+                      if (!res)
+                        send_ok(thd);
+                      break;
+                    }
+                    );
+#endif
     if (!reload_acl_and_cache(thd, options, (TABLE_LIST*) 0, &not_used))
       send_ok(thd);
     break;