mdev-201 - Assertion `!thd->spcont' failed in net_send_error on server shutdown

bug in semisync plugin. It didn't check thd->killed before waiting on mysys->current_cond,
and thus an attepmt to kill the thread (on shutdown) was lost

plugin/semisync/semisync_master.cc:
  mdev:201 lp:962540

plugin/semisync/semisync_master.cc

@@ -626,7 +626,7 @@ int ReplSemiSyncMaster::commitTrx(const char* trx_wait_binlog_name,
                             (int)is_on());
     }
 
-    while (is_on())
+    while (is_on() && !thd_killed(NULL))
     {
       if (reply_file_name_inited_)
       {
@@ -743,7 +743,8 @@ int ReplSemiSyncMaster::commitTrx(const char* trx_wait_binlog_name,
       At this point, the binlog file and position of this transaction
       must have been removed from ActiveTranx.
     */
-    assert(!active_tranxs_->is_tranx_end_pos(trx_wait_binlog_name,
+    assert(thd_killed(NULL) ||
+           !active_tranxs_->is_tranx_end_pos(trx_wait_binlog_name,
                                              trx_wait_binlog_pos));
     
     /* Update the status counter. */

sql/sql_class.cc

@@ -3735,6 +3735,9 @@ void THD::restore_backup_open_tables_state(Open_tables_backup *backup)
 
 extern "C" int thd_killed(const MYSQL_THD thd)
 {
+  if (!thd)
+    thd= current_thd;
+
   if (!(thd->killed & KILL_HARD_BIT))
     return 0;
   return thd->killed;