Move all kill mutex protection to LOCK_thd_kill

LOCK_thd_data was used to protect both THD data and
ensure that the THD is not deleted while it was in use

This patch moves the THD delete protection to LOCK_thd_kill,
which already protects the THD for kill.

The benefits are:
- More well defined what LOCK_thd_data protects
- LOCK_thd_data usage is now much simpler and easier to verify
- Less chance of deadlocks in SHOW PROCESS LIST as there is less
  chance of interactions between mutexes
- Remove not needed LOCK_thread_count from
  thd_get_error_context_description()
- Fewer mutex taken for thd->awake()

Other things:
- Don't take mysys->var mutex in show processlist to check if thread
  is kill marked
- thd->awake() now automatically takes the LOCK_thd_kill mutex
  (Simplifies code)
- Apc uses LOCK_thd_kill instead of LOCK_thd_data

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/threadpool_common.cc b/sql/threadpool_common.cc
index 598951da406..98b2dcd1fcd 100644
--- a/sql/threadpool_common.cc
+++ b/sql/threadpool_common.cc
@@ -250,7 +250,7 @@ static THD* threadpool_add_connection(CONNECT *connect, void *scheduler_data)
   }
   delete connect;
   add_to_active_threads(thd);
-  thd->mysys_var= mysys_var;
+  thd->set_mysys_var(mysys_var);
   thd->event_scheduler.data= scheduler_data;
 
   /* Create new PSI thread for use with the THD. */
@@ -477,11 +477,11 @@ void tp_timeout_handler(TP_connection *c)
   if (c->state != TP_STATE_IDLE)
     return;
   THD *thd=c->thd;
-  mysql_mutex_lock(&thd->LOCK_thd_data);
+  mysql_mutex_lock(&thd->LOCK_thd_kill);
   thd->set_killed(KILL_WAIT_TIMEOUT);
   c->priority= TP_PRIORITY_HIGH;
   post_kill_notification(thd);
-  mysql_mutex_unlock(&thd->LOCK_thd_data);
+  mysql_mutex_unlock(&thd->LOCK_thd_kill);
 }