MDEV-3917 multiple use locks (GET_LOCK) in one connection.

    The patch contributed by Konstantin Osipov applied.
    Native comments:
      Implement multiple user-level locks per connection.

      GET_LOCK() function in MySQL allows a connection  to hold at most
      one user level lock. Taking a new lock automatically releases the
      old lock, if any.

      The limit of one lock per session existed since  early versions
      of MySQL didn't have a deadlock detector for SQL locks.
      MDL patches in MySQL 5.5 added a deadlock detector,
      so starting from 5.5 it became possible to take multiple locks
      in any order -- a deadlock, should it occur, would be detected
      and an error returned to the client which closed the wait chain.

      This is exactly what is done in this patch: ULLs are moved
      to use MDL subsystem.

1 files changed, 15 insertions, 10 deletions

diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 95aa4a00122..caf56f9f84c 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -827,6 +827,7 @@ THD::THD()
   col_access=0;
   is_slave_error= thread_specific_used= FALSE;
   my_hash_clear(&handler_tables_hash);
+  my_hash_clear(&ull_hash);
   tmp_table=0;
   cuted_fields= 0L;
   sent_row_count= 0L;
@@ -866,7 +867,6 @@ THD::THD()
   net.vio=0;
   net.buff= 0;
   client_capabilities= 0;                       // minimalistic client
-  ull=0;
   system_thread= NON_SYSTEM_THREAD;
   cleanup_done= abort_on_warning= 0;
   peer_port= 0;					// For SHOW PROCESSLIST
@@ -1400,8 +1400,6 @@ void THD::cleanup(void)
   if (global_read_lock.is_acquired())
     global_read_lock.unlock_global_read_lock(this);
 
-  /* All metadata locks must have been released by now. */
-  DBUG_ASSERT(!mdl_context.has_locks());
   if (user_connect)
   {
     decrease_user_connections(user_connect);
@@ -1419,13 +1417,9 @@ void THD::cleanup(void)
   sp_cache_clear(&sp_proc_cache);
   sp_cache_clear(&sp_func_cache);
 
-  if (ull)
-  {
-    mysql_mutex_lock(&LOCK_user_locks);
-    item_user_lock_release(ull);
-    mysql_mutex_unlock(&LOCK_user_locks);
-    ull= NULL;
-  }
+  mysql_ull_cleanup(this);
+  /* All metadata locks must have been released by now. */
+  DBUG_ASSERT(!mdl_context.has_locks());
 
   apc_target.destroy();
   cleanup_done=1;
@@ -4001,6 +3995,15 @@ extern "C" unsigned long thd_get_thread_id(const MYSQL_THD thd)
 }
 
 
+/**
+  Check if THD socket is still connected.
+ */
+extern "C" int thd_is_connected(MYSQL_THD thd)
+{
+  return thd->is_connected();
+}
+
+
 #ifdef INNODB_COMPATIBILITY_HOOKS
 extern "C" const struct charset_info_st *thd_charset(MYSQL_THD thd)
 {
@@ -4321,6 +4324,8 @@ void THD::leave_locked_tables_mode()
     /* Also ensure that we don't release metadata locks for open HANDLERs. */
     if (handler_tables_hash.records)
       mysql_ha_set_explicit_lock_duration(this);
+    if (ull_hash.records)
+      mysql_ull_set_explicit_lock_duration(this);
   }
   locked_tables_mode= LTM_NONE;
 }