MDEV-6150 Speed up connection speed by moving creation of THD to new thread

Creating a CONNECT object on client connect and pass this to the working thread which creates the THD.
Split LOCK_thread_count to different mutexes
Added LOCK_thread_start to syncronize threads
Moved most usage of LOCK_thread_count to dedicated functions
Use next_thread_id() instead of thread_id++

Other things:
- Thread id now starts from 1 instead of 2
- Added cast for thread_id as thread id is now of type my_thread_id
- Made THD->host const (To ensure it's not changed)
- Removed some DBUG_PRINT() about entering/exiting mutex as these was already logged by mutex code
- Fixed that aborted_connects and connection_errors_internal are counted in all cases
- Don't take locks for current_linfo when we set it (not needed as it was 0 before)

1 files changed, 35 insertions, 1 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index a15a738b1bf..2c8270055db 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -1185,7 +1185,8 @@ public:
     priv_user - The user privilege we are using. May be "" for anonymous user.
     ip - client IP
   */
-  char   *host, *user, *ip;
+  const char *host;
+  char   *user, *ip;
   char   priv_user[USERNAME_LENGTH];
   char   proxy_user[USERNAME_LENGTH + MAX_HOSTNAME + 5];
   /* The host privilege we are using */
@@ -4027,8 +4028,41 @@ public:
   {
     main_lex.restore_set_statement_var();
   }
+
+  /*
+    Reset current_linfo
+    Setting current_linfo to 0 needs to be done with LOCK_thread_count to
+    ensure that adjust_linfo_offsets doesn't use a structure that may
+    be deleted.
+  */
+  inline void reset_current_linfo()
+  {
+    mysql_mutex_lock(&LOCK_thread_count);
+    current_linfo= 0;
+    mysql_mutex_unlock(&LOCK_thread_count);
+  }
 };
 
+inline void add_to_active_threads(THD *thd)
+{
+  mysql_mutex_lock(&LOCK_thread_count);
+  threads.append(thd);
+  mysql_mutex_unlock(&LOCK_thread_count);
+}
+
+/*
+  This should be called when you want to delete a thd that was not
+  running any queries.
+  This function will assert if the THD was not linked.
+*/
+
+inline void unlink_not_visible_thd(THD *thd)
+{
+  thd->assert_if_linked();
+  mysql_mutex_lock(&LOCK_thread_count);
+  thd->unlink();
+  mysql_mutex_unlock(&LOCK_thread_count);
+}
 
 /** A short cut for thd->get_stmt_da()->set_ok_status(). */