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, 4 insertions, 6 deletions

diff --git a/sql/rpl_parallel.cc b/sql/rpl_parallel.cc
index b4e7b1a89dd..286162efcb8 100644
--- a/sql/rpl_parallel.cc
+++ b/sql/rpl_parallel.cc
@@ -969,10 +969,8 @@ handle_rpl_parallel_thread(void *arg)
   my_thread_init();
   thd = new THD;
   thd->thread_stack = (char*)&thd;
-  mysql_mutex_lock(&LOCK_thread_count);
-  thd->thread_id= thd->variables.pseudo_thread_id= thread_id++;
-  threads.append(thd);
-  mysql_mutex_unlock(&LOCK_thread_count);
+  thd->thread_id= thd->variables.pseudo_thread_id= next_thread_id();
+  add_to_active_threads(thd);
   set_current_thd(thd);
   pthread_detach_this_thread();
   thd->init_for_queries();
@@ -1372,10 +1370,10 @@ handle_rpl_parallel_thread(void *arg)
   thd->reset_db(NULL, 0);
   thd_proc_info(thd, "Slave worker thread exiting");
   thd->temporary_tables= 0;
-  mysql_mutex_lock(&LOCK_thread_count);
+
   THD_CHECK_SENTRY(thd);
+  unlink_not_visible_thd(thd);
   delete thd;
-  mysql_mutex_unlock(&LOCK_thread_count);
 
   mysql_mutex_lock(&rpt->LOCK_rpl_thread);
   rpt->running= false;