Speed up connection time:

-Change my_rnd() slightly to make it safer if two threads use it at the same time.
-Avoid some sprintf and strmov in vio.
-Changed thread_count to be automically incremented (instead of under LOCK_thread_count).
-Thread cache now uses LOCK_thread_cache instead of LOCK_thread_count.
-Moved delete thd out from LOCK_thread_count.
-Save some mysql_cond_broadcast(&COND_thread_count) calls.
-Removed call to getsockname() during connect.
-Initialize random generator without locks.

Other things:
-Added thread_safe_decrement32() and thread_safe_increment32()
-Removed sql_rnd_with_mutex() and get_thread_running()

Thanks to Yoshinori Matsunobu for the benchmark of connection speed and to
Domas Mituzas for the inspiration for many of the fixes.
 

include/violite.h:
  Change desc to a string pointer
mysql-test/suite/perfschema/r/all_instances.result:
  Added new mutex
mysys/my_rnd.c:
  Change my_rnd() slightly to make it safer if two threads use it at the same time.
sql/event_scheduler.cc:
  Changed thread_count to be automically incremented
  Moved some safe things out from LOCK_thread_count.
  Simplify deleting of THD for running thread.
sql/mysqld.cc:
  Changed thread_count to be automically incremented
  Thread cache now uses LOCK_thread_cache instead of LOCK_thread_count
  Added delete_running_thd()
  Moved delete thd out from LOCK_thread_count
  More DBUG_ENTER
  Only call  mysql_cond_broadcast(&COND_thread_count) if thread_count is 0
  Removed call to getsockname() (old not anymore needed check)
sql/mysqld.h:
  Removed sql_rnd_with_mutex() (not needed anymore)
  Removed not used function get_thread_running()
  Added thread_safe_decrement32() and thread_safe_increment32()
  Simplified dec_thread_running() and inc_thread_running()
sql/sql_class.cc:
  Removed thd_lock_thread_count() and thd_unlock_thread_count()
  Initialize random generator without locks
sql/sql_insert.cc:
  Changed thread_count to be automically incremented
sql/sql_parse.cc:
  Changed thread_count to be automically incremented
vio/vio.c:
  Don't generate 'desc' with sprintf/strmov. Assign a pointer instead.
  (Good enough as this is just for debugging)

include/violite.h

@@ -216,7 +216,7 @@ struct st_vio
   struct sockaddr_storage	remote;		/* Remote internet address */
   int addrLen;                          /* Length of remote address */
   enum enum_vio_type	type;		/* Type of connection */
-  char			desc[30];	/* String description */
+  const char		*desc;		/* String description */
   char                  *read_buffer;   /* buffer for vio_read_buff */
   char                  *read_pos;      /* start of unfetched data in the
                                            read buffer */