MDEV-18400 - Move shutdown handling to main thread

Signal handler is now respoinsible for setting abort_loop and breaking
poll() in main thread. The rest is handled by main thread itself.

Removed redundant LOCK_error_log init/destroy wrappers.
Removed redundant unireg_end(): it is trivial and it has only one caller.
Removed unused ready_to_exit from PFS.
Removed kill_in_progress: duplicates abort_loop.
Removed shutdown_in_progress: duplicates abort_loop.
Removed ready_to_exit: was used to make sure main thread waits for
cleanups, which are now done by main thread itself.
Removed SIGNALS_DONT_BREAK_READ, MAYBE_BROKEN_SYSCALL,
kill_broken_server: never defined/used.
Make clean_up() static.

plugin/feedback/sender_thread.cc

@@ -137,7 +137,7 @@ static int prepare_for_fill(TABLE_LIST *tables)
 */
 static bool going_down()
 {
-  return shutdown_plugin || shutdown_in_progress || (thd && thd->killed);
+  return shutdown_plugin || abort_loop || (thd && thd->killed);
 }
 
 /**

sql/init.h

@@ -17,6 +17,5 @@
 #define INIT_INCLUDED
 
 void unireg_init(ulong options);
-void unireg_end(void);
 
 #endif /* INIT_INCLUDED */

sql/mysqld.h

@@ -82,7 +82,7 @@ enum enum_slave_parallel_mode {
 };
 
 /* Function prototypes */
-void kill_mysql(THD *thd= 0);
+void kill_mysql(THD *thd);
 void close_connection(THD *thd, uint sql_errno= 0);
 void handle_connection_in_main_thread(CONNECT *thd);
 void create_thread_to_handle_connection(CONNECT *connect);
@@ -770,8 +770,6 @@ enum enum_query_type
 /* query_id */
 extern query_id_t global_query_id;
 
-void unireg_end(void);
-
 /* increment query_id and return it.  */
 inline __attribute__((warn_unused_result)) query_id_t next_query_id()
 {

sql/rpl_mi.cc

@@ -1436,7 +1436,7 @@ bool Master_info_index::add_master_info(Master_info *mi, bool write_to_file)
     We have to protect against shutdown to ensure we are not calling
     my_hash_insert() while my_hash_free() is in progress
   */
-  if (unlikely(shutdown_in_progress) ||
+  if (unlikely(abort_loop) ||
       !my_hash_insert(&master_info_hash, (uchar*) mi))
   {
     if (global_system_variables.log_warnings > 1)
@@ -1579,7 +1579,7 @@ uint any_slave_sql_running(bool already_locked)
 
   if (!already_locked)
     mysql_mutex_lock(&LOCK_active_mi);
-  if (unlikely(shutdown_in_progress || !master_info_index))
+  if (unlikely(abort_loop || !master_info_index))
     count= 1;
   else
   {

sql/sql_class.h

@@ -184,8 +184,6 @@ extern char internal_table_name[2];
 extern char empty_c_string[1];
 extern MYSQL_PLUGIN_IMPORT const char **errmesg;
 
-extern bool volatile shutdown_in_progress;
-
 extern "C" LEX_STRING * thd_query_string (MYSQL_THD thd);
 extern "C" size_t thd_query_safe(MYSQL_THD thd, char *buf, size_t buflen);
 

sql/wsrep_mysqld.cc

@@ -2403,10 +2403,10 @@ void wsrep_kill_mysql(THD *thd)
 {
   if (mysqld_server_started)
   {
-    if (!shutdown_in_progress)
+    if (!abort_loop)
     {
       WSREP_INFO("starting shutdown");
-      kill_mysql();
+      kill_mysql(thd);
     }
   }
   else

storage/perfschema/unittest/pfs_server_stubs.cc

@@ -24,8 +24,6 @@
 
 struct sql_digest_storage;
 
-volatile bool ready_to_exit= false;
-
 uint lower_case_table_names= 0;
 CHARSET_INFO *files_charset_info= NULL;
 CHARSET_INFO *system_charset_info= NULL;