MDEV-20612: Replace lock_sys.mutex with lock_sys.latch

For now, we will acquire the lock_sys.latch only in exclusive mode,
that is, use it as a mutex.

This is preparation for the next commit where we will introduce
a less intrusive alternative, combining a shared lock_sys.latch
with dict_table_t::lock_mutex or a mutex embedded in
lock_sys.rec_hash, lock_sys.prdt_hash, or lock_sys.prdt_page_hash.

1 files changed, 8 insertions, 15 deletions

diff --git a/storage/innobase/srv/srv0srv.cc b/storage/innobase/srv/srv0srv.cc
index 39d358a7165..d75451ce791 100644
--- a/storage/innobase/srv/srv0srv.cc
+++ b/storage/innobase/srv/srv0srv.cc
@@ -456,19 +456,13 @@ lock			--	semaphore;
 kernel			--	kernel;
 
 query thread execution:
-(a) without lock mutex
+(a) without lock_sys.latch
 reserved		--	process executing in user mode;
-(b) with lock mutex reserved
+(b) with lock_sys.latch reserved
 			--	process executing in kernel mode;
 
-The server has several backgroind threads all running at the same
-priority as user threads. It periodically checks if here is anything
-happening in the server which requires intervention of the master
-thread. Such situations may be, for example, when flushing of dirty
-blocks is needed in the buffer pool or old version of database rows
-have to be cleaned away (purged). The user can configure a separate
-dedicated purge thread(s) too, in which case the master thread does not
-do any purging.
+The server has several background threads all running at the same
+priority as user threads.
 
 The threads which we call user threads serve the queries of the MySQL
 server. They run at normal priority.
@@ -800,7 +794,7 @@ srv_printf_innodb_monitor(
 	/* Only if lock_print_info_summary proceeds correctly,
 	before we call the lock_print_info_all_transactions
 	to print all the lock information. IMPORTANT NOTE: This
-	function acquires the lock mutex on success. */
+	function acquires exclusive lock_sys.latch on success. */
 	ret = lock_print_info_summary(file, nowait);
 
 	if (ret) {
@@ -813,9 +807,8 @@ srv_printf_innodb_monitor(
 			}
 		}
 
-		/* NOTE: If we get here then we have the lock mutex. This
-		function will release the lock mutex that we acquired when
-		we called the lock_print_info_summary() function earlier. */
+		/* NOTE: The following function will release the lock_sys.latch
+		that lock_print_info_summary() acquired. */
 
 		lock_print_info_all_transactions(file);
 
@@ -1235,7 +1228,7 @@ static void srv_monitor()
 		if (srv_print_innodb_monitor) {
 			/* Reset mutex_skipped counter everytime
 			srv_print_innodb_monitor changes. This is to
-			ensure we will not be blocked by lock_sys.mutex
+			ensure we will not be blocked by lock_sys.latch
 			for short duration information printing */
 			if (!monitor_state.last_srv_print_monitor) {
 				monitor_state.mutex_skipped = 0;