InnoDB: tolerate system clock glitches a little better

in the error monitor thread.  (Bug #5898)


innobase/include/sync0arr.h:
  sync_array_print_long_waits(): return error status
innobase/srv/srv0srv.c:
  srv_error_monitor_thread(): Keep track on successive fatal timeouts,
  and crash the server only if the timeouts have been exceeded for
  several times in succession.
innobase/sync/sync0arr.c:
  sync_array_print_long_waits(): return error status

innobase/include/sync0arr.h

@@ -97,9 +97,11 @@ sync_arr_wake_threads_if_sema_free(void);
 /**************************************************************************
 Prints warnings of long semaphore waits to stderr. */
 
-void
+ibool
 sync_array_print_long_waits(void);
 /*=============================*/
+			/* out: TRUE if fatal semaphore wait threshold
+			was exceeded */
 /************************************************************************
 Validates the integrity of the wait array. Checks
 that the number of reserved cells equals the count variable. */

innobase/srv/srv0srv.c

@@ -1754,7 +1754,8 @@ srv_error_monitor_thread(
 			/* in: a dummy parameter required by
 			os_thread_create */
 {
-	ulint	cnt	= 0;
+	/* number of successive fatal timeouts observed */
+	ulint	fatal_cnt	= 0;
 
 #ifdef UNIV_DEBUG_THREAD_CREATION
 	fprintf(stderr, "Error monitor thread starts, id %lu\n",
@@ -1763,8 +1764,6 @@ srv_error_monitor_thread(
 loop:
 	srv_error_monitor_active = TRUE;
 
-	cnt++;
-
 	os_thread_sleep(2000000);
 
 	if (difftime(time(NULL), srv_last_monitor_time) > 60) {
@@ -1774,7 +1773,20 @@ loop:
 		srv_refresh_innodb_monitor_stats();
 	}
 
-	sync_array_print_long_waits();
+	if (sync_array_print_long_waits()) {
+		fatal_cnt++;
+		if (fatal_cnt > 5) {
+
+			fprintf(stderr,
+"InnoDB: Error: semaphore wait has lasted > %lu seconds\n"
+"InnoDB: We intentionally crash the server, because it appears to be hung.\n",
+				srv_fatal_semaphore_wait_threshold);
+
+			ut_error;
+		}
+	} else {
+		fatal_cnt = 0;
+	}
 
 	/* Flush stderr so that a database user gets the output
 	to possible MySQL error file */

innobase/sync/sync0arr.c

@@ -889,15 +889,18 @@ sync_arr_wake_threads_if_sema_free(void)
 /**************************************************************************
 Prints warnings of long semaphore waits to stderr. */
 
-void
+ibool
 sync_array_print_long_waits(void)
 /*=============================*/
+			/* out: TRUE if fatal semaphore wait threshold
+			was exceeded */
 {
         sync_cell_t*   	cell;
         ibool		old_val;
 	ibool		noticed = FALSE;
 	ulint           i;
 	ulint		fatal_timeout = srv_fatal_semaphore_wait_threshold;
+	ibool		fatal = FALSE;
 
         for (i = 0; i < sync_primary_wait_array->n_cells; i++) {
 
@@ -914,13 +917,7 @@ sync_array_print_long_waits(void)
                 if (cell->wait_object != NULL
 		    && difftime(time(NULL), cell->reservation_time)
 		    > fatal_timeout) {
-
-			fprintf(stderr,
-"InnoDB: Error: semaphore wait has lasted > %lu seconds\n"
-"InnoDB: We intentionally crash the server, because it appears to be hung.\n",
-				fatal_timeout);
-
-		    	ut_error;
+			fatal = TRUE;
                 }
        	}
 
@@ -948,6 +945,8 @@ sync_array_print_long_waits(void)
 		fprintf(stderr,
 "InnoDB: ###### Diagnostic info printed to the standard error stream\n");
 	}
+
+	return(fatal);
 }
 
 /**************************************************************************