MDEV-7189: main.processlist fails sporadically in buildbot

The test case tried to trigger a DEBUG_SYNC point at the end of a SELECT
SLEEP(5) statement. It did this by using EXECUTE 2, intending to trigger first
at the end of SET DEBUG_SYNC, and second at the end of the SELECT SLEEP(5).

However, in --ps-protocol mode, this does not work, because the SELECT is
executed in two steps (Prepare followed by Execute). Thus, the DEBUG_SYNC got
triggered too early, during the Prepare stage rather than Execute, and the
test case could race and information_schema.processlist see the thread in the
wrong state.

This patch fixes by changing the way the DEBUG_SYNC point is triggered. Now we
add a DBUG injection inside the code for SLEEP(5). This ensures that the
DEBUG_SYNC point is not activated until the SLEEP(5) is running, ensuring
that the following wait for completion will be effective.

mysql-test/mysql-test-run.pl

@@ -2495,6 +2495,7 @@ sub environment_setup {
   # ----------------------------------------------------
   my $exe_replace= mtr_exe_exists(vs_config_dirs('extra', 'replace'),
                                  "$basedir/extra/replace",
+                                 "$bindir/extra$opt_vs_config/replace",
                                  "$path_client_bindir/replace");
   $ENV{'REPLACE'}= native_path($exe_replace);
 

mysql-test/r/processlist.result

@@ -7,9 +7,8 @@ SELECT ID, TIME,TIME_MS FROM INFORMATION_SCHEMA.PROCESSLIST WHERE CONCAT(":", ID
 SET DEBUG_SYNC = 'now SIGNAL fill_schema_proceed';
 ID	TIME	TIME_MS
 TID	0	0.000
-SET DEBUG_SYNC = 'dispatch_command_end SIGNAL query_done EXECUTE 2';
-SET DEBUG_SYNC= 'now WAIT_FOR query_done';
-SET DEBUG_SYNC= 'now SIGNAL nosignal';
+set debug_sync='reset';
+SET debug_dbug="+d,sleep_inject_query_done_debug_sync";
 select sleep(5);
 sleep(5)
 0

mysql-test/t/processlist.test

@@ -2,6 +2,7 @@
 # MDEV-4578 information_schema.processlist reports incorrect value for Time (2147483647)
 #
 
+source include/have_debug.inc;
 source include/have_debug_sync.inc;
 
 let $tid= `SELECT CONNECTION_ID()`;
@@ -21,6 +22,7 @@ SET DEBUG_SYNC = 'now SIGNAL fill_schema_proceed';
 connection con1;
 --replace_result $tid TID
 reap;
+set debug_sync='reset';
 connection default;
 
 #
@@ -28,15 +30,13 @@ connection default;
 #
 
 connection con1;
-# Trigger a signal once the thread has gone from "Query" to "Sleep" command
-# state. Note we need to execute this twice: Once at the end of SET DEBUG_SYNC,
-# and once for the intended time, at the end of SELECT SLEEP().
-SET DEBUG_SYNC = 'dispatch_command_end SIGNAL query_done EXECUTE 2';
-connection default;
-# Wait for and clear the first signal set during SET DEBUG_SYNC.
-SET DEBUG_SYNC= 'now WAIT_FOR query_done';
-SET DEBUG_SYNC= 'now SIGNAL nosignal';
-connection con1;
+# This DBUG insertion triggers a DEBUG_SYNC signal "query_done" once
+# the below SELECT SLEEP(5) has gone from "Query" to "Sleep" command
+# state. (We cannot just set the DEBUG_SYNC directly here, because
+# then it can trigger at the end of the SET DEBUG_SYNC statement (or
+# at the end of the Prepare step of the SELECT, if --ps-protocol),
+# thus occuring too early).
+SET debug_dbug="+d,sleep_inject_query_done_debug_sync";
 select sleep(5); #run a query that will take some time
 connection default;
 

sql/item_func.cc

@@ -4482,6 +4482,11 @@ longlong Item_func_sleep::val_int()
 
   mysql_cond_destroy(&cond);
 
+  DBUG_EXECUTE_IF("sleep_inject_query_done_debug_sync", {
+      debug_sync_set_action
+        (thd, STRING_WITH_LEN("dispatch_command_end SIGNAL query_done"));
+    };);
+
   return test(!error); 		// Return 1 killed
 }