DROP TABLE IF EXISTS t1;
SET DEBUG_SYNC= 'RESET';
CREATE TABLE t1 (kill_id INT);
INSERT INTO t1 VALUES(connection_id());
# Switching to connection 'default'.
# Start transaction.
BEGIN;
INSERT INTO t1 VALUES(connection_id());
# Ensure that COMMIT will pause once it acquires protection
# against its global read lock.
SET DEBUG_SYNC='ha_commit_trans_after_acquire_commit_lock SIGNAL acquired WAIT_FOR go';
# Sending:
COMMIT;
# Switching to 'con1'.
# Wait till COMMIT acquires protection against global read
# lock and pauses.
SET DEBUG_SYNC='now WAIT_FOR acquired';
# Sending:
FLUSH TABLES WITH READ LOCK;
# Switching to 'con2'.
SELECT ((@id := kill_id) - kill_id) FROM t1 LIMIT 1;
((@id := kill_id) - kill_id)
0
Warnings:
Warning	1287	Setting user variables within expressions is deprecated and will be removed in a future release. Consider alternatives: 'SET variable=expression, ...', or 'SELECT expression(s) INTO variables(s)'.
# Wait till FLUSH TABLES WITH READ LOCK blocks due
# to active COMMIT
# Kill connection 'con1'.
KILL CONNECTION @id;
# Switching to 'con1'.
# Try to reap FLUSH TABLES WITH READ LOCK, 
# it fail due to killed statement and connection.
Got one of the listed errors
# Switching to 'con2'.
# Resume COMMIT.
SET DEBUG_SYNC='now SIGNAL go';
# Switching to 'default'.
# Reaping COMMIT.
DROP TABLE t1;
SET DEBUG_SYNC= 'RESET';