Check for global read lock on MySQL

Can I check whether a global read lock is in place?

My application uses MySQL (actually MariaDB) on InnoDB. I’m going to run mysqldump --all-databases, which will impose a global read lock for an hour. I’d like my application to check for the existence of this lock, but it doesn’t appear to show up in anything I’ve tried (unless a request which is waiting on the lock already exists):

• SHOW ENGINE INNODB STATUS
• SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCKS
• SHOW FULL PROCESSLIST