Java ReentrantReadWriteLock 同一个线程先 readlock, 再 witelock 死锁 - dead lock

• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/ReentrantReadWriteLock.html
  

Lock downgrading

Reentrancy also allows downgrading from the write lock to a read lock, by acquiring the write lock, then the read lock and then releasing the write lock. However, upgrading from a read lock to the write lock is not possible.

• Refer to https://josephmate.github.io/2020-02-24-deadlock-who-owns-the-lock/

What I Learned

1. Locking a readlock, then locking the write lock on the same lock creates a deadlock.
2. Deadlocks created using locks instead of monitors does not appear in thread dumps (like those created by kill -3 (linux) or Ctrl+Break (windows)).
3. Keep digging and you’ll uncover a nasty incorrect assumption you’ve been making.
4. -XX:+PrintConcurrentLocks detects some deadlocks
5. -XX:+PrintConcurrentLocks does not print reentrant locks on stack traces
6. -XX:+PrintConcurrentLocks does not detect acquiring read then write lock in the same thread deadlock