title: What is the meaning of "ReentrantLock" in Java?
body: <p>Reentrancy means that locks are acquired on a per-thread rather than per-invocation basis.</p>
  
  <p>Since an intrinsic lock is held by a thread, doesn't it mean that a thread run once equals an invocation basis?</p>
  
  <p>Thank you, it seems mean that: in a thread,if I get a lock <code>lockA</code> when process function <code>doA</code> which call function <code>doB</code>, and <code>doB</code> also need a lock <code>lockA</code>,then there wil be a reentrancy. In Java, this phenomenon is acquired per thread, so I needn't consider deadlocks?</p>