MINOR: Move lock method outside try block

[g1geordie]

The Lock.lock in the try block may cause Lock.unlock throw exception when it throw exception .
I think it's nice to move outside although ReentrantLock.lock impl doesn't throw exception.

 class X {
   private final ReentrantLock lock = new ReentrantLock();
   // ...

   public void m() {
     lock.lock();  // block until condition holds
     try {
       // ... method body
     } finally {
       lock.unlock()
     }
   }
 }

pattern recommended by
https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/locks/ReentrantLock.html

[g1geordie]

@chia7712 can you help me to take a look?

[chia7712]

@g1geordie LGTM. thanks for you patch. I will merge it tomorrow if no objection.