Condition - should unlock before await?

Question

Could you tell me if I should release lock before await on condition?

try {
    lock.lock();
    while (isNotEmpty()) {
        condition.await();
    }
} finally {
    lock.unlock();
}

Or

try {
    lock.lock();
    while (isNotEmpty()) {
        lock.unlock();
        condition.await();
    }
} finally {
    lock.unlock();
}

Answer 1

No, you do not need to explicitly release the lock before calling await, await will release it automatically. From javadoc:

The lock associated with this Condition is atomically released and the current thread becomes disabled for thread scheduling purposes[...]

And:

The current thread is assumed to hold the lock associated with this Condition when this method is called.

Answer 2

You can only await() on a Condition when you have lock()ed the associated Lock

Why don't you have a condition for isEmpty to make your conditions clearer.

See the example in the Javadoc. http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/Condition.html

e.g.

 lock.lock();
 try {
   while (count > 0)
     isEmpty.await();
   // do something when empty.
 } finally {
   lock.unlock();
 }