@Override
        public AtomicInteger load(Address key) throws Exception {
          return new AtomicInteger(0);
        }
Provides the basics for a RpcClient implementation like configuration and Logging.
<p>
Locking schema of the current IPC implementation
<ul>
<li>There is a lock in {@link AbstractRpcClient} to protect the fetching or creating
connection.</li>
<li>There is a lock in {@link Call} to make sure that we can only finish the call once.</li>
<li>The same for {@link HBaseRpcController} as {@link Call}. And see the comment of
{@link HBaseRpcController#notifyOnCancel(RpcCallback, HBaseRpcController.CancellationCallback)}
of how to deal with cancel.</li>
<li>For connection implementation, the construction of a connection should be as fast as possible
because the creation is protected under a lock. Connect to remote side when needed. There is no
forced locking schema for a connection implementation.</li>
<li>For the locking order, the {@link Call} and {@link HBaseRpcController}'s lock should be held
at last. So the callbacks in {@link Call} and {@link HBaseRpcController} should be execute
outside the lock in {@link Call} and {@link HBaseRpcController} which means the implementations
of the callbacks are free to hold any lock.</li>
</ul>
@since 2.0.0
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java