public void cleanUp() {
    if (removalThread != null) {
      removalThread.shutdown();
    }
  }
Initializes the <code>Region</code> backing this queue. The <code>Region</code>'s scope is
DISTRIBUTED_NO_ACK and mirror type is KEYS_VALUES and is set to overflow to disk based on the
<code>GatewayQueueAttributes</code>.

@param sender The GatewaySender <code>SerialGatewaySenderImpl</code>
@param listener The GemFire <code>CacheListener</code>. The <code>CacheListener</code> can be
       null.
geode-core/src/main/java/org/apache/geode/internal/cache/wan/serial/SerialGatewaySenderQueue.java