default void preSwitchRpcThrottle(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final boolean enable) throws IOException {
  }
Called before switching rpc throttle enabled state.
@param ctx    the coprocessor instance's environment
@param enable the rpc throttle value
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java