message: Fix gracefull shutdown hanging
diff: @@ -51,6 +51,7 @@ pub struct MempoolPrevalidator {
  enum Event {
  NewHead(BlockHash, Level),
  ValidateOperation(OperationHash, MempoolOperationType),
  + ShuttingDown,
  }
  /// Reference to [chain feeder](ChainFeeder) actor
  @@ -138,6 +139,11 @@ impl MempoolPrevalidator {
  Event::ValidateOperation(operation.operation_hash.clone(), operation.operation_type)
  )?;
  }
  + ShellChannelMsg::ShuttingDown(_) => {
  + self.validator_event_sender.lock().unwrap().send(
  + Event::ShuttingDown
  + )?;
  + }
  _ => ()
  }
  @@ -363,6 +369,9 @@ fn process_prevalidation(
  debug!(log, "Mempool - received validate operation event - operations was previously validated and removed from mempool storage"; "hash" => HashType::OperationHash.bytes_to_string(&oph));
  }
  }
  + Event::ShuttingDown => {
  + validator_run.store(false, Ordering::Release);
  + }
  }
  }
  