protected final ExecutorService getExecutor() {
        lock.readLock().lock();
        try {
            ensureInitialized();
            return executor;
        } finally {
            lock.readLock().unlock();
        }
    }
Gets executor service for this client.

@return executor service
@throws IllegalStateException when the client is either closed or not
                              initialized
clickhouse-client/src/main/java/com/clickhouse/client/AbstractClient.java