code: public DefaultShardManagerBuilder setGatewayPool(ScheduledExecutorService pool, boolean automaticShutdown)
      {
          return setGatewayPoolProvider(pool == null ? null : new ThreadPoolProviderImpl<>(pool, automaticShutdown));
      }
docs: Sets the {@link ScheduledExecutorService ScheduledExecutorService} that should be used for
  the JDA main WebSocket workers.
  <br><b>Only change this pool if you know what you're doing.</b>
  <br>This will override the worker pool provider set from {@link #setGatewayPoolProvider(ThreadPoolProvider)}.
  
  @param  pool
  The thread-pool to use for main WebSocket workers
  @param  automaticShutdown
  Whether {@link net.dv8tion.jda.core.JDA#shutdown()} should automatically shutdown this pool
  
  @return The DefaultShardManagerBuilder instance. Useful for chaining.