Limiting the number of threads used by PubSub publisher

PubSubThreads.java

//Thanks to ajaaym https://github.com/googleapis/java-pubsub/issues/27#issuecomment-538508100
final ExecutorProvider fixedExecutorProvider = FixedExecutorProvider.create(
        new ScheduledThreadPoolExecutor(1)); //adjust the size
    Publisher publisher =
        Publisher.newBuilder("topic_name")
            .setExecutorProvider(fixedExecutorProvider)
            .setChannelProvider(
                PublisherStubSettings.defaultGrpcTransportProviderBuilder()
                    .setExecutorProvider(fixedExecutorProvider)
                    .setChannelConfigurator(
                        new ApiFunction<ManagedChannelBuilder, ManagedChannelBuilder>() {
                          @Override
                          public ManagedChannelBuilder apply(
                              ManagedChannelBuilder managedChannelBuilder) {
                            NettyChannelBuilder nettyChannelBuilder =
                                (NettyChannelBuilder)
                                    managedChannelBuilder.executor(
                                        fixedExecutorProvider.getExecutor());
                            nettyChannelBuilder.eventLoopGroup(
                                new NioEventLoopGroup(1, fixedExecutorProvider.getExecutor()));
                              nettyChannelBuilder.channelType(
                                  NioSocketChannel.class); // Use EPoll if available, if using EPoll update above line to use EPollEventLoopGroup

                            return nettyChannelBuilder;
                          }
                        })
                    .build())
            .build();
    publisher.publish(PubsubMessage.newBuilder().setData(ByteString.copyFromUtf8("testdata")).build()).get();