How to send Messages in spring boot via websocket broker in the order they were submitted?

Question

I want to configure a spring boot websocket message broker such that it dispatches messages in the order they were submitted.

Based on answers to similar questions, I have tried to set the pool size of the dispatching task executors to 1, but I still get messages dispatched in the wrong order.

For debugging purposes I have added pre- and post-send channel interceptors which log the threads on which the messages are being dispatched and I can see that the Thread IDs vary.

What I am I doing wrong?

Code (Kotlin):

Websocket configuration:

package foo.bar

import org.slf4j.LoggerFactory
import org.springframework.context.annotation.Configuration
import org.springframework.messaging.Message
import org.springframework.messaging.MessageChannel
import org.springframework.messaging.simp.config.ChannelRegistration
import org.springframework.messaging.simp.config.MessageBrokerRegistry
import org.springframework.messaging.support.ChannelInterceptor
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker
import org.springframework.web.socket.config.annotation.StompEndpointRegistry
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer

@Configuration
@EnableWebSocketMessageBroker
class WebSocketConfig : WebSocketMessageBrokerConfigurer{
    companion object {
        private val LOGGER = LoggerFactory.getLogger(WebSocketConfig::class.java)
    }
    override fun configureMessageBroker(config: MessageBrokerRegistry) {
        config.enableSimpleBroker("/topic")
        config.setApplicationDestinationPrefixes("/app");
        config.configureBrokerChannel().taskExecutor().corePoolSize(1)
        config.configureBrokerChannel().taskExecutor().maxPoolSize(1)
        val channelInterceptor: ChannelInterceptor = object: ChannelInterceptor {
            override fun preSend(message: Message<*>, channel: MessageChannel): Message<*> {
                LOGGER.debug("Message broker sending message on Thread " + Thread.currentThread().id);
                return message
            }

            override fun postSend(message: Message<*>, channel: MessageChannel, sent: Boolean) {
                LOGGER.debug("Message broker sent message on Thread " + Thread.currentThread().id);
            }
        }
        config.configureBrokerChannel().interceptors(channelInterceptor)
    }

    override fun registerStompEndpoints(registry: StompEndpointRegistry) {
        registry.addEndpoint("/ws")
                .withSockJS()
    }

    override fun configureClientOutboundChannel(registration: ChannelRegistration) {
        registration.taskExecutor().corePoolSize(1)
        registration.taskExecutor().maxPoolSize(1)
    }

    override fun configureClientInboundChannel(registration: ChannelRegistration) {
        registration.taskExecutor().corePoolSize(1)
        registration.taskExecutor().maxPoolSize(1)
    }
}

(Stripped) code for sending the message:

@Controller
class StateController

@Autowired constructor(
    private val template: SimpMessagingTemplate
) {

....

    fun publishMsg(topicId: String, msg: MyMessageType){
        template.convertAndSend("/topic/msg/"+topicId, msg)
    }
}

Here is some examplary logging. As you can see, the executor is using more than one Thread, or rather, there seems to be more than one executor. Also, the Thread IDs are jumping back and forth, which to me looks like a clear confirmation that the dispatch execution is not as single-threaded as I would expect. Logging:

09:48:12.257 DEBUG [ault-executor-4] channelInterceptor$1.preSend             :  32  Message broker sending message on Thread 60
09:48:12.257 DEBUG [ault-executor-0] channelInterceptor$1.preSend             :  32  Message broker sending message on Thread 47
09:48:12.257 DEBUG [ault-executor-0] channelInterceptor$1.postSend            :  38  Message broker sent message on Thread 47
09:48:12.257 DEBUG [ault-executor-4] channelInterceptor$1.postSend            :  38  Message broker sent message on Thread 60

score 0 · Accepted Answer · answered Jan 08 '19 at 12:04

After further debugging I found my mistake. The different threads are from the submitting code. I should have added the channel interceptor to the outbound client channel, not the broker:

override fun configureClientOutboundChannel(registration: ChannelRegistration) {
    val channelInterceptor: ChannelInterceptor = object: ChannelInterceptor {
        override fun preSend(message: Message<*>, channel: MessageChannel): Message<*> {
            LOGGER.debug("Message broker sending message on Thread " + Thread.currentThread().id);
            return message
        }

        override fun postSend(message: Message<*>, channel: MessageChannel, sent: Boolean) {
            LOGGER.debug("Message broker sent message on Thread " + Thread.currentThread().id);
        }
    }
    registration.interceptors(channelInterceptor)
}

How to send Messages in spring boot via websocket broker in the order they were submitted?

1 Answers1